Reviews bash and POSIX sh scripts before they run in CI, cron or production. Flags missing strict mode, rm -rf on variables that may be empty, curl piped to a shell, eval, unquoted expansions, unchecked cd, parsing ls, chmod 777, hardcoded secrets, predictable /tmp files, ssh eating a read loop, masked exit codes and bashisms under /bin/sh, then returns a fixed script. Includes a stdlib Python linter with --self-test.
--- name: shell-script-safety-reviewer description: Reviews bash and POSIX sh scripts before they run in CI, cron or production. Flags missing strict mode, rm -rf on variables that may be empty, curl piped to a shell, eval, unquoted expansions, unchecked cd, parsing ls, chmod 777, hardcoded secrets, predictable /tmp files, ssh eating a read loop, masked exit codes and bashisms under /bin/sh, then returns a fixed script. Includes a stdlib Python linter with --self-test. --- # Shell Script Safety Reviewer You review shell scripts the way a careful SRE would before letting them run unattended: deploy scripts, cron jobs, CI steps, installers and Docker entrypoints. You find the lines that can delete the wrong data, leak a secret, run untrusted code or fail silently, explain each one in plain words, and hand back a corrected script that still does the same job. ## Files in this skill - `scripts/shell_lint.py` - line-based linter for bash and POSIX sh that understands quotes, comments, heredocs, [[ ]], (( )), assignments and case words; prints a findings table with fixes, or JSON (Python 3 standard library only) - `references/shell-pitfalls.md` - every rule the linter checks: what goes wrong, a minimal failing example and the fix - `references/safe-patterns.md` - a strict-mode header, safe temp files and cleanup, safe loops over files, argument parsing, secrets, downloads and logging - `templates/shell-review.md` - the review to hand back - `examples/deploy.sh` - a realistic deploy script with 20 findings (3 HIGH) - `examples/deploy-fixed.sh` - the same script after review; lints clean and passes ShellCheck ## Workflow ### 1. Get context Ask what runs the script (CI, cron, systemd, a human), which shell and OS (bash 5 on Ubuntu, sh on Alpine/busybox, macOS bash 3.2), who can control its inputs (arguments, environment, file names, network data) and whether it runs as root. Ask for the whole script, not a fragment: strict mode and traps live at the top. ### 2. Run the linter ``` python3 scripts/shell_lint.py examples/deploy.sh python3 scripts/shell_lint.py deploy.sh entrypoint.sh --min-severity MEDIUM python3 scripts/shell_lint.py install.sh --json --ignore BACKTICKS python3 scripts/shell_lint.py --self-test ``` Exit 1 means at least one HIGH finding, 2 means a file could not be read. Silence a deliberate line with `# shell-lint: disable=CODE`. If ShellCheck is available, run it too (`shellcheck -f gcc script.sh`) and merge the results; the linter adds checks ShellCheck does not do (secrets, curl | sh, chmod 777, fixed /tmp names, disabled TLS). ### 3. Review by hand The linter is a first pass. Read the script top to bottom and check what a regex cannot (see `references/shell-pitfalls.md`): - Which inputs are untrusted, and do they reach rm, eval, ssh, sql or a path? - Does every destructive step run only after its preconditions (right directory, non-empty variable, confirmed target host)? - Is it idempotent: can it run twice, or resume after failing halfway? - Are errors visible: does a failure in a pipe, subshell or function stop the script and leave a clear message? - Does it clean up temp files, locks and background jobs on exit and on Ctrl+C? ### 4. Fix and deliver Fill `templates/shell-review.md`: summary verdict, findings table (severity, line, problem, fix), the full fixed script, a diff of the important changes, and how to test it safely (dry run, `bash -n`, a throwaway directory or container, `set -x`). Keep the script's behavior; call out every behavior change. ## Example result `examples/deploy.sh`: 20 findings, 3 HIGH. A Slack token is hardcoded (HARDCODED_SECRET, rotate it), an installer is piped from curl into sudo bash (CURL_PIPE_SHELL), and `rm -rf $WEB_ROOT/*` wipes `/*` if WEB_ROOT is ever empty (RM_EMPTY_VAR). There is no `set -e`, so a failed `cd $BUILD_DIR` would run the rm and cp in the wrong directory; `ssh` inside the `while read host` loop eats hosts.txt, so only the first host restarts (SSH_STDIN_LOOP); `local count=$(...)` hides failures. `examples/deploy-fixed.sh` fixes all of them and lints clean. ## Rules - Rank by impact: data loss, code execution and secrets first, then silent failures, then style. - Quote by default; explain the one place where splitting is intended and use an array there. - Never suggest `set -e` as the only fix: also check pipes (pipefail), subshells, `local x=$(...)` and `if cmd` contexts where errexit is off. - Rotate any secret found in a script, even if the repo is private, and say so. - Prefer the POSIX form when the shebang is /bin/sh; otherwise make the shebang say bash. - Do not run a reviewed script against real systems to "test" it; use bash -n, a container or a dry-run flag. FILE:references/shell-pitfalls.md # Shell pitfalls checked by shell_lint.py Severity: HIGH = can delete data, run untrusted code or leak a secret. MEDIUM = wrong result or silent failure under realistic input. LOW = fragile or legacy style. ## HIGH ### RM_EMPTY_VAR / RM_ROOT `rm -rf $DIR/*` becomes `rm -rf /*` when DIR is empty or unset (typo, missing argument, failed command substitution). Steam's Linux client shipped exactly this bug in 2015. ```bash rm -rf -- "?DIR is empty"/* # aborts with a message if DIR is empty ``` `set -u` alone does not help when the variable is set to an empty string. ### CURL_PIPE_SHELL `curl https://x/install.sh | bash` runs whatever the server (or anyone in the middle) sends, and a dropped connection can run half a script. Download to a file, check a pinned SHA-256 or a signature, read it, then run it. ### EVAL_VAR `eval "$cmd"` executes any `;`, `$(...)` or backticks inside the data. Build commands as arrays: `cmd=(rsync -a -- "$src" "$dst"); "cmd[@]"`. For dispatch, use `case`. ### HARDCODED_SECRET A literal token, password or key in a script ends up in git history, CI logs (`set -x`) and `ps` output. Read it from the environment or a secret manager and fail early: `TOKEN="?"`. Rotate the exposed value; deleting the line does not remove it from history. ## MEDIUM ### NO_STRICT_MODE / NO_PIPEFAIL Without `set -e` a failed command is ignored and the next one runs anyway. Without `pipefail`, `build | tee log` succeeds when build fails. Use `set -euo pipefail` in bash and `set -eu` in POSIX sh. Know the gaps: errexit is ignored inside `if`, `while`, `&&`/`||` lists and functions called from them, and `local x=$(cmd)` (see below). ### UNQUOTED_VAR Unquoted `$var` and `$(cmd)` are split on IFS (spaces, tabs, newlines) and each piece is glob-expanded. `cp $src $dst` with `src="My File.txt"` copies two wrong files; `rm $f` with `f='*'` removes everything. Quote every expansion; use `"$@"` for all arguments and `"arr[@]"` for arrays. Safe without quotes: right side of `x=$y`, inside `[[ ]]` (except the right side of `==`/`=~` where it becomes a pattern), inside `(( ))`, and `case $x in`. ### CD_UNCHECKED If `cd build` fails, the rest runs in the current directory: `cd build; rm -rf *`. Use `cd -- "$dir" || exit 1` or strict mode. In loops, use a subshell: `(cd -- "$d" && make)`. ### LS_PARSING `for f in $(ls *.log)` breaks on spaces and newlines and runs the glob twice. Use the glob directly: `for f in ./*.log; do [ -e "$f" ] || continue; ...; done`, or `find . -name '*.log' -print0 | while IFS= read -r -d '' f; do ...; done`. ### CHMOD_777 World-writable files and directories let any local user or compromised service replace code or data. Use 755/644, 700/600 for private data, or `u=rwX,g=rX,o=`. ### PREDICTABLE_TMP / NO_TRAP_CLEANUP (LOW) A fixed `/tmp/app.log` can be pre-created as a symlink by another user (you then overwrite their target as root) and collides between parallel runs. Use `mktemp`/`mktemp -d` and remove it with `trap '...' EXIT`. ### LOCAL_MASKS_STATUS `local out=$(cmd)` returns the status of `local` (0), so `set -e` and `$?` never see cmd fail. The same goes for `export` and `readonly`. Declare first, assign on the next line. ### SSH_STDIN_LOOP `while read host; do ssh "$host" cmd; done < hosts.txt` stops after the first host because ssh reads the rest of stdin. Use `ssh -n` or `< /dev/null`. The same applies to ffmpeg, docker exec -i and anything else that reads stdin. ### TLS_DISABLED `curl -k`, `wget --no-check-certificate` and `StrictHostKeyChecking=no` turn off the check that you are talking to the right server. Fix the CA bundle, pin the host key in known_hosts, or use `StrictHostKeyChecking=accept-new` only for first contact on trusted networks. ### BASHISM_IN_SH Under `#!/bin/sh` (dash on Debian/Ubuntu, busybox on Alpine) these fail: `[[ ]]`, `==` in `[ ]`, `function f`, arrays, `source`, `<<<`, `&>`, `$'...'`. Switch the shebang to bash or use `[ ]`, `=`, `.`, and positional parameters. ## LOW - NO_SHEBANG: the caller's shell runs it; behavior differs between bash, zsh and sh. - READ_WITHOUT_R: `read` without `-r` eats backslashes; without `IFS=` it trims leading and trailing spaces. - BACKTICKS: hard to nest and quote; use `$(...)`. ## Not covered by the linter (check by hand) - Untrusted input reaching sql, ssh or paths (injection, `../` traversal); a leading `-` in file names (use `--`). - Race conditions on lock files; use `flock`. - Missing `wait` for background jobs, and orphaned jobs on exit. - Locale and tool differences (GNU vs BSD sed -i, date -d, readlink -f on macOS). - Logging secrets with `set -x`; turn xtrace off around secret handling. FILE:references/safe-patterns.md # Safe patterns for bash and sh scripts ## Header ```bash #!/usr/bin/env bash # What it does, how to call it, what it needs (env vars, tools). set -euo pipefail IFS=$'\n\t' # optional: no splitting on spaces readonly SCRIPT_DIR="$(cd -- "$(dirname -- "BASH_SOURCE[0]")" && pwd)" ``` POSIX sh: `set -eu` (pipefail exists in dash 0.5.11+ and busybox, but not everywhere). ## Fail with a message ```bash die() { printf 'error: %s\n' "$*" >&2; exit 1; } command -v jq >/dev/null 2>&1 || die "jq is required" [ -d "$TARGET" ] || die "no such directory: $TARGET" ``` ## Arguments ```bash usage() { echo "usage: $0 [-n] <release>" >&2; exit 2; } dry_run=0 while getopts ":n" opt; do case $opt in n) dry_run=1 ;; *) usage ;; esac done shift $((OPTIND - 1)) release="-"; [ -n "$release" ] || usage ``` ## Temp files and cleanup ```bash tmpdir="$(mktemp -d)" cleanup() { rm -rf -- "$tmpdir"; } trap cleanup EXIT trap 'exit 130' INT TERM # EXIT trap still runs ``` ## Destructive steps ```bash target="?WEB_ROOT is empty" case $target in /|/usr|/etc|"$HOME") die "refusing to clean $target" ;; esac run() { if [ "$dry_run" -eq 1 ]; then echo "+ $*"; else "$@"; fi; } run rm -rf -- "$target"/* ``` ## Loops over files and lines ```bash for f in "$dir"/*.csv; do [ -e "$f" ] || continue; process "$f"; done find "$dir" -type f -name '*.log' -print0 | while IFS= read -r -d '' f; do gzip -- "$f"; done while IFS= read -r line || [ -n "$line" ]; do echo "$line"; done < input.txt # last line without newline ``` ## Commands as data ```bash args=(--archive --delete -- "$src/" "$dst/") [ "$dry_run" -eq 1 ] && args=(--dry-run "args[@]") rsync "args[@]" ``` ## Secrets - Read from the environment or a file with 600 permissions: `token="$(<"$CRED_FILE")"`. - Pass to tools via stdin or env, not command-line arguments (visible in `ps`): `curl -H @- <<<"Authorization: Bearer $token"`. - `set +x` around secret handling. ## Downloads ```bash curl -fsSL --retry 3 -o "$tmpdir/tool.tgz" "$URL" echo "$SHA256 $tmpdir/tool.tgz" | sha256sum -c - ``` `-f` makes HTTP errors fail instead of saving the error page. ## Locking and idempotency ```bash exec 9>/var/lock/deploy.lock flock -n 9 || die "another deploy is running" mkdir -p -- "$dir" # no error if it exists ln -sfn -- "$release_dir" current # atomic switch of a symlink ``` ## Logging ```bash log() { printf '%s %s\n' "$(date -u +%FT%TZ)" "$*" >&2; } ``` Send logs to stderr so stdout stays clean for data. ## Testing a script safely 1. `bash -n script.sh` (syntax only), `shellcheck script.sh`, `python3 scripts/shell_lint.py script.sh`. 2. Run with a dry-run flag, then in a throwaway container: `docker run --rm -v "$PWD":/w -w /w bash:5 bash script.sh`. 3. Trace once with `bash -x script.sh` (secrets off). FILE:templates/shell-review.md # Shell script review: <script name> **Runs from:** <cron on web-01 as root / GitHub Actions ubuntu-24.04 / Docker entrypoint (Alpine, busybox sh)> **Shell:** <bash 5.2 / sh (dash)> **Untrusted inputs:** <$1 release tag, hosts.txt, file names in uploads/> **Verdict:** <BLOCK: 3 HIGH findings / OK with fixes / OK> **Summary:** <one or two sentences: the worst risk and what the fix changes> ## Findings | # | Severity | Code | Line | Problem | Fix | |---|---|---|---|---|---| | 1 | <HIGH> | <RM_EMPTY_VAR> | <15> | <rm -rf $WEB_ROOT/* deletes /* if WEB_ROOT is empty> | <rm -rf -- "?"/*> | ## Manual review notes - <inputs that reach rm/ssh/sql/paths, and how they are validated> - <idempotency: what happens if it runs twice or stops halfway> - <cleanup on exit and on Ctrl+C> ## Fixed script ```bash <full corrected script> ``` ## Key changes ```diff - rm -rf $WEB_ROOT/* + rm -rf -- "?"/* ``` ## Behavior changes - <now exits on the first failed command; previously continued> ## How to test safely 1. `bash -n <script>` and `python3 scripts/shell_lint.py <script>` (expect 0 HIGH) 2. `shellcheck <script>` if available 3. Dry run or a throwaway container: `<command>` 4. <rotate the exposed secret: where and who> FILE:examples/deploy.sh #!/bin/bash # Deploy the web app build to /srv/www and restart the service. # Usage: deploy.sh <release-tag> RELEASE=$1 BUILD_DIR=/srv/builds/$RELEASE WEB_ROOT=/srv/www SLACK_TOKEN="xoxb-0000-EXAMPLE-not-real" curl -fsSL https://get.example-tools.dev/install.sh | sudo bash cd $BUILD_DIR echo "Deploying $RELEASE" > /tmp/deploy.log rm -rf $WEB_ROOT/* cp -r dist/* $WEB_ROOT/ for f in $(ls $BUILD_DIR/migrations); do psql -f $BUILD_DIR/migrations/$f app_db done chmod -R 777 $WEB_ROOT/uploads while read host; do ssh -o StrictHostKeyChecking=no deploy@$host "sudo systemctl restart web" done < hosts.txt cleanup() { local count=$(ls /srv/builds | wc -l) echo "Builds on disk: $count" } cleanup curl -s -X POST -H "Authorization: Bearer $SLACK_TOKEN" \ -d "text=Deployed `date`" https://slack.com/api/chat.postMessage FILE:examples/deploy-fixed.sh #!/usr/bin/env bash # Deploy the web app build to /srv/www and restart the service. # Usage: SLACK_TOKEN=... deploy.sh <release-tag> set -euo pipefail RELEASE="?usage: deploy.sh <release-tag>" BUILD_DIR="/srv/builds/RELEASE" WEB_ROOT="/srv/www" SLACK_TOKEN="?set SLACK_TOKEN in the environment" # Installer is pinned and checked instead of curl | bash. installer="$(mktemp)" log="$(mktemp)" trap 'rm -f -- "$installer" "$log"' EXIT curl -fsSL -o "$installer" https://get.example-tools.dev/install-1.4.2.sh echo "3b1f0c9e2d4a5b6c7d8e9f00112233445566778899aabbccddeeff0011223344 $installer" | sha256sum -c - sudo bash "$installer" cd -- "$BUILD_DIR" echo "Deploying RELEASE" > "$log" rm -rf -- "?"/* cp -r dist/. "$WEB_ROOT/" for f in "$BUILD_DIR"/migrations/*.sql; do [ -e "$f" ] || continue psql -v ON_ERROR_STOP=1 -f "$f" app_db done chmod -R u=rwX,g=rX,o= "$WEB_ROOT/uploads" while IFS= read -r host; do ssh -n -o StrictHostKeyChecking=yes "deploy@host" "sudo systemctl restart web" done < hosts.txt report_builds() { local count count="$(find /srv/builds -mindepth 1 -maxdepth 1 -type d | wc -l)" echo "Builds on disk: count" } report_builds curl -fsS -X POST -H "Authorization: Bearer SLACK_TOKEN" \ --data-urlencode "text=Deployed RELEASE at $(date -u +%FT%TZ)" https://slack.com/api/chat.postMessage FILE:scripts/shell_lint.py #!/usr/bin/env python3 """Shell script safety linter (Python 3 standard library only). Reads a bash or POSIX sh script and flags the mistakes that cause data loss, security holes or silent failures: no strict mode, rm -rf on a variable that may be empty, curl | sh, eval on variables, unquoted expansions (word splitting and globbing), unchecked cd, parsing ls, chmod 777, hardcoded secrets, predictable /tmp files, mktemp without a cleanup trap, read without -r, ssh eating a while-read loop's input, local/export masking a failed command substitution, TLS or host-key checks turned off, backticks and bashisms in /bin/sh. It is a fast first pass, not a full parser: heredoc bodies are skipped, quotes, comments, [[ ]], (( )), assignments and case words are understood, and every finding names the line and a concrete fix. Silence a finding on one line with a trailing comment "# shell-lint: disable=CODE[,CODE]". Usage: python3 shell_lint.py script.sh [more.sh ...] [--json] [--min-severity MEDIUM] [--ignore CODE,CODE] python3 shell_lint.py --self-test Exit codes: 0 = no HIGH findings, 1 = at least one HIGH finding, 2 = unreadable input. """ import argparse, json, re, sys SEV_ORDER = {"HIGH": 0, "MEDIUM": 1, "LOW": 2, "INFO": 3} SECRET_NAME = re.compile(r"[A-Z0-9_]*(PASSWORD|PASSWD|TOKEN|SECRET|API_?KEY|ACCESS_KEY|PRIVATE_KEY)[A-Z0-9_]*") FIXES = { "NO_SHEBANG": "Add '#!/usr/bin/env bash' (or '#!/bin/sh' for POSIX) as line 1 so the right shell runs it.", "NO_STRICT_MODE": "Add 'set -euo pipefail' after the shebang (POSIX sh: 'set -eu') so failures stop the script.", "NO_PIPEFAIL": "Add 'set -o pipefail' so 'cmd | tee log' fails when cmd fails.", "RM_EMPTY_VAR": "Guard the variable: rm -rf -- \"?VAR is empty/\"... and quote it; never build rm paths from unchecked input.", "RM_ROOT": "Never rm the filesystem root or /*; point at a specific directory.", "CURL_PIPE_SHELL": "Download to a file, verify a checksum or signature, read it, then run it.", "EVAL_VAR": "Avoid eval; use arrays for commands (cmd=(ls -l \"$dir\"); \"cmd[@]\") or a case statement.", "UNQUOTED_VAR": "Quote expansions: \"$var\", \"arr[@]\", \"$(cmd)\" to stop word splitting and globbing.", "CD_UNCHECKED": "Use 'cd \"$dir\" || exit 1' (or enable set -e) so later commands do not run in the wrong directory.", "LS_PARSING": "Use a glob (for f in ./*.log) or find -print0 | while IFS= read -r -d '' f instead of parsing ls/find output.", "BACKTICKS": "Use $(...) instead of backticks; it nests and quotes predictably.", "CHMOD_777": "Grant only what is needed (755 for dirs/executables, 644 for files, 600 for secrets).", "HARDCODED_SECRET": "Read the secret from the environment or a secret manager (\"?\"), rotate the exposed value.", "PREDICTABLE_TMP": "Use tmp=$(mktemp) or tmpdir=$(mktemp -d) instead of a fixed /tmp name (symlink and race attacks).", "NO_TRAP_CLEANUP": "Add trap 'rm -rf -- \"$tmpdir\"' EXIT right after mktemp.", "READ_WITHOUT_R": "Use 'read -r' (and IFS= read -r line) so backslashes and leading spaces survive.", "LOCAL_MASKS_STATUS": "Split it: 'local out; out=$(cmd)' so set -e and $? see the command's failure.", "TLS_DISABLED": "Remove -k/--insecure/--no-check-certificate/StrictHostKeyChecking=no; fix the CA bundle or pin the host key.", "SSH_STDIN_LOOP": "Use 'ssh -n' (or ssh ... < /dev/null) inside while-read loops; otherwise ssh eats the rest of the input.", "BASHISM_IN_SH": "Either change the shebang to bash or use the POSIX form ([ ], =, . file, no arrays).", } class Finding: def __init__(self, sev, code, line, snippet, problem): self.sev, self.code, self.line, self.snippet, self.problem = sev, code, line, snippet, problem def as_dict(self): return {"severity": self.sev, "code": self.code, "line": self.line, "snippet": self.snippet, "problem": self.problem, "fix": FIXES.get(self.code, "")} def strip_comment(line): """Remove an unquoted comment. '#' starts a comment only at the start of a word.""" state, i = None, 0 while i < len(line): c = line[i] if state is None: if c == "\\": i += 2; continue if c in "'\"`": state = c elif c == "#" and (i == 0 or line[i - 1] in " \t;|&("): return line[:i].rstrip() elif state == "'": if c == "'": state = None else: if c == "\\": i += 2; continue if c == state: state = None i += 1 return line def logical_lines(text): """Yield (line_no, code_without_comment, raw_line, disabled_codes); heredoc bodies skipped.""" lines = text.split("\n") pending = [] # heredoc terminators waiting, in order out = [] for no, raw in enumerate(lines, 1): if pending: delim, dash = pending[0] body = raw.lstrip("\t") if dash else raw if body == delim: pending.pop(0) continue m = re.search(r"#\s*shell-lint:\s*disable=([A-Z_,\s]+)", raw) disabled = {c.strip() for c in m.group(1).split(",")} if m else set() code = strip_comment(raw) for hm in re.finditer(r"<<(-?)\s*(['\"]?)([A-Za-z_][A-Za-z0-9_]*)\2", code): if code[hm.start():hm.start() + 3] == "<<<": continue pending.append((hm.group(3), hm.group(1) == "-")) out.append((no, code, raw, disabled)) return out def match_paren(s, i): """s[i] == '(' ; return index of the matching ')' respecting quotes, or len(s).""" depth, state, j = 0, None, i while j < len(s): c = s[j] if state is None: if c == "\\": j += 2; continue if c in "'\"": state = c elif c == "(": depth += 1 elif c == ")": depth -= 1 if depth == 0: return j elif c == state: state = None elif c == "\\" and state == '"': j += 1 j += 1 return len(s) def unquoted_expansions(code): """Return names of $var / ... / $(...) / $@ expansions that are not inside quotes and not in a context where splitting cannot happen ([[ ]], (( )), assignments, case word).""" found = [] stripped = code.strip() if re.match(r"case\s", stripped): return found state, i, dbl_brackets, arith = None, 0, 0, 0 n = len(code) def word_start(k): while k > 0 and code[k - 1] not in " \t;|&(": k -= 1 return k while i < n: c = code[i] if state == "'": if c == "'": state = None i += 1; continue if c == "\\": i += 2; continue if state is None and c == "'": state = "'"; i += 1; continue if c == '"': state = None if state == '"' else '"' i += 1; continue if state is None and code.startswith("[[", i) and (i == 0 or code[i - 1] in " \t;&|!("): dbl_brackets += 1; i += 2; continue if state is None and code.startswith("]]", i) and dbl_brackets: dbl_brackets -= 1; i += 2; continue if state is None and code.startswith("((", i) and (i == 0 or code[i - 1] in " \t;&|!"): end = match_paren(code, i) i = end + 1; continue if c == "`": end = code.find("`", i + 1) i = (end if end != -1 else n) + 1; continue if c == "$" and i + 1 < n: nxt = code[i + 1] if code.startswith("$((", i): end = match_paren(code, i + 1) i = end + 1; continue if nxt == "(": end = match_paren(code, i + 1) inner = code[i + 2:end] found.extend(unquoted_expansions(inner)) if state is None and not dbl_brackets and not arith: ws = word_start(i) if not re.match(r"[A-Za-z_][A-Za-z0-9_]*(\[[^\]]*\])?\+?=", code[ws:i + 1]): found.append("$(" + inner.strip()[:20] + ")") i = end + 1; continue m = re.match(r"\$(\{[^}]*\}|[A-Za-z_][A-Za-z0-9_]*|[@*]|[0-9])", code[i:]) if m: tok = m.group(0) if state is None and not dbl_brackets: ws = word_start(i) is_assign = re.match(r"[A-Za-z_][A-Za-z0-9_]*(\[[^\]]*\])?\+?=", code[ws:i + 1]) if not is_assign and not tok.startswith("found.append(tok) i += len(tok); continue i += 1 return found def commands(code): """Split a line into simple commands on ; && || | (outside quotes).""" parts, cur, state, i = [], "", None, 0 while i < len(code): c = code[i] if state is None and c in "'\"": state = c elif state and c == state: state = None if state is None and c in ";|&": parts.append(cur); cur = "" while i + 1 < len(code) and code[i + 1] in ";|&": i += 1 i += 1; continue cur += c; i += 1 parts.append(cur) return [p.strip() for p in parts if p.strip()] def lint(text, name="script"): findings = [] lines = logical_lines(text) first = text.split("\n", 1)[0] shebang = first if first.startswith("#!") else "" is_posix_sh = bool(re.search(r"(^#!\s*/bin/sh\b|/env\s+sh\b|/bin/dash\b)", shebang)) all_code = "\n".join(c for _, c, _, _ in lines) strict_e = bool(re.search(r"(^|\n)\s*set\s+(-[a-zA-Z]*e[a-zA-Z]*\b|-o\s+errexit)", all_code)) or bool(re.search(r"\s-[a-z]*e", shebang)) pipefail = "pipefail" in all_code uses_pipes = "|" in all_code.replace("||", "") uses_mktemp = "mktemp" in all_code has_trap = bool(re.search(r"(^|\n)\s*trap\s", all_code)) def add(sev, code, no, snippet, problem, disabled=frozenset()): if code not in disabled: findings.append(Finding(sev, code, no, snippet.strip()[:80], problem)) if not shebang: add("LOW", "NO_SHEBANG", 1, first, "no shebang line; the caller's shell decides how this runs") if not strict_e: add("MEDIUM", "NO_STRICT_MODE", 1, shebang or first, "no 'set -e' (errexit): a failed command does not stop the script") elif uses_pipes and not pipefail and not is_posix_sh: add("LOW", "NO_PIPEFAIL", 1, shebang, "pipes are used but pipefail is off: only the last command's status counts") if uses_mktemp and not has_trap: no = next((n for n, c, _, _ in lines if "mktemp" in c), 1) add("LOW", "NO_TRAP_CLEANUP", no, next(c for n, c, _, _ in lines if n == no), "mktemp is used but nothing removes the temp file on exit or error") read_loop = 0 for no, code, raw, dis in lines: if not code.strip(): continue if re.search(r"(^|[;&|\s])while\b.*\bread\b", code): read_loop += 1 if read_loop and re.search(r"(^|[;&|\s])ssh\s", code) and not re.search(r"\bssh\s+(-\w+\s+)*-\w*n\b|<\s*/dev/null", code): add("MEDIUM", "SSH_STDIN_LOOP", no, code, "ssh inside a while-read loop reads the loop's stdin, so the loop stops after the first item", dis) if read_loop and re.search(r"(^|[;&|\s])done\b", code): read_loop -= 1 # curl | sh if re.search(r"\b(curl|wget)\b[^|]*\|\s*(sudo\s+(-\S+\s+)*)?(ba|z|da|k)?sh\b", code): add("HIGH", "CURL_PIPE_SHELL", no, code, "remote script piped straight into a shell: no review, no integrity check, partial downloads run", dis) if re.search(r"\b(curl\b[^|;]*\s(-k|--insecure)\b|wget\b[^|;]*--no-check-certificate|StrictHostKeyChecking=no)", code): add("MEDIUM", "TLS_DISABLED", no, code, "certificate or host-key verification is turned off (man-in-the-middle risk)", dis) if re.search(r"(^|[;&|(\s])eval\s+.*\$", code): add("HIGH", "EVAL_VAR", no, code, "eval on a string built from variables runs any shell code an attacker or odd filename puts in it", dis) if re.search(r"\bchmod\s+(-[A-Za-z]+\s+)*0?777\b|\bchmod\s+(-[A-Za-z]+\s+)*[augo]*\+rwx\b", code) and re.search(r"777|a\+rwx|o\+rwx", code): add("MEDIUM", "CHMOD_777", no, code, "world-writable permissions let any local user change the files", dis) if "`" in code: add("LOW", "BACKTICKS", no, code, "legacy backtick command substitution", dis) m = re.match(r"\s*(export\s+|readonly\s+|local\s+|declare\s+(-\w+\s+)*)?(" + SECRET_NAME.pattern + r")=(['\"]?)([^$'\"\s][^'\"\s]{3,)", code) if m: val = m.group(6) masked = val[:2] + "*" * max(3, len(val) - 4) + val[-2:] add("HIGH", "HARDCODED_SECRET", no, code.replace(val, masked), f"{m.group(3)} has a literal value in the script (ends up in git, logs and ps output)", dis) if re.match(r"\s*(local|export|declare|readonly)\s+(-\w+\s+)*[A-Za-z_][A-Za-z0-9_]*=\"?\$\(", code): add("MEDIUM", "LOCAL_MASKS_STATUS", no, code, "the builtin's exit status (0) hides a failure of the command substitution, even under set -e", dis) if re.search(r"(^|[^\w.-])/tmp/[A-Za-z0-9_.${}-]+", code) and "mktemp" not in code: add("MEDIUM", "PREDICTABLE_TMP", no, code, "fixed /tmp path: another user can pre-create or symlink it, and parallel runs collide", dis) if re.search(r"\bfor\s+\w+\s+in\s+(\$\(|`)\s*(ls|find)\b", code) or re.search(r"\bls\b[^|]*\|\s*(while|xargs)\b", code): add("MEDIUM", "LS_PARSING", no, code, "parsing ls/find output breaks on spaces, newlines and glob characters in filenames", dis) for cmd in commands(code): words = cmd.split() if not words: continue w0 = words[0] while w0 in ("sudo", "command", "builtin", "exec", "!", "while", "until", "if", "then", "do", "else", "elif", "{", "(") and len(words) > 1: words = words[1:]; w0 = words[0] if w0 == "rm": args = words[1:] rec = any(re.match(r"-[a-zA-Z]*[rR]", a) or a == "--recursive" for a in args) if any(a.strip("'\"") in ("/", "/*") for a in args): add("HIGH", "RM_ROOT", no, cmd, "rm targets / or /*", dis) for a in args: if a.startswith("-") and a != "--": continue if "$" in a and not re.search(r"\$\{[A-Za-z_][A-Za-z0-9_]*:\?", a): a_clean = a.strip("'\"") if re.match(r"\$\{?[A-Za-z_][A-Za-z0-9_]*\}?(/|\"?$)", a_clean) or rec: add("HIGH" if rec else "MEDIUM", "RM_EMPTY_VAR", no, cmd, f"rm{' -r' if rec else ''} on {a}: if the variable is empty or unset this deletes the wrong path (e.g. '/')", dis) break if w0 == "cd" and not strict_e: if not re.search(re.escape(cmd) + r"\s*(\|\||&&)", code) and not re.search(r"(\|\||&&)\s*" + re.escape(cmd), code): add("MEDIUM", "CD_UNCHECKED", no, cmd, "cd may fail and the following commands then run in the wrong directory", dis) if w0 == "read": opts = [a for a in words[1:] if a.startswith("-")] if not any("r" in o for o in opts): add("LOW", "READ_WITHOUT_R", no, cmd, "read without -r mangles backslashes", dis) exps = unquoted_expansions(code) if exps: uniq = list(dict.fromkeys(exps)) shown = ", ".join(uniq[:4]) + (" ..." if len(uniq) > 4 else "") only_echo = re.match(r"\s*(echo|printf)\s+[^|>]*$", code) and not any(e in ("$@", "$*") for e in uniq) if only_echo: add("LOW", "UNQUOTED_VAR", no, code, "unquoted " + shown + " in echo/printf: spacing collapses and * expands", dis) else: add("MEDIUM", "UNQUOTED_VAR", no, code, "unquoted " + shown + ": word splitting and glob expansion", dis) if is_posix_sh: bash = [] if re.search(r"(^|[\s;&|!])\[\[\s", code): bash.append("[[ ]]") if re.search(r"(^|[\s;&|])\[\s[^]]*\s==\s", code): bash.append("== in [ ]") if re.match(r"\s*function\s+\w+", code): bash.append("function keyword") if re.search(r"\b[A-Za-z_]\w*=\(", code): bash.append("array") if re.match(r"\s*source\s", code): bash.append("source") if "<<<" in code: bash.append("here-string") if re.search(r"&>", code): bash.append("&>") if re.search(r"\$'", code): bash.append("$'...'") if bash: add("MEDIUM", "BASHISM_IN_SH", no, code, "bash-only syntax under #!/bin/sh (" + ", ".join(bash) + "); dash and busybox sh will fail", dis) findings.sort(key=lambda f: (SEV_ORDER[f.sev], f.line, f.code)) return findings def render_md(name, findings): counts = {s: sum(1 for f in findings if f.sev == s) for s in SEV_ORDER} out = [f"# Shell lint: {name}", "", f"Findings: {len(findings)} (HIGH {counts['HIGH']}, MEDIUM {counts['MEDIUM']}, LOW {counts['LOW']})", ""] if not findings: out.append("No findings.") return "\n".join(out) out += ["| Severity | Code | Line | Snippet | Problem |", "|---|---|---|---|---|"] for f in findings: snip = f.snippet.replace("|", "\\|").replace("`", "'") out.append(f"| {f.sev} | {f.code} | {f.line} | `{snip}` | {f.problem.replace('|', '/')} |") out += ["", "## Fixes", ""] for code in dict.fromkeys(f.code for f in findings): out.append(f"- {code}: {FIXES[code]}") return "\n".join(out) # ---------------------------------------------------------------- self-test def _codes(src): return [f.code for f in lint(src)] def self_test(): S = "#!/usr/bin/env bash\nset -euo pipefail\n" cases = [ ("clean script has no findings", S + 'dir="$1"\ncp -- "$dir/a" "$dir/b"\n', lambda c: c == []), ("missing shebang", 'set -eu\necho "hi"\n', lambda c: "NO_SHEBANG" in c), ("missing strict mode", "#!/bin/bash\necho ok\n", lambda c: "NO_STRICT_MODE" in c), ("set -e without pipefail and a pipe", "#!/bin/bash\nset -e\nmake | tee log\n", lambda c: "NO_PIPEFAIL" in c), ("set -o errexit counts as strict", "#!/bin/bash\nset -o errexit\nset -o pipefail\necho ok\n", lambda c: c == []), ("rm -rf $VAR/ is HIGH", S + 'rm -rf "$BUILD_DIR"/\n', lambda c: "RM_EMPTY_VAR" in c), ("rm -rf ? is fine", S + 'rm -rf -- "?/"\n', lambda c: "RM_EMPTY_VAR" not in c), ("rm -rf / is RM_ROOT", S + "rm -rf /\n", lambda c: "RM_ROOT" in c), ("curl | bash", S + "curl -fsSL https://x.example/install.sh | sudo bash\n", lambda c: "CURL_PIPE_SHELL" in c), ("curl to file is fine", S + 'curl -fsSLo install.sh "$URL"\n', lambda c: "CURL_PIPE_SHELL" not in c), ("eval with variable", S + 'eval "$cmd"\n', lambda c: "EVAL_VAR" in c), ("unquoted var in command", S + "cp $src $dst\n", lambda c: "UNQUOTED_VAR" in c), ("quoted var is fine", S + 'cp "$src" "$dst"\n', lambda c: "UNQUOTED_VAR" not in c), ("assignment rhs is fine", S + "x=$y\nn=$(date +%s)\n", lambda c: "UNQUOTED_VAR" not in c), ("[[ ]] is fine", S + "if [[ $a == b ]]; then :; fi\n", lambda c: "UNQUOTED_VAR" not in c), ("arith is fine", S + "n=$(( $a + 1 ))\n(( count > $max ))\n", lambda c: "UNQUOTED_VAR" not in c), ("#arr is fine", S + 'printf "%s\\n" #arr[@]\n', lambda c: "UNQUOTED_VAR" not in c), ("unquoted $@", S + "run $@\n", lambda c: "UNQUOTED_VAR" in c), ("unquoted cmd substitution", S + "rm -- $(cat list)\n", lambda c: "UNQUOTED_VAR" in c), ("var inside quoted $( ) still checked", S + 'x="$(basename $path)"\n', lambda c: "UNQUOTED_VAR" in c), ("single quotes protect", S + "echo '$HOME is literal'\n", lambda c: "UNQUOTED_VAR" not in c), ("comment ignored", S + "# rm -rf $DIR/ and curl x | sh\n", lambda c: c == []), ("heredoc body skipped", S + "cat <<'EOF'\nrm -rf $X/\ncurl a | sh\nEOF\n", lambda c: c == []), ("cd unchecked without set -e", "#!/bin/bash\ncd /srv/app\n", lambda c: "CD_UNCHECKED" in c), ("cd || exit is fine", "#!/bin/bash\ncd /srv/app || exit 1\n", lambda c: "CD_UNCHECKED" not in c), ("for in $(ls)", S + "for f in $(ls *.log); do :; done\n", lambda c: "LS_PARSING" in c), ("backticks", S + "d=`date`\n", lambda c: "BACKTICKS" in c), ("chmod 777", S + "chmod -R 777 /srv/app\n", lambda c: "CHMOD_777" in c), ("hardcoded token, value masked", S + 'export API_TOKEN="sk_live_abcdef123456"\n', lambda c: "HARDCODED_SECRET" in c), ("secret from env is fine", S + 'API_TOKEN="?"\n', lambda c: "HARDCODED_SECRET" not in c), ("predictable tmp", S + 'echo "x" > /tmp/deploy.lock\n', lambda c: "PREDICTABLE_TMP" in c), ("mktemp without trap", S + "tmp=$(mktemp)\n", lambda c: "NO_TRAP_CLEANUP" in c), ("mktemp with trap fine", S + "tmp=$(mktemp)\ntrap 'rm -f -- \"$tmp\"' EXIT\n", lambda c: "NO_TRAP_CLEANUP" not in c), ("read without -r", S + 'while read line; do :; done < "$f"\n', lambda c: "READ_WITHOUT_R" in c), ("local masks status", S + "f() {\n local out=$(git rev-parse HEAD)\n}\n", lambda c: "LOCAL_MASKS_STATUS" in c), ("curl -k", S + 'curl -k "$URL" -o x\n', lambda c: "TLS_DISABLED" in c), ("bashisms under /bin/sh", "#!/bin/sh\nset -eu\nif [[ -n \"$x\" ]]; then source ./env; fi\n", lambda c: "BASHISM_IN_SH" in c), ("bash allows [[ ]]", S + 'if [[ -n "$x" ]]; then source ./env; fi\n', lambda c: "BASHISM_IN_SH" not in c), ("disable comment", S + "cp $a $b # shell-lint: disable=UNQUOTED_VAR\n", lambda c: "UNQUOTED_VAR" not in c), ("ssh in while-read loop", S + 'while IFS= read -r h; do\n ssh "$h" uptime\ndone < hosts\n', lambda c: "SSH_STDIN_LOOP" in c), ("ssh -n in loop is fine", S + 'while IFS= read -r h; do\n ssh -n "$h" uptime\ndone < hosts\n', lambda c: "SSH_STDIN_LOOP" not in c), ("case word fine", S + 'case $1 in\n a) echo "a" ;;\nesac\n', lambda c: "UNQUOTED_VAR" not in c), ] passed = 0 for name, src, check in cases: got = _codes(src) ok = check(got) passed += ok print(("PASS " if ok else "FAIL ") + name + ("" if ok else f" -> {got}")) # masking check and exit code check f = [x for x in lint(S + 'export API_TOKEN="sk_live_abcdef123456"\n') if x.code == "HARDCODED_SECRET"][0] ok = "abcdef123456" not in f.snippet passed += ok; print(("PASS " if ok else "FAIL ") + "secret value masked in output") ok = render_md("t", []).endswith("No findings.") passed += ok; print(("PASS " if ok else "FAIL ") + "empty report") total = len(cases) + 2 print(f"{passed}/{total} passed") return 0 if passed == total else 1 def main(): ap = argparse.ArgumentParser(description="Shell script safety linter (stdlib only)") ap.add_argument("files", nargs="*") ap.add_argument("--json", action="store_true") ap.add_argument("--min-severity", default="LOW", choices=list(SEV_ORDER)) ap.add_argument("--ignore", default="", help="comma-separated codes to skip") ap.add_argument("--self-test", action="store_true") a = ap.parse_args() if a.self_test: return self_test() if not a.files: ap.error("give at least one script or --self-test") ignore = {c.strip() for c in a.ignore.split(",") if c.strip()} worst, reports, js = 0, [], {} for path in a.files: try: with open(path, encoding="utf-8") as fh: text = fh.read() except (OSError, UnicodeDecodeError) as e: print(f"error: cannot read {path}: {e}", file=sys.stderr) return 2 fs = [f for f in lint(text, path) if f.code not in ignore and SEV_ORDER[f.sev] <= SEV_ORDER[a.min_severity]] if any(f.sev == "HIGH" for f in fs): worst = 1 js[path] = [f.as_dict() for f in fs] reports.append(render_md(path, fs)) print(json.dumps(js, indent=2) if a.json else "\n\n".join(reports)) return worst if __name__ == "__main__": sys.exit(main())
Reviews HTTP caching headers (Cache-Control, Expires, ETag, Last-Modified, Vary, Set-Cookie) for pages, assets, APIs. Computes browser and CDN freshness, flags cookie or personal responses a CDN may share, HTML cached too long, hashed assets cached too briefly, immutable on changing URLs, Vary fragmentation, missing validators, heuristic caching and cached errors. Suggests a header per resource. Includes a stdlib Python checker with --self-test.
---
name: http-cache-header-reviewer
description: Reviews HTTP caching headers (Cache-Control, Expires, ETag, Last-Modified, Vary, Set-Cookie) for pages, assets, APIs. Computes browser and CDN freshness, flags cookie or personal responses a CDN may share, HTML cached too long, hashed assets cached too briefly, immutable on changing URLs, Vary fragmentation, missing validators, heuristic caching and cached errors. Suggests a header per resource. Includes a stdlib Python checker with --self-test.
---
# HTTP Cache Header Reviewer
You help web developers get caching right: fast repeat visits and low CDN bills without stale pages after a deploy or, worse, one user's data served to another. You collect real response headers, explain what each cache will actually do with them, and propose a header per resource type with a short fix list.
## Files in this skill
- `scripts/cache_audit.py` - reads response blocks (curl -sI or DevTools output) and prints resource kind, browser and CDN TTL, revalidation, flags and suggested Cache-Control (Python 3 standard library only)
- `references/cache-control-directives.md` - every directive, freshness and heuristic rules, validators, Vary, cacheable status codes
- `references/caching-strategy-playbook.md` - recommended headers per resource, deploy safety, CDN notes, how to collect and verify headers
- `templates/cache-review-report.md` - report with current vs recommended headers and a fix list
- `examples/shop-responses.txt` - eight responses from a sample shop with common mistakes
## Workflow
### 1. Collect headers
Ask for a list of representative URLs: the home page, a logged-in page, a hashed JS/CSS file, an unhashed script, an image, a font, a public API call, a personal API call, an error response. Capture with `curl -sI <url>` (add `-H 'Cookie: ...'` or `-H 'Authorization: ...'` for logged-in requests, never paste real tokens into the report) or DevTools. Put each in the block format of `examples/shop-responses.txt`: a `### METHOD URL` line, optional `> Request-Header: value` lines, the status line, then the response headers.
### 2. Run the checker
```
python3 scripts/cache_audit.py examples/shop-responses.txt
python3 scripts/cache_audit.py headers.txt --json > cache-report.json
python3 scripts/cache_audit.py --self-test
```
Exit code 1 means high-severity findings, 2 means the input could not be parsed.
### 3. Explain the findings
Order: privacy first (AUTH_SHARED_CACHE, PUBLIC_WITH_COOKIE, PERSONAL_NOT_PRIVATE), then correctness after deploys (HTML_LONG_TTL, IMMUTABLE_UNHASHED, ERROR_CACHED), then performance (HASHED_SHORT_TTL, ASSET_NO_CACHING, VARY_FRAGMENTS, NO_VALIDATOR, HEURISTIC_ONLY) and hygiene (INVALID_DIRECTIVE, NO_STORE_CONFLICT, EXPIRES_ONLY, PRAGMA_ONLY). Use `references/cache-control-directives.md` to explain why.
### 4. Recommend headers
Use `references/caching-strategy-playbook.md`. Give the exact header per resource and where to set it in the user's stack (Nginx `add_header`, Express `res.set`, Next.js `headers()`, S3/CloudFront metadata, Cloudflare rules). Mention the deploy rule: hashed assets for a year, HTML revalidates.
### 5. Verify and report
Fill `templates/cache-review-report.md`. After changes, collect headers again and re-run the checker; check CDN HIT/MISS headers.
## Example result
For `examples/shop-responses.txt`: 5 high findings (home page HTML cached 1 day, widget.js immutable without a hash, the cart API with a session cookie cached by the CDN for 2 minutes, the login page with Set-Cookie marked public and cached 10 minutes), 4 medium (app.3f9a1c7b.js cached only 1 hour, hero.jpg on an 8.1-day heuristic, Vary: Cookie, a 503 cached for 1 hour) and 1 low (cart API has no validator); only vendor.81d2e0aa.css is already ideal.
## Rules
- Treat any chance of a shared cache storing personal data as the top issue.
- Do not ask for or keep real cookies or tokens; placeholders are enough.
- Recommend purges or URL versioning when changing TTLs that are already live.
- Say when behavior depends on the CDN's configuration and suggest checking it.
FILE:references/cache-control-directives.md
# Cache-Control Directives and Freshness Rules
## Response directives
| Directive | Meaning |
|---|---|
| max-age=N | Fresh for N seconds in any cache (browser and shared) |
| s-maxage=N | Overrides max-age for shared caches (CDN, proxy) only |
| no-cache | May be stored, but must be revalidated with the origin before every use |
| no-store | Must not be stored anywhere; overrides everything else |
| private | Only the browser may store it; CDNs and proxies must not |
| public | Shared caches may store it even if it would normally not be cacheable (for example with Authorization) |
| must-revalidate | Once stale, must not be served without a successful revalidation |
| proxy-revalidate | Same as must-revalidate, for shared caches only |
| immutable | Will never change while fresh; browsers skip revalidation on reload |
| stale-while-revalidate=N | May serve stale for N seconds while refreshing in the background |
| stale-if-error=N | May serve stale for N seconds if the origin returns 5xx or is unreachable |
| no-transform | Intermediaries must not modify the body (recompress images, etc.) |
Common mistakes: `no-cache` does NOT mean "do not cache" (that is `no-store`); `max-age` values must be whole seconds (`max-age=10m` is invalid and ignored); `Pragma: no-cache` only works on requests.
## Freshness lifetime (RFC 9111)
1. Shared cache: s-maxage, else max-age, else Expires - Date.
2. Browser: max-age, else Expires - Date.
3. Neither present and Last-Modified present: caches may use a heuristic, usually 10% of (Date - Last-Modified). A file last changed 80 days ago may be reused for 8 days with no check.
4. `private` sets the shared lifetime to 0. `no-store` sets both to 0.
## Validators and revalidation
- ETag (strong `"abc"` or weak `W/"abc"`) -> client sends If-None-Match.
- Last-Modified -> client sends If-Modified-Since.
- A match returns `304 Not Modified` with no body, which is cheap. Without a validator, every revalidation downloads the whole body.
## Vary
- `Vary: Accept-Encoding` is normal and safe.
- `Vary: Cookie`, `User-Agent` or `Referer` creates one cache entry per distinct value, which usually means no CDN hits.
- `Vary: *` means the response can never be reused.
## Status codes
Cacheable by default when fresh: 200, 203, 204, 206, 300, 301, 308, 404, 405, 410, 414, 501. Error responses (4xx/5xx) should have short or no caching, or a CDN may serve an outage page for hours. Use `stale-if-error` to serve the last good copy instead.
FILE:references/caching-strategy-playbook.md
# Caching Strategy Playbook
## Recommended headers by resource
| Resource | Cache-Control | Notes |
|---|---|---|
| HTML pages, app shell | `no-cache` + ETag | Always fresh after deploys; 304s keep it cheap |
| Marketing HTML on a CDN | `public, max-age=0, s-maxage=300, stale-while-revalidate=60` | Purge the CDN on publish |
| JS/CSS with a content hash (`app.3f9a1c7b.js`) | `public, max-age=31536000, immutable` | New build = new URL |
| JS/CSS without a hash | `public, max-age=300, stale-while-revalidate=86400` | Or add hashing to the build |
| Images, user uploads with stable URLs | `public, max-age=86400, stale-while-revalidate=604800` | Version the URL when the image changes |
| Fonts (versioned URL) | `public, max-age=31536000, immutable` | Also send CORS headers |
| Public API data (prices, catalog) | `public, max-age=30, s-maxage=300, stale-if-error=600` | Keep TTLs short; purge on change |
| Personal API data (cart, profile) | `private, no-cache` + ETag | Never public |
| Secrets, banking, health records, one-time tokens | `no-store` | Also on the logout and account pages |
| Redirect 301 | `max-age=86400` at first | Browsers can cache a bare 301 forever |
| Errors 5xx | `no-store` or `max-age=0`, use stale-if-error on the good responses | |
## Deploy safety
1. Hash every built asset name, then cache it for a year.
2. Make HTML revalidate so it always points at the current hashes.
3. Keep old hashed assets online for at least one release so open tabs still work.
4. Never put `immutable` on a URL whose content can change.
## CDN notes
- Most CDNs ignore `private`/`no-store` only if misconfigured; check "respect origin headers".
- Many CDNs do not cache responses with Set-Cookie by default; some do if `public` is set. Strip Set-Cookie from static responses.
- Use a `Surrogate-Control` or CDN-Cache-Control header if the CDN supports it and you want a CDN TTL different from the browser TTL.
- Normalize the cache key (ignore tracking query strings like utm_*).
## How to collect headers
```
curl -sI https://example.com/ ; curl -sI -H 'Cookie: session=...' https://example.com/api/me
curl -s -o /dev/null -D - https://example.com/assets/app.js # GET instead of HEAD
```
Some servers answer HEAD differently from GET; when in doubt use the GET form. In Chrome DevTools: Network tab, select a request, Headers, Response Headers (copy as text).
## Checking the result
- Reload twice in DevTools: hashed assets should show "(memory cache)" or "(disk cache)", HTML should show 304 or 200.
- CDN: look at its `Age`, `X-Cache` or `CF-Cache-Status` header (HIT / MISS / BYPASS).
FILE:templates/cache-review-report.md
# HTTP Cache Review - <site / service> - <date>
**Scope:** <URLs or HAR file> **CDN:** <name or none> **Collected with:** <curl -sI / DevTools / HAR>
## Summary
- Responses reviewed: <n> High: <n> Medium: <n> Low: <n>
- Biggest risk: <for example personal API cached on the CDN>
- Biggest win: <for example year-long caching for hashed assets>
## Current vs recommended
| Resource | Kind | Current Cache-Control | Browser / CDN TTL | Flags | Recommended |
|---|---|---|---|---|---|
| | | | | | |
## Fix list
| Priority | Change | Where (server, framework, CDN rule) | Owner | Done |
|---|---|---|---|---|
| 1 | | | | [ ] |
## Verification
- [ ] Re-run `python3 scripts/cache_audit.py` on fresh headers: no high findings
- [ ] CDN shows HIT for static files, BYPASS/MISS for personal API
- [ ] Deploy test: new HTML loads new assets without a hard refresh
FILE:examples/shop-responses.txt
# Responses captured with: curl -sI <url> (request headers sent are listed with "> ")
### GET https://shop.example/
HTTP/2 200
content-type: text/html; charset=utf-8
cache-control: public, max-age=86400
date: Wed, 21 Oct 2026 07:00:00 GMT
### GET https://shop.example/assets/app.3f9a1c7b.js
HTTP/2 200
content-type: application/javascript
cache-control: public, max-age=3600
etag: "3f9a1c7b"
### GET https://shop.example/assets/vendor.81d2e0aa.css
HTTP/2 200
content-type: text/css
cache-control: public, max-age=31536000, immutable
etag: "81d2e0aa"
### GET https://shop.example/js/widget.js
HTTP/2 200
content-type: application/javascript
cache-control: public, max-age=31536000, immutable
### GET https://shop.example/img/hero.jpg
HTTP/2 200
content-type: image/jpeg
date: Wed, 21 Oct 2026 07:00:00 GMT
last-modified: Sat, 01 Aug 2026 07:00:00 GMT
### GET https://shop.example/api/cart
> Cookie: session=abc123
HTTP/2 200
content-type: application/json
cache-control: public, s-maxage=120
vary: Cookie
### POST https://shop.example/login
HTTP/2 200
content-type: text/html; charset=utf-8
cache-control: public, max-age=600
set-cookie: session=xyz789; HttpOnly; Secure; SameSite=Lax
### GET https://shop.example/api/products?page=1
HTTP/2 503
content-type: application/json
cache-control: public, max-age=3600
FILE:scripts/cache_audit.py
#!/usr/bin/env python3
"""HTTP caching header reviewer (Python 3 standard library only).
Input: a text file with one block per response, as copied from `curl -sI`, browser
devtools or a HAR export:
### GET https://shop.example/assets/app.3f9a1c7b.js
> Authorization: Bearer ... (optional request headers start with "> ")
HTTP/2 200
content-type: application/javascript
cache-control: public, max-age=31536000, immutable
etag: "3f9a1c7b"
Blank lines and lines starting with "#" (but not "###") are ignored.
For each response it works out the kind (html, hashed-asset, asset, api, image, font, other),
browser and shared-cache (CDN) freshness in seconds (s-maxage > max-age > Expires - Date >
10% heuristic from Last-Modified), whether it can be revalidated, and flags:
NO_STORE_CONFLICT, PUBLIC_WITH_COOKIE, AUTH_SHARED_CACHE, PERSONAL_NOT_PRIVATE, VARY_STAR,
VARY_FRAGMENTS, HTML_LONG_TTL, HASHED_SHORT_TTL, IMMUTABLE_UNHASHED, ASSET_NO_CACHING,
NO_VALIDATOR, HEURISTIC_ONLY, EXPIRES_ONLY, PRAGMA_ONLY, ERROR_CACHED, INVALID_DIRECTIVE.
It suggests a Cache-Control value per kind.
Usage:
python3 cache_audit.py responses.txt
python3 cache_audit.py responses.txt --json
python3 cache_audit.py --self-test
Exit code: 0 OK, 1 high-severity flags found, 2 bad input.
"""
import argparse
import email.utils
import json
import re
import sys
KNOWN = {"max-age", "s-maxage", "no-cache", "no-store", "no-transform", "must-revalidate",
"proxy-revalidate", "must-understand", "private", "public", "immutable",
"stale-while-revalidate", "stale-if-error"}
NEEDS_INT = {"max-age", "s-maxage", "stale-while-revalidate", "stale-if-error"}
HASH_RE = re.compile(r"[.\-_]([0-9a-f]{8,}|[0-9A-Za-z_-]{8,}(?=\.[a-z0-9]+$))\.[a-z0-9]+$")
SEVERITY = {"NO_STORE_CONFLICT": "low", "PUBLIC_WITH_COOKIE": "high", "AUTH_SHARED_CACHE": "high",
"PERSONAL_NOT_PRIVATE": "medium", "VARY_STAR": "medium", "VARY_FRAGMENTS": "medium",
"HTML_LONG_TTL": "high", "HASHED_SHORT_TTL": "medium", "IMMUTABLE_UNHASHED": "high",
"ASSET_NO_CACHING": "medium", "NO_VALIDATOR": "low", "HEURISTIC_ONLY": "medium",
"EXPIRES_ONLY": "low", "PRAGMA_ONLY": "low", "ERROR_CACHED": "medium",
"INVALID_DIRECTIVE": "medium"}
RECOMMEND = {
"html": "no-cache (plus ETag or Last-Modified), or max-age=0, must-revalidate",
"hashed-asset": "public, max-age=31536000, immutable",
"asset": "public, max-age=3600, stale-while-revalidate=86400 (or add a content hash to the file name)",
"image": "public, max-age=86400, stale-while-revalidate=604800",
"font": "public, max-age=31536000, immutable (if the URL is versioned)",
"api": "private, no-cache for user data; public, max-age=60, s-maxage=300 only for truly public data",
"personal": "private, no-cache (or no-store for sensitive data)",
"other": "set an explicit Cache-Control",
}
class CacheError(ValueError):
pass
def parse_cc(value):
"""Return (directives dict, problems list)."""
d, problems = {}, []
for part in [p.strip() for p in value.split(",") if p.strip()]:
k, eq, v = part.partition("=")
k = k.strip().lower()
v = v.strip().strip('"')
if k not in KNOWN:
problems.append(f"unknown directive {k!r}")
continue
if k in NEEDS_INT:
if not re.fullmatch(r"\d+", v or ""):
problems.append(f"{k} needs a whole number of seconds, got {v!r}")
continue
d[k] = int(v)
else:
d[k] = True if not eq else v
return d, problems
def parse_blocks(text):
blocks, cur = [], None
for raw in text.splitlines():
line = raw.rstrip("\r")
if line.startswith("###"):
cur = {"label": line[3:].strip(), "status": None, "headers": {}, "request": {}}
blocks.append(cur)
continue
if not line.strip() or line.lstrip().startswith("#"):
continue
if cur is None:
raise CacheError("file must start with a '### METHOD URL' line")
if line.startswith(">"):
k, _, v = line[1:].strip().partition(":")
cur["request"][k.strip().lower()] = v.strip()
continue
m = re.match(r"HTTP/[\d.]+\s+(\d{3})", line)
if m:
cur["status"] = int(m.group(1))
continue
k, colon, v = line.partition(":")
if not colon:
raise CacheError(f"cannot parse header line {line!r} in block {cur['label']!r}")
k = k.strip().lower()
if k in cur["headers"] and k in ("cache-control", "vary"):
cur["headers"][k] += ", " + v.strip()
elif k == "set-cookie":
cur["headers"].setdefault(k, []).append(v.strip())
else:
cur["headers"][k] = v.strip()
if not blocks:
raise CacheError("no response blocks found")
return blocks
def url_of(label):
parts = label.split()
return parts[-1] if parts else ""
def kind_of(url, ctype):
path = re.sub(r"[?#].*$", "", url)
name = path.rsplit("/", 1)[-1].lower()
ctype = ctype.lower()
hashed = bool(HASH_RE.search(name)) and bool(re.search(r"\d", name))
if "text/html" in ctype or name.endswith(".html") or (not ctype and "." not in name):
return "html", False
if "json" in ctype or "/api/" in path or "graphql" in path:
return "api", False
if name.endswith((".woff2", ".woff", ".ttf", ".otf")) or "font" in ctype:
return "font", hashed
if ctype.startswith("image/") or name.endswith((".png", ".jpg", ".jpeg", ".gif", ".webp", ".avif", ".svg", ".ico")):
return ("hashed-asset" if hashed else "image"), hashed
if name.endswith((".js", ".mjs", ".css", ".map", ".wasm")) or "javascript" in ctype or "text/css" in ctype:
return ("hashed-asset" if hashed else "asset"), hashed
return "other", hashed
def http_date(v):
try:
return email.utils.parsedate_to_datetime(v)
except (TypeError, ValueError, IndexError):
return None
def review(block):
h, req = block["headers"], block["request"]
status = block["status"] or 200
url = url_of(block["label"])
kind, hashed = kind_of(url, h.get("content-type", ""))
cc, problems = parse_cc(h.get("cache-control", ""))
flags = []
def flag(code, detail):
flags.append({"code": code, "severity": SEVERITY[code], "detail": detail})
for p in problems:
flag("INVALID_DIRECTIVE", p)
cookies = h.get("set-cookie", [])
auth = "authorization" in req or "cookie" in req
date, expires, lastmod = http_date(h.get("date")), h.get("expires"), http_date(h.get("last-modified"))
no_store = "no-store" in cc
heuristic = False
if no_store:
browser = shared = 0
else:
browser = cc.get("max-age")
if browser is None and expires is not None:
ex = http_date(expires)
browser = max(0, int((ex - date).total_seconds())) if ex and date else 0
if browser is None and "no-cache" not in cc and lastmod and date and status in (200, 203, 204, 206, 300, 301, 404, 405, 410, 414, 501):
browser = max(0, int((date - lastmod).total_seconds() / 10))
heuristic = True
browser = browser or 0
shared = 0 if "private" in cc else cc.get("s-maxage", browser)
if "no-cache" in cc:
browser_eff, shared_eff = 0, 0
else:
browser_eff, shared_eff = browser, shared
validator = "etag" in h or "last-modified" in h
personal = bool(cookies) or auth
if no_store and any(k in cc for k in ("max-age", "s-maxage", "public", "immutable")):
flag("NO_STORE_CONFLICT", "no-store overrides the other directives; remove the extras so intent is clear")
if cookies and ("public" in cc or "s-maxage" in cc) and not no_store:
flag("PUBLIC_WITH_COOKIE", "response sets a cookie but allows shared caches; a CDN may serve one user's cookie to others")
if auth and shared > 0 and ("public" in cc or "s-maxage" in cc) and kind in ("api", "html", "other"):
flag("AUTH_SHARED_CACHE", "authenticated request with a response that shared caches may store; personal data can leak across users")
elif personal and kind in ("api", "html", "other") and not no_store and "private" not in cc \
and not any(f["code"] == "PUBLIC_WITH_COOKIE" for f in flags):
flag("PERSONAL_NOT_PRIVATE", "personalized response without private or no-store")
vary = [v.strip().lower() for v in h.get("vary", "").split(",") if v.strip()]
if "*" in vary:
flag("VARY_STAR", "Vary: * makes the response effectively uncacheable")
frag = [v for v in vary if v in ("user-agent", "cookie", "referer")]
if frag and shared > 0:
flag("VARY_FRAGMENTS", f"Vary on {', '.join(frag)} splits the CDN cache into many copies; vary on a normalized header instead")
if kind == "html" and browser_eff > 300:
flag("HTML_LONG_TTL", f"HTML cached {fmt_s(browser_eff)} without revalidation; users keep old pages that point to deleted assets after a deploy")
if kind == "hashed-asset" and browser_eff < 30 * 86400 and not no_store:
flag("HASHED_SHORT_TTL", f"content-hashed file cached only {fmt_s(browser_eff)}; it can be cached for a year with immutable")
if "immutable" in cc and not hashed:
flag("IMMUTABLE_UNHASHED", "immutable on a URL without a content hash; browsers will not pick up changes until max-age expires")
if kind in ("asset", "image", "font") and (no_store or "no-cache" in cc) and not personal:
flag("ASSET_NO_CACHING", "static file is never reused from cache; every page view downloads or revalidates it")
if ("no-cache" in cc or browser_eff == 0) and not no_store and not validator and status == 200:
flag("NO_VALIDATOR", "must revalidate but has no ETag or Last-Modified, so every check downloads the full body")
if heuristic:
flag("HEURISTIC_ONLY", f"no Cache-Control or Expires; caches guess {fmt_s(browser)} from Last-Modified")
if "cache-control" not in h and expires is not None:
flag("EXPIRES_ONLY", "only the legacy Expires header; add Cache-Control max-age")
if "cache-control" not in h and "pragma" in h:
flag("PRAGMA_ONLY", "Pragma: no-cache is a request header and has no effect on responses; use Cache-Control")
if status >= 400 and max(browser_eff, shared_eff) > 300:
flag("ERROR_CACHED", f"status {status} cached for {fmt_s(max(browser_eff, shared_eff))}; a brief error becomes a long outage")
rec_kind = "personal" if personal and kind in ("api", "html", "other") else kind
return {"label": block["label"], "status": status, "kind": kind, "hashed": hashed,
"cache_control": h.get("cache-control"), "browser_ttl_s": browser_eff, "shared_ttl_s": shared_eff,
"revalidate": "no-cache" in cc or "must-revalidate" in cc, "validator": validator,
"stale_while_revalidate_s": cc.get("stale-while-revalidate"), "flags": flags,
"recommended": RECOMMEND[rec_kind]}
def fmt_s(s):
if s is None:
return "-"
for unit, n in (("d", 86400), ("h", 3600), ("m", 60)):
if s >= n:
v = s / n
return f"{v:.0f}{unit}" if v == int(v) else f"{v:.1f}{unit}"
return f"{s}s"
def audit(text):
items = [review(b) for b in parse_blocks(text)]
return {"items": items, "high_flags": sum(1 for i in items for f in i["flags"] if f["severity"] == "high")}
def to_markdown(r):
out = ["# HTTP cache header review", "",
"| Response | Status | Kind | Browser TTL | CDN TTL | Revalidate | Validator | Flags |",
"|---|---|---|---|---|---|---|---|"]
for i in r["items"]:
out.append(f"| {i['label']} | {i['status']} | {i['kind']} | {fmt_s(i['browser_ttl_s'])} | {fmt_s(i['shared_ttl_s'])} | "
f"{'yes' if i['revalidate'] else 'no'} | {'yes' if i['validator'] else 'no'} | {', '.join(f['code'] for f in i['flags']) or '-'} |")
out += ["", "## Findings"]
n = 0
for sev in ("high", "medium", "low"):
for i in r["items"]:
for f in i["flags"]:
if f["severity"] == sev:
n += 1
out.append(f"- **{sev.upper()} {f['code']}** {i['label']}: {f['detail']}")
if not n:
out.append("- No findings.")
out += ["", "## Suggested Cache-Control"]
for i in r["items"]:
if i["flags"]:
out.append(f"- {i['label']}: `{i['recommended']}` (now: `{i['cache_control'] or 'none'}`)")
return "\n".join(out)
def self_test():
cases = []
def ok(name, cond):
cases.append((name, bool(cond)))
def one(url, *lines):
return review(parse_blocks("### GET " + url + "\nHTTP/1.1 200 OK\n" + "\n".join(lines))[0])
def codes(item):
return {f["code"] for f in item["flags"]}
ok("parse max-age", parse_cc("public, max-age=600")[0] == {"public": True, "max-age": 600})
ok("bad max-age reported", parse_cc("max-age=10m")[1])
ok("unknown directive reported", parse_cc("maxage=60")[1])
ok("hashed js detected", kind_of("https://x/app.3f9a1c7b.js", "") == ("hashed-asset", True))
ok("unhashed css", kind_of("https://x/styles.css", "text/css") == ("asset", False))
ok("html by content type", kind_of("https://x/", "text/html; charset=utf-8")[0] == "html")
ok("api by json", kind_of("https://x/api/cart", "application/json")[0] == "api")
i = one("https://x/app.3f9a1c7b.js", "Cache-Control: public, max-age=31536000, immutable", "ETag: \"a\"")
ok("ideal hashed asset clean", not codes(i) and i["browser_ttl_s"] == 31536000)
i = one("https://x/app.3f9a1c7b.js", "Cache-Control: public, max-age=3600")
ok("hashed short ttl", "HASHED_SHORT_TTL" in codes(i))
i = one("https://x/main.js", "Cache-Control: public, max-age=31536000, immutable")
ok("immutable unhashed", "IMMUTABLE_UNHASHED" in codes(i))
i = one("https://x/", "Content-Type: text/html", "Cache-Control: max-age=86400")
ok("html long ttl", "HTML_LONG_TTL" in codes(i))
i = one("https://x/", "Content-Type: text/html", "Cache-Control: no-cache", "ETag: \"1\"")
ok("html no-cache with etag clean", not codes(i) and i["browser_ttl_s"] == 0)
i = one("https://x/", "Content-Type: text/html", "Cache-Control: no-cache")
ok("no validator", "NO_VALIDATOR" in codes(i))
i = one("https://x/login", "Content-Type: text/html", "Cache-Control: public, max-age=600", "Set-Cookie: sid=1")
ok("public with cookie", "PUBLIC_WITH_COOKIE" in codes(i))
i = review(parse_blocks("### GET https://x/api/me\n> Authorization: Bearer t\nHTTP/2 200\ncontent-type: application/json\ncache-control: public, s-maxage=300")[0])
ok("auth shared cache", "AUTH_SHARED_CACHE" in codes(i) and i["shared_ttl_s"] == 300)
i = review(parse_blocks("### GET https://x/api/me\n> Cookie: sid=1\nHTTP/2 200\ncontent-type: application/json\ncache-control: max-age=60")[0])
ok("personal not private", "PERSONAL_NOT_PRIVATE" in codes(i))
i = one("https://x/api/me", "Content-Type: application/json", "Cache-Control: private, max-age=60")
ok("private hides from cdn", i["shared_ttl_s"] == 0 and i["browser_ttl_s"] == 60)
i = one("https://x/a.css", "Cache-Control: no-store, max-age=60")
ok("no-store conflict and asset no caching", {"NO_STORE_CONFLICT", "ASSET_NO_CACHING"} <= codes(i))
i = one("https://x/a.css", "Cache-Control: public, max-age=600", "Vary: *")
ok("vary star", "VARY_STAR" in codes(i))
i = one("https://x/a.css", "Cache-Control: public, max-age=600", "Vary: Accept-Encoding, User-Agent")
ok("vary user-agent fragments", "VARY_FRAGMENTS" in codes(i))
i = one("https://x/logo.png", "Date: Wed, 21 Oct 2026 10:00:00 GMT", "Last-Modified: Mon, 11 Oct 2026 10:00:00 GMT")
ok("heuristic 10% of 10 days = 1 day", "HEURISTIC_ONLY" in codes(i) and i["browser_ttl_s"] == 86400)
i = one("https://x/logo.png", "Date: Wed, 21 Oct 2026 10:00:00 GMT", "Expires: Wed, 21 Oct 2026 11:00:00 GMT")
ok("expires only gives 1h", "EXPIRES_ONLY" in codes(i) and i["browser_ttl_s"] == 3600)
i = one("https://x/", "Content-Type: text/html", "Pragma: no-cache")
ok("pragma only", "PRAGMA_ONLY" in codes(i))
i = review(parse_blocks("### GET https://x/a.css\nHTTP/1.1 503 Service Unavailable\ncache-control: public, max-age=3600")[0])
ok("error cached", "ERROR_CACHED" in codes(i))
ok("repeated cache-control merged", parse_blocks("### GET https://x/a\nHTTP/1.1 200\ncache-control: public\ncache-control: max-age=5")[0]["headers"]["cache-control"] == "public, max-age=5")
try:
parse_blocks("HTTP/1.1 200 OK\n")
ok("missing ### rejected", False)
except CacheError:
ok("missing ### rejected", True)
ok("fmt_s", fmt_s(31536000) == "365d" and fmt_s(600) == "10m" and fmt_s(45) == "45s" and fmt_s(699840) == "8.1d")
passed = sum(c for _, c in cases)
for name, c in cases:
print(("PASS " if c else "FAIL ") + name)
print(f"{passed}/{len(cases)} passed")
return 0 if passed == len(cases) else 1
def main(argv=None):
ap = argparse.ArgumentParser(description="Review HTTP caching headers.")
ap.add_argument("file", nargs="?", help="responses text file ('-' for stdin)")
ap.add_argument("--json", action="store_true")
ap.add_argument("--self-test", action="store_true")
a = ap.parse_args(argv)
if a.self_test:
return self_test()
if not a.file:
ap.error("responses file required (or --self-test)")
try:
text = sys.stdin.read() if a.file == "-" else open(a.file, encoding="utf-8").read()
r = audit(text)
except (OSError, CacheError) as e:
print(f"error: {e}", file=sys.stderr)
return 2
print(json.dumps(r, indent=2) if a.json else to_markdown(r))
return 1 if r["high_flags"] else 0
if __name__ == "__main__":
sys.exit(main())Opinionated preferences for managing client and server state in React apps.
# React State Management taste - Start with local useState and lift state only when two siblings truly need it. Confidence: 0.95 - Treat server data as a cache and manage it with TanStack Query instead of a global store. Confidence: 0.90 - Keep URL-worthy state such as filters, tabs and pagination in search params. Confidence: 0.90 - Reach for Zustand when shared client state outgrows a single component tree. Confidence: 0.80 - Avoid Redux for new projects unless the team already depends on its devtools and middleware. Confidence: 0.70 - Use React Context for rarely changing values like theme, locale and the current user, not for fast-changing data. Confidence: 0.90 - Derive values during render instead of syncing them into extra state with useEffect. Confidence: 0.95 - Model complex local state with useReducer and a discriminated union of actions. Confidence: 0.80 - Represent async status as one union like idle, loading, success and error rather than several booleans. Confidence: 0.85 - Keep form state in React Hook Form with a zod schema instead of hand-rolled useState per field. Confidence: 0.80 - Select the smallest slice of a store in each component to avoid needless re-renders. Confidence: 0.85 - Store ids in state and look up the full objects, instead of duplicating nested data. Confidence: 0.80 - Use optimistic updates for quick user actions and roll back on error. Confidence: 0.75 - Never mutate state objects in place; return new objects or use Immer for deep updates. Confidence: 0.90 - Keep persisted state small and versioned when saving it to localStorage. Confidence: 0.75 - Reset component state by changing its key instead of writing reset effects. Confidence: 0.80 - Colocate stores with the feature that owns them rather than in one global store folder. Confidence: 0.75 - Type every store and context value explicitly and avoid any in state shapes. Confidence: 0.90
Reviews a schema and slow SQL queries, proposes composite indexes in the right column order (equality, sort, range) with covering columns and tradeoffs, flags non-sargable filters like functions on columns and leading-wildcard LIKE, and warns about duplicate, redundant, and low-selectivity indexes. Use when a user shares a slow query, EXPLAIN output, or schema and asks "what index do I need?" or "too many indexes?". Includes a tested stdlib Python helper.
---
name: sql-index-recommendation-reviewer
description: Reviews a schema and slow SQL queries, proposes composite indexes in the right column order (equality, sort, range) with covering columns and tradeoffs, flags non-sargable filters like functions on columns and leading-wildcard LIKE, and warns about duplicate, redundant, and low-selectivity indexes. Use when a user shares a slow query, EXPLAIN output, or schema and asks "what index do I need?" or "too many indexes?". Includes a tested stdlib Python helper.
---
# SQL Index Recommendation Reviewer
You help developers make slow queries fast without burying their tables in indexes. You read the schema and the query the way a database engineer would: which columns are compared with equality, which with ranges, what the query sorts by, what it joins on, and which indexes already exist. You propose the smallest set of indexes that serves the workload, in the right column order, and you are honest that only EXPLAIN on real data can confirm it.
## Files in this skill
- `scripts/suggest_indexes.py` - parses CREATE TABLE / CREATE INDEX statements and SELECT, UPDATE, and DELETE queries (subqueries and CTE bodies separately), then prints candidate indexes with DDL, the queries each one serves, covering columns, overlaps, and schema findings (Python 3 standard library only; no database connection)
- `references/indexing-rules.md` - column order, covering indexes, partial and expression indexes, sargability, and over-indexing rules
- `references/explain-reading-guide.md` - how to read EXPLAIN in PostgreSQL, MySQL, and SQLite to confirm or reject a suggestion
- `templates/index-review.md` - the review report to return
- `examples/example-shop-orders-review.md` - a worked review of an online shop's slow queries
## Workflow
### 1. Collect the facts
Ask, or assume and say so:
- The engine and version (PostgreSQL, MySQL/MariaDB, SQLite, SQL Server), and the schema with existing indexes (`\d table`, `SHOW CREATE TABLE`, or the migration files).
- The slow queries exactly as the app sends them, with typical parameter values, how often each runs, and how slow it is.
- Table sizes (rows), how write-heavy each table is, and any EXPLAIN or EXPLAIN ANALYZE output.
- Constraints: can the team build indexes online, disk space, and replication lag concerns.
### 2. Run the helper
```bash
python3 scripts/suggest_indexes.py --schema schema.sql slow-queries.sql
python3 scripts/suggest_indexes.py all-in-one.sql --dialect mysql
python3 scripts/suggest_indexes.py --schema schema.sql - --json < query.sql
python3 scripts/suggest_indexes.py --schema schema.sql queries.sql --strict # exit 1 on non-sargable filters or duplicate indexes
```
The helper is a heuristic parser, not a planner: it does not know row counts, data distribution, or which plan the database will choose. It can miss predicates in complex SQL (it lists them as "not understood"). Read every query yourself and treat each suggestion as a candidate to test. If you cannot run the script, apply `references/indexing-rules.md` by hand in the same order.
### 3. Decide
1. Fix the query before adding an index: rewrite non-sargable filters (functions on columns, arithmetic, leading-wildcard LIKE, OR across columns) so an index can be used at all.
2. For each query, choose column order: equality columns (most selective first when you know it), then ORDER BY or GROUP BY columns if the query sorts with LIMIT, then one range column.
3. Merge: one composite index can serve several queries when they share its leftmost columns. Prefer extending an existing index over adding a new one.
4. Add covering (INCLUDE) columns only for hot, read-heavy queries, and keep them few.
5. Remove before adding: drop duplicate and redundant-prefix indexes after checking usage statistics (`pg_stat_user_indexes`, `sys.schema_unused_indexes`).
6. Count the cost: every index slows inserts and updates of its columns and uses disk and memory. Write-heavy tables deserve fewer, broader indexes.
### 4. Deliver
Fill in `templates/index-review.md`: per-query diagnosis, the recommended DDL in build order with the queries each serves, indexes to drop, query rewrites, tradeoffs, and how to verify with EXPLAIN before and after (see `references/explain-reading-guide.md`). Follow the style of `examples/example-shop-orders-review.md`.
## Rules
- Never claim a speed-up without saying how to measure it; give expected plan changes ("index scan instead of sequential scan and sort"), not invented timings.
- Use safe build commands for production: `CREATE INDEX CONCURRENTLY` in PostgreSQL, online DDL (`ALGORITHM=INPLACE, LOCK=NONE`) in MySQL, and a maintenance window for SQLite.
- Do not recommend an index on a low-selectivity column alone (status, booleans); use it inside a composite or as a partial index condition.
- Keep primary keys and unique constraints; never suggest dropping them to remove "redundancy".
- Tell the user to build one index at a time and compare plans, and to remove indexes that EXPLAIN never uses.
FILE:references/indexing-rules.md
# Indexing rules
The rules the helper applies, plus the judgment it cannot make. Examples use PostgreSQL syntax unless noted.
## 1. Column order in a composite index
A B-tree index is sorted by its first column, then the second, and so on. A query can seek on a leftmost run of columns compared with equality, then use one more column for a range or for sorting.
Order: **equality columns, then sort columns, then one range column**.
```sql
-- WHERE customer_id = ? AND status = 'paid' ORDER BY created_at DESC LIMIT 20
CREATE INDEX ON orders (customer_id, status, created_at);
```
- Among equality columns, put the one used by the most queries first so the index serves them all; selectivity matters less than reuse once all of them are equalities.
- After a range column (`>`, `<`, `BETWEEN`, `LIKE 'abc%'`), later columns cannot be used for seeking, only for filtering inside the index.
- A sort can use the index only if every ORDER BY column comes from the index in the same order and directions are all the same (or all reversed). Mixed directions need a matching index definition (`created_at DESC, id ASC`).
- With a range and an ORDER BY on a different column, the database must choose: seek with the range and sort, or walk the sort order and filter. With LIMIT, walking the sort order often wins.
## 2. Leftmost prefix and merging
An index on `(a, b, c)` serves queries on `a`, on `a, b`, and on `a, b, c`, but not on `b` or `c` alone. Two candidates where one is a leftmost prefix of the other become one index. An existing index `(a)` is redundant once `(a, b)` exists, unless it is unique, partial, or much smaller and very hot.
## 3. Joins and foreign keys
- Index the column on the side that is looked up: usually the foreign key (`orders.customer_id`). The primary key side is already indexed.
- PostgreSQL does not index foreign keys automatically (MySQL InnoDB does). Missing FK indexes also make deletes on the parent table slow.
- A join column plus that table's own filters can form one composite: `(customer_id, created_at)`.
## 4. Covering indexes
If the index holds every column the query reads, the database can skip the table (index-only scan).
- PostgreSQL 11+ and SQL Server: `INCLUDE (col, ...)` stores extra columns without sorting by them.
- MySQL and SQLite: append the columns to the key; InnoDB secondary indexes already carry the primary key.
- Use it for hot, read-mostly queries with few selected columns. Wide covering indexes are big and slow to write.
- PostgreSQL index-only scans also need a well-vacuumed table (visibility map).
## 5. Partial and expression indexes
- Partial (PostgreSQL, SQLite; filtered index in SQL Server): `CREATE INDEX ON orders (created_at) WHERE status = 'paid' AND shipped_at IS NULL;` Tiny and fast when the condition matches few rows. The query must repeat the same condition.
- Expression: `CREATE INDEX ON users (lower(email));` serves `WHERE lower(email) = ?`. MySQL 8 supports functional indexes `((lower(email)))` or a generated column with an index.
## 6. Sargability: filters an index cannot use
| Pattern | Problem | Fix |
|---|---|---|
| `WHERE date(created_at) = '2026-10-12'` | function on the column | `created_at >= '2026-10-12' AND created_at < '2026-10-13'` |
| `WHERE YEAR(updated_at) = 2026` | function on the column | range on the column |
| `WHERE price * 1.2 > 100` | arithmetic on the column | `price > 100 / 1.2` |
| `WHERE name LIKE '%lamp%'` | leading wildcard | full-text search, or `pg_trgm` GIN index |
| `WHERE lower(name) = ?` | function | expression index on `lower(name)` or a case-insensitive collation |
| `WHERE a = 1 OR b = 2` | OR across columns | `UNION` of two indexed queries, or one index per column (bitmap OR in PostgreSQL) |
| `WHERE status <> 'done'`, `NOT IN` | negative filter | positive list `IN (...)` or a partial index |
| `WHERE id = '42'` on an integer column | implicit cast (MySQL may skip the index on string columns compared to numbers) | compare with the right type |
## 7. Over-indexing
- Every index is updated on INSERT, on DELETE, and on UPDATE of its columns; it also uses disk, memory (buffer cache), and backup and replication bandwidth.
- Duplicates (same columns, same condition) are pure cost: drop one.
- Single-column indexes on low-selectivity columns (booleans, status, type) are rarely used; the planner prefers a scan when a value matches more than about 5 to 20 percent of rows. Use them inside composites or as partial-index conditions.
- As a rule of thumb, more than 5 or 6 indexes on a write-heavy table deserves a review; read-mostly tables can carry more.
- Find unused indexes before dropping: PostgreSQL `pg_stat_user_indexes.idx_scan = 0` (since the last stats reset, on every replica), MySQL `sys.schema_unused_indexes`. Drop with `DROP INDEX CONCURRENTLY` in PostgreSQL.
## 8. Building safely
- PostgreSQL: `CREATE INDEX CONCURRENTLY` avoids blocking writes; it cannot run inside a transaction and leaves an INVALID index on failure (drop and retry).
- MySQL 8: `ALTER TABLE ... ADD INDEX ..., ALGORITHM=INPLACE, LOCK=NONE`; watch replication lag on large tables.
- SQLite: index builds lock the database; run during low traffic.
- Build one index at a time, check the plan, then the next.
FILE:references/explain-reading-guide.md
# Reading EXPLAIN to confirm an index
Always compare the plan before and after, on production-like data and with realistic parameter values. Small test tables make the planner choose scans that are right for small tables.
## PostgreSQL
```sql
EXPLAIN (ANALYZE, BUFFERS) SELECT ...; -- runs the query; wrap writes in BEGIN ... ROLLBACK
```
| Plan node | Meaning |
|---|---|
| Seq Scan | reads the whole table; fine for small tables or when most rows match |
| Index Scan | seeks the index, then reads matching table rows |
| Index Only Scan | answered from the index; check "Heap Fetches" is low (vacuum if not) |
| Bitmap Index Scan + Bitmap Heap Scan | collects many matches, then reads pages in order; common for medium selectivity and OR |
| Sort (with "external merge") | sorting spilled to disk; an index in ORDER BY order can remove it |
| Rows Removed by Filter | rows read and thrown away; high numbers mean the index does not cover the filter |
Look at: actual time of the top node, rows estimated versus actual (a 10x gap means stale statistics: run `ANALYZE table`), and shared hit/read buffers. Confirm a new index is used with `pg_stat_user_indexes.idx_scan` after a day of traffic.
## MySQL 8
```sql
EXPLAIN FORMAT=TREE SELECT ...;
EXPLAIN ANALYZE SELECT ...; -- 8.0.18+, runs the query
```
In classic `EXPLAIN` output check: `type` (ALL = full scan, ref/eq_ref/range = index use, index = full index scan), `key` (the index chosen), `rows` (estimate), and `Extra` ("Using index" = covering, "Using filesort" = extra sort, "Using temporary" = temporary table for GROUP BY or DISTINCT). Refresh statistics with `ANALYZE TABLE t`.
## SQLite
```sql
EXPLAIN QUERY PLAN SELECT ...;
```
"SCAN t" is a full scan; "SEARCH t USING INDEX idx (a=? AND b>?)" shows which columns seek; "USING COVERING INDEX" means no table access; "USE TEMP B-TREE FOR ORDER BY" means an extra sort. Run `ANALYZE;` so the planner has statistics.
## What success looks like
- The slow query's plan switches from a full scan plus sort to an index (only) scan with no sort, and the rows read drop close to the rows returned.
- Writes on the table do not get noticeably slower (check p95 insert and update latency after deploying).
- No other important query changed plan for the worse; run the top queries by total time (`pg_stat_statements`, MySQL performance schema digest tables) before and after.
## When the index is not used
1. Statistics are stale: run ANALYZE.
2. The filter is not sargable (see indexing-rules.md section 6).
3. The value matches too many rows; the planner is right to scan.
4. Column types or collations differ between the query and the column (implicit cast).
5. A parameterized query uses a generic plan; test with the real prepared statement.
6. The index columns are in the wrong order for the query.
FILE:templates/index-review.md
# Index review: app_or_service
**Engine:** engine_and_version | **Tables:** tables_with_row_counts | **Write load:** write_profile
**Helper:** n_queries queries analyzed, n_suggested candidates, n_findings schema findings
## Summary
Two or three sentences: the main cause of slowness, the indexes to add and drop, and the expected plan change.
## Per-query diagnosis
| Query | Runs | Now (plan / time) | Problem | Fix |
|---|---|---|---|---|
| Q1 | per_minute | Seq Scan + Sort | | |
## Query rewrites (do these first)
```sql
-- before
-- after
```
## Indexes to add (build in this order)
| # | DDL | Serves | Why this column order | Cost |
|---|---|---|---|---|
| 1 | | | | |
## Indexes to drop (after checking usage)
| Index | Reason | Check first |
|---|---|---|
| | duplicate / redundant prefix / unused / low selectivity | `idx_scan` on primary and replicas |
## Net effect per table
| Table | Indexes before | After | Note |
|---|---|---|---|
## How to verify
1. Capture `EXPLAIN (ANALYZE, BUFFERS)` for each query before.
2. Build one index (`CONCURRENTLY` / online DDL), run `ANALYZE`, capture the plan again.
3. Expect: (plan change per query).
4. Watch write latency and replication lag for a day; then drop the indexes listed above.
## Caveats
- Suggestions come from query text and schema only; row counts and data skew can change the best choice.
FILE:examples/example-shop-orders-review.md
# Example: index review for an online shop
## User request
"Our PostgreSQL 16 shop database is getting slow. orders has 12 million rows and gets about 40 inserts a second, customers has 900k rows, products 20k. Here are the schema and the six queries that show up in pg_stat_statements. What indexes should we add, and do we have too many already?"
## Helper run
```
$ python3 scripts/suggest_indexes.py --schema shop-schema.sql slow-queries.sql
Schema: 4 table(s), 12 existing index(es) incl. keys | dialect: postgres
Queries analyzed: 7
Q1 SELECT: SELECT o.id, o.total, o.created_at FROM orders o WHERE o.customer_id = $1 AND o.status = 'paid' ORDER BY o.cre...
equality: orders.customer_id (=), orders.status (=)
order by: orders.created_at DESC (LIMIT)
Q2 SELECT: SELECT c.email, count(*) AS orders FROM customers c JOIN orders o ON o.customer_id = c.id WHERE c.country = 'D...
equality: customers.country (=)
range: orders.created_at (range)
joins: orders.customer_id = customers.id
group by: customers.email
Q3 SELECT: SELECT * FROM products WHERE lower(name) LIKE '%lamp%'
WARN non-sargable: lower(name) in the WHERE clause hides the column from a normal index; ... the LIKE pattern '%lamp%' also starts with a wildcard, so only full-text search or a trigram index can help
Q4 SELECT: ... WHERE oi.order_id IN (SELECT id FROM orders WHERE customer_id = 42 AND created_at > now() - interval '30 days')
note: subquery analyzed as Q5
Q6 UPDATE: UPDATE orders SET status = 'shipped', shipped_at = now() WHERE status = 'paid' AND shipped_at IS NULL AND crea...
Q7 SELECT: SELECT id FROM customers WHERE email = 'ann@example.com' OR phone = '+491701234567'
WARN OR across different columns (...): one composite index cannot serve both sides; consider UNION ALL of two indexed queries or one index per side
Suggested indexes (4):
1. CREATE INDEX CONCURRENTLY idx_customers_country_email ON customers (country, email);
2. CREATE INDEX CONCURRENTLY idx_orders_customer_id_created_at ON orders (customer_id, created_at);
serves: Q2, Q5 | overlap: same leading column as #3
3. CREATE INDEX CONCURRENTLY idx_orders_customer_id_status_created_at ON orders (customer_id, status, created_at) INCLUDE (id, total);
serves: Q1 | overlap: same leading column as #2
4. CREATE INDEX CONCURRENTLY idx_orders_status_shipped_at_created_at ON orders (status, shipped_at, created_at);
serves: Q6 | alternative: ... ON orders (status, created_at) WHERE shipped_at IS NULL;
Schema findings (5):
WARN redundant-prefix customers: idx_customers_country (country) is a leftmost prefix of idx_customers_country_created ...
WARN low-selectivity customers: idx_customers_active indexes only 'is_active' ...
HIGH duplicate-index orders: idx_orders_created and orders_created_at_idx have the same columns (created_at); drop one
WARN low-selectivity orders: idx_orders_status indexes only 'status' ...
WARN many-indexes orders: 4 existing + 3 suggested = 7 indexes (limit 6) ...
```
## Review (filled template, shortened)
**Summary:** orders has no index that starts with customer_id, so the order history page (Q1) and the recent-orders lookup (Q5) scan millions of rows, and two of its four indexes are a duplicate and a low-selectivity status index. Add one composite and one partial index on orders, a phone index and a trigram index elsewhere, and drop three indexes: orders ends with the same count of 4 but every one is useful.
| Query | Problem | Fix |
|---|---|---|
| Q1 order history | no index on customer_id; sort on created_at | (customer_id, created_at) with status and total included: newest rows for the customer, status filtered inside the index, LIMIT stops after 20 |
| Q2 country report | join needs orders.customer_id; customers.country is already served by idx_customers_country_created | same orders index; no new customers index (the helper's #1 only helps the GROUP BY, and the report runs once a night) |
| Q3 product search | `lower(name) LIKE '%lamp%'` cannot use a B-tree | pg_trgm GIN index on lower(name) |
| Q4/Q5 recent items | subquery needs (customer_id, created_at); order_items PK (order_id, product_id) serves the IN | same orders index |
| Q6 shipping job | scans by status | partial index on created_at for paid, unshipped orders only |
| Q7 support lookup | OR across email and phone | UNION of two lookups; email is unique already, add a phone index |
Why not the helper's #3 as well: #2 and #3 share customer_id, and on a table with 40 inserts a second one index is better than two. The user confirmed that about 95 percent of orders are paid, so Q1 throws away few rows, and (customer_id, created_at) with status in INCLUDE keeps Q1 fast. If the share of non-paid orders grows, switch to #3's column order.
**Indexes to add (in this order):**
```sql
CREATE INDEX CONCURRENTLY idx_orders_customer_created
ON orders (customer_id, created_at) INCLUDE (id, status, total); -- Q1, Q2, Q5
CREATE INDEX CONCURRENTLY idx_orders_paid_unshipped
ON orders (created_at) WHERE status = 'paid' AND shipped_at IS NULL; -- Q6, holds only paid, unshipped orders
CREATE INDEX CONCURRENTLY idx_customers_phone ON customers (phone); -- Q7 after the rewrite
CREATE EXTENSION IF NOT EXISTS pg_trgm;
CREATE INDEX CONCURRENTLY idx_products_name_trgm
ON products USING gin (lower(name) gin_trgm_ops); -- Q3, query unchanged
```
**Query rewrite (Q7):**
```sql
SELECT id FROM customers WHERE email = 'ann@example.com'
UNION
SELECT id FROM customers WHERE phone = '+491701234567';
```
**Indexes to drop (after checking `pg_stat_user_indexes.idx_scan` on the primary and both replicas):**
| Index | Reason |
|---|---|
| orders_created_at_idx | duplicate of idx_orders_created |
| idx_orders_status | low selectivity; Q6 now uses the partial index |
| idx_customers_country | leftmost prefix of idx_customers_country_created |
| idx_customers_active (check) | boolean; keep only if idx_scan shows real use |
**Net effect:** orders 4 -> 4 indexes (two replaced by better ones), customers 5 -> 5 (one dropped, phone added; 4 if is_active goes too), products 2 -> 3.
**Recheck with the helper** (schema after the change, queries after the rewrite; query numbers follow the new file, so Q3 is the old Q5 and Q4/Q5 are the two UNION branches):
```
$ python3 scripts/suggest_indexes.py --schema shop-schema-after.sql shop-queries-after.sql --no-covering
Already served by existing indexes (5):
customers (email) -> customers_email_key (Q4)
customers (id, country) -> customers_pkey (Q2)
customers (phone) -> idx_customers_phone (Q5)
orders (created_at) -> idx_orders_created (Q2)
orders (customer_id, created_at) -> idx_orders_customer_created (Q2, Q3)
```
The helper still lists (customer_id, status, created_at) for Q1 and (country, email) for Q2; both were rejected on purpose for the reasons above. There are no duplicate or redundant-prefix findings left.
**How to verify:** before and after each build, run `EXPLAIN (ANALYZE, BUFFERS)` for Q1 with a real customer id. Expect "Index Scan using idx_orders_customer_created" (or Index Only Scan) with no Sort node and about 20 rows read instead of a Bitmap Heap Scan over thousands. Watch insert latency on orders for a day before dropping the old indexes.
FILE:scripts/suggest_indexes.py
#!/usr/bin/env python3
"""Suggest candidate indexes for slow SQL queries from a schema and the query text (no database needed).
Usage:
python3 suggest_indexes.py --schema schema.sql queries.sql [options]
python3 suggest_indexes.py all-in-one.sql (CREATE statements and queries in one file)
python3 suggest_indexes.py --schema schema.sql - < slow.sql
Options:
--schema FILE CREATE TABLE / CREATE INDEX statements (may also be inside the query file)
--dialect NAME postgres (default), mysql, or sqlite; changes INCLUDE and online-build hints
--max-indexes N warn when a table would have more than N indexes (default 6)
--no-covering do not suggest covering (INCLUDE) columns
--json print the result as JSON
--strict exit 1 if any query has a non-sargable predicate or the schema has duplicate indexes
What it does: lightweight parsing of SELECT, UPDATE, and DELETE statements (subqueries are analyzed
separately) to find equality filters, range filters, join columns, ORDER BY and GROUP BY columns,
and selected columns per table. It builds composite candidates (equality columns, then sort, then
range), merges candidates that are prefixes of each other, skips those already served by an existing
index, and reports duplicate and redundant indexes, low-selectivity single-column indexes, and tables
with many indexes. It does not know row counts or data distribution: confirm every suggestion with
EXPLAIN on real data.
Exit codes: 0 ok, 1 --strict findings, 2 usage or read error.
Python 3 standard library only.
"""
import json
import re
import signal
import sys
if hasattr(signal, "SIGPIPE"):
signal.signal(signal.SIGPIPE, signal.SIG_DFL) # quiet exit when piped into head
KEYWORDS = set("""select from where and or not in is null like ilike between join inner left right full outer cross on
using group by order having limit offset as asc desc distinct union all exists case when then else end update set
delete insert into values returning with true false interval current_date current_timestamp now lateral natural
fetch first rows only for share nowait skip locked""".split())
LOW_CARD = re.compile(r"^(is_|has_|can_|should_)|^(status|state|type|kind|flag|active|enabled|deleted|archived|gender|"
r"visible|published|verified|priority|level|tier|role)$", re.I)
CLAUSE_END = r"(?=\b(?:where|group\s+by|order\s+by|having|limit|offset|union|returning|for\s+update|window)\b|$)"
class UsageError(Exception):
pass
# ---------------------------------------------------------------- text helpers
def strip_comments(sql):
sql = re.sub(r"/\*.*?\*/", " ", sql, flags=re.S)
return re.sub(r"--[^\n]*", " ", sql)
def split_statements(sql):
out, buf, quote = [], [], None
for ch in sql:
if quote:
buf.append(ch)
if ch == quote:
quote = None
continue
if ch in "'\"`":
quote = ch
if ch == ";":
out.append("".join(buf))
buf = []
else:
buf.append(ch)
out.append("".join(buf))
return [s.strip() for s in out if s.strip()]
def unquote_idents(sql):
sql = re.sub(r'"([A-Za-z_][\w$]*)"', r"\1", sql)
sql = re.sub(r"`([A-Za-z_][\w$]*)`", r"\1", sql)
return re.sub(r"\[([A-Za-z_][\w$]*)\]", r"\1", sql)
def mask_strings(sql):
"""Replace string literals with placeholders, remembering LIKE patterns."""
lits = []
def rep(m):
lits.append(m.group(0)[1:-1])
return f" __lit{len(lits) - 1}__ "
return re.sub(r"'(?:[^']|'')*'", rep, sql), lits
def split_top(text, sep_regex):
"""Split on a keyword at parenthesis depth 0."""
parts, depth, last = [], 0, 0
for m in re.finditer(r"\(|\)|" + sep_regex, text, flags=re.I):
tok = m.group(0)
if tok == "(":
depth += 1
elif tok == ")":
depth -= 1
elif depth == 0:
parts.append(text[last:m.start()])
last = m.end()
parts.append(text[last:])
return [p.strip() for p in parts if p.strip()]
def split_and(text):
"""Split on top-level AND, keeping 'x BETWEEN a AND b' together."""
parts = split_top(text, r"\band\b")
out = []
for part in parts:
if out and re.search(r"\bbetween\s+[^\s]+$", out[-1], re.I):
out[-1] = f"{out[-1]} AND {part}"
else:
out.append(part)
return out
def extract_subqueries(sql):
"""Pull out innermost (SELECT ...) blocks; return (outer_sql, [subqueries])."""
subs = []
pattern = re.compile(r"\(\s*(select\b[^()]*(?:\([^()]*\)[^()]*)*)\)", re.I)
while True:
m = pattern.search(sql)
if not m:
break
subs.append(m.group(1))
sql = sql[:m.start()] + " __subq__ " + sql[m.end():]
return sql, subs
# ---------------------------------------------------------------- schema
def parse_columns_list(text):
return [re.sub(r"\s+(asc|desc)\b.*$", "", c.strip(), flags=re.I).strip().lower()
for c in split_top(text, r",")]
def parse_schema(statements):
tables, indexes = {}, []
for st in statements:
s = unquote_idents(strip_comments(st)).strip()
m = re.match(r"create\s+table\s+(?:if\s+not\s+exists\s+)?([\w.]+)\s*\((.*)\)\s*[^)]*$", s, re.I | re.S)
if m:
name = m.group(1).split(".")[-1].lower()
cols, pk = [], None
for part in split_top(m.group(2), r","):
p = part.strip()
low = p.lower()
c = re.match(r"(?:constraint\s+\w+\s+)?primary\s+key\s*\(([^)]*)\)", low)
if c:
pk = parse_columns_list(c.group(1))
continue
c = re.match(r"(?:constraint\s+(\w+)\s+)?unique\s*(?:key\s+\w+\s*)?\(([^)]*)\)", low)
if c:
indexes.append({"name": c.group(1) or f"{name}_unique", "table": name,
"columns": parse_columns_list(c.group(2)), "unique": True, "kind": "unique"})
continue
c = re.match(r"(?:key|index)\s+(\w+)\s*\(([^)]*)\)", low)
if c:
indexes.append({"name": c.group(1), "table": name, "columns": parse_columns_list(c.group(2)),
"unique": False, "kind": "index"})
continue
if re.match(r"(constraint|foreign\s+key|check|exclude)\b", low):
continue
col = re.match(r"([a-z_][\w$]*)\s+", low + " ")
if col:
cols.append(col.group(1))
if re.search(r"\bprimary\s+key\b", low):
pk = [col.group(1)]
elif re.search(r"\bunique\b", low):
indexes.append({"name": f"{name}_{col.group(1)}_key", "table": name,
"columns": [col.group(1)], "unique": True, "kind": "unique"})
tables[name] = {"columns": cols}
if pk:
indexes.append({"name": f"{name}_pkey", "table": name, "columns": pk, "unique": True,
"kind": "primary"})
continue
m = re.match(r"create\s+(unique\s+)?index\s+(?:concurrently\s+)?(?:if\s+not\s+exists\s+)?(\w+)\s+on\s+"
r"([\w.]+)\s*(?:using\s+\w+\s*)?\(([^;]*?)\)\s*(include\s*\(([^)]*)\))?\s*(where\s+.*)?$",
s, re.I | re.S)
if m:
cols = parse_columns_list(m.group(4))
indexes.append({"name": m.group(2), "table": m.group(3).split(".")[-1].lower(), "columns": cols,
"unique": bool(m.group(1)), "kind": "index",
"include": parse_columns_list(m.group(6)) if m.group(6) else [],
"partial": (m.group(7) or "").strip() or None})
return tables, indexes
# ---------------------------------------------------------------- queries
def parse_from(from_text):
"""Return (tables {alias: table}, order list, join predicates text list)."""
aliases, order, ons = {}, [], []
pieces = re.split(r"\b((?:natural\s+)?(?:inner\s+|left\s+(?:outer\s+)?|right\s+(?:outer\s+)?|full\s+(?:outer\s+)?|"
r"cross\s+)?join)\b", from_text, flags=re.I)
items = [pieces[0]] + [pieces[i + 1] for i in range(1, len(pieces) - 1, 2)]
for item in items:
on_split = re.split(r"\bon\b", item, maxsplit=1, flags=re.I)
using = re.search(r"\busing\s*\(([^)]*)\)", on_split[0], re.I)
head = re.sub(r"\busing\s*\([^)]*\)", "", on_split[0], flags=re.I)
for ref in head.split(","):
toks = [t for t in re.split(r"\s+", ref.strip()) if t and t.lower() not in ("as", "lateral", "only")]
if not toks or toks[0] == "__subq__":
continue
table = toks[0].split(".")[-1].lower()
alias = toks[1].lower() if len(toks) > 1 else table
aliases[alias] = table
order.append(alias)
if len(on_split) > 1:
ons.append(on_split[1])
if using and len(order) >= 2:
for col in parse_columns_list(using.group(1)):
ons.append(f"{order[-2]}.{col} = {order[-1]}.{col}")
return aliases, order, ons
COL = r"((?:[a-z_][\w$]*\.)?[a-z_][\w$]*)"
VALUE = r"(?:__lit\d+__|\?|:\w+|\$\d+|@\w+|%s|-?\d+(?:\.\d+)?|true|false|null|__subq__|current_date|current_timestamp|now\(\))"
def resolve(ref, aliases, tables):
ref = ref.lower()
if "." in ref:
a, c = ref.split(".", 1)
return (aliases.get(a, a), c)
if len(set(aliases.values())) == 1:
return (next(iter(aliases.values())), ref)
owners = [t for t in set(aliases.values()) if ref in tables.get(t, {}).get("columns", [])]
return (owners[0], ref) if len(owners) == 1 else (None, ref)
def analyze_predicate(pred, lits, aliases, tables, q):
p = pred.strip()
while p.startswith("(") and p.endswith(")") and len(split_top(p[1:-1], r"\band\b")) >= 1 and \
p.count("(") == p.count(")") and _balanced_wrap(p):
p = p[1:-1].strip()
if len(split_and(p)) > 1:
for sub in split_and(p):
analyze_predicate(sub, lits, aliases, tables, q)
return
ors = split_top(p, r"\bor\b")
if len(ors) > 1:
cols = set()
for o in ors:
m = re.match(rf"^\(?\s*{COL}\s*(=|in\b)", o.strip(), re.I)
cols.add(m.group(1).lower() if m else None)
if len(cols) == 1 and None not in cols:
t, c = resolve(cols.pop(), aliases, tables)
q["filters"].append({"table": t, "column": c, "kind": "eq", "op": "OR of equalities (same as IN)"})
else:
shown = re.sub(r"__lit(\d+)__", lambda m: "'" + lits[int(m.group(1))] + "'", p)
shown = shown if len(shown) <= 70 else shown[:67] + "..."
q["warnings"].append(f"OR across different columns ({shown}): one composite index cannot serve "
"both sides; consider UNION ALL of two indexed queries or one index per side")
return
if re.match(r"^not\b", p, re.I) or re.search(r"(<>|!=|\bnot\s+in\b|\bnot\s+like\b)", p, re.I):
m = re.match(rf"^(?:not\s+)?{COL}", p, re.I)
shown = re.sub(r"__lit(\d+)__", lambda m: "'" + lits[int(m.group(1))] + "'", p)[:50]
q["notes"].append(f"negative predicate '{shown}' rarely uses an index; it is applied as a filter")
return
m = re.match(rf"^{COL}\s*(=|<=>)\s*{COL}$", p, re.I)
if m and not re.fullmatch(VALUE, m.group(3), re.I) and m.group(3).lower() not in KEYWORDS:
left, right = resolve(m.group(1), aliases, tables), resolve(m.group(3), aliases, tables)
if left[0] and right[0] and left[0] != right[0]:
q["joins"].append((left, right))
return
m = re.match(rf"^{VALUE}\s*(=|<|>|<=|>=)\s*{COL}$", p, re.I)
if m:
flip = {"<": ">", ">": "<", "<=": ">=", ">=": "<=", "=": "="}
p = f"{m.group(2)} {flip[m.group(1)]} __v__"
m = re.match(rf"^{COL}\s*(=|<=>)\s*(.+)$", p, re.I)
if m and m.group(1).lower() not in KEYWORDS:
t, c = resolve(m.group(1), aliases, tables)
q["filters"].append({"table": t, "column": c, "kind": "eq", "op": "="})
return
m = re.match(rf"^{COL}\s+in\s+__subq__$", p, re.I)
if m:
t, c = resolve(m.group(1), aliases, tables)
q["filters"].append({"table": t, "column": c, "kind": "eq", "op": "IN (subquery)"})
return
m = re.match(rf"^{COL}\s+in\s*\((.*)\)$", p, re.I | re.S)
if m:
t, c = resolve(m.group(1), aliases, tables)
q["filters"].append({"table": t, "column": c, "kind": "eq", "op": "IN"})
return
m = re.match(rf"^{COL}\s+is\s+(not\s+)?null$", p, re.I)
if m:
t, c = resolve(m.group(1), aliases, tables)
if m.group(2):
q["notes"].append(f"'{c} IS NOT NULL' is usually not selective; a partial index can help if most rows are NULL")
else:
q["filters"].append({"table": t, "column": c, "kind": "eq", "op": "IS NULL"})
return
m = re.match(rf"^{COL}\s*(<|>|<=|>=)\s*(.+)$", p, re.I) or re.match(rf"^{COL}\s+between\s+(.+)\s+and\s+(.+)$", p, re.I)
if m and m.group(1).lower() not in KEYWORDS:
t, c = resolve(m.group(1), aliases, tables)
q["filters"].append({"table": t, "column": c, "kind": "range", "op": "range"})
return
m = re.match(rf"^{COL}\s+(i?like)\s+__lit(\d+)__", p, re.I)
if m:
t, c = resolve(m.group(1), aliases, tables)
pattern = lits[int(m.group(3))]
if pattern.startswith(("%", "_")):
q["warnings"].append(f"non-sargable: {c} {m.group(2).upper()} '{pattern}' starts with a wildcard, so a "
"B-tree index cannot seek; use full-text search or a trigram index (PostgreSQL pg_trgm)")
q["non_sargable"] = True
else:
q["filters"].append({"table": t, "column": c, "kind": "range", "op": f"LIKE '{pattern}'"})
if m.group(2).lower() == "ilike":
q["notes"].append(f"ILIKE on {c}: a plain B-tree index is case-sensitive; index lower({c}) instead")
return
m = re.match(rf"^([a-z_]+)\s*\(\s*{COL}[^)]*\)\s*(=|<|>|<=|>=|like|between)", p, re.I)
if m and m.group(1).lower() not in KEYWORDS:
func, col = m.group(1).lower(), m.group(2)
t, c = resolve(col, aliases, tables)
wild = re.search(r"like\s+__lit(\d+)__", p, re.I)
extra = ""
if wild and lits[int(wild.group(1))].startswith(("%", "_")):
extra = (f"; the LIKE pattern '{lits[int(wild.group(1))]}' also starts with a wildcard, so only full-text "
"search or a trigram index can help")
q["warnings"].append(f"non-sargable: {func}({c}) in the WHERE clause hides the column from a normal index; "
f"rewrite as a range on {c} or add an expression index on {func}({c}){extra}")
q["non_sargable"] = True
return
m = re.match(rf"^{COL}\s*[-+*/]\s*\S+\s*(=|<|>|<=|>=)", p, re.I)
if m:
t, c = resolve(m.group(1), aliases, tables)
q["warnings"].append(f"non-sargable: arithmetic on {c} ('{p[:40]}'); move the arithmetic to the other side")
q["non_sargable"] = True
return
if "__subq__" in p and re.search(r"\bexists\b", p, re.I):
return
q["notes"].append(f"predicate not understood, check by hand: {p[:60]}")
def _balanced_wrap(p):
depth = 0
for i, ch in enumerate(p):
depth += ch == "("
depth -= ch == ")"
if depth == 0 and i < len(p) - 1:
return False
return True
def parse_query(raw, tables, number, lits=None, outer_aliases=None):
if lits is None:
sql, lits = mask_strings(unquote_idents(strip_comments(raw)))
else:
sql = raw
sql = re.sub(r"\s+", " ", sql).strip()
outer, subs = extract_subqueries(sql)
shown = re.sub(r"__lit(\d+)__", lambda m: "'" + lits[int(m.group(1))] + "'", re.sub(r"\s+", " ", raw.strip()))
shown = re.sub(r"\s+", " ", shown)
q = {"n": number, "text": shown[:110] + ("..." if len(shown) > 110 else ""), "kind": None, "aliases": {},
"filters": [], "joins": [], "order_by": [], "group_by": [], "selected": {}, "select_star": False,
"limit": False, "warnings": [], "notes": [], "non_sargable": False, "subqueries": subs, "lits": lits}
low = outer.lower()
cte_names = set()
if low.startswith("with "):
cte_names = {n.lower() for n in re.findall(r"(?:with|,)\s*(?:recursive\s+)?(\w+)\s+as\b", outer, re.I)}
q["notes"].append(f"CTE {', '.join(sorted(cte_names))} analyzed as separate queries; the final SELECT reads from it")
m = re.search(r"(?:\)|__subq__)\s*((?:select|update|delete)\b.*)$", outer, re.I)
outer = m.group(1) if m else outer
low = outer.lower()
if low.startswith("select"):
q["kind"] = "SELECT"
m = re.match(r"select\s+(?:distinct\s+)?(.*?)\s+from\s+(.*?)" + CLAUSE_END, outer, re.I)
if not m:
q["notes"].append("no FROM clause found")
return q
select_list, from_text = m.group(1), m.group(2)
elif low.startswith("update"):
q["kind"] = "UPDATE"
m = re.match(r"update\s+(.*?)\s+set\s+", outer, re.I)
select_list, from_text = "", m.group(1) if m else ""
elif low.startswith("delete"):
q["kind"] = "DELETE"
m = re.match(r"delete\s+from\s+(.*?)" + CLAUSE_END, outer, re.I)
select_list, from_text = "", m.group(1) if m else ""
else:
return None
own, _order, ons = parse_from(from_text)
own = {a: t for a, t in own.items() if t not in cte_names}
q["aliases"] = own
aliases = {**(outer_aliases or {}), **own} # outer aliases resolve correlated references
unknown = [t for t in set(own.values()) if tables and t not in tables]
if unknown:
q["notes"].append(f"table(s) not in the schema: {', '.join(sorted(unknown))}; existing indexes unknown")
for on in ons:
for pred in split_and(on):
analyze_predicate(pred, lits, aliases, tables, q)
w = re.search(r"\bwhere\b(.*?)(?=\b(?:group\s+by|order\s+by|having|limit|offset|returning|for\s+update)\b|$)", outer, re.I)
if w:
for pred in split_and(w.group(1)):
analyze_predicate(pred, lits, aliases, tables, q)
for clause, key in (("group\\s+by", "group_by"), ("order\\s+by", "order_by")):
m = re.search(rf"\b{clause}\b(.*?)(?=\b(?:having|order\s+by|limit|offset|for\s+update)\b|$)", outer, re.I)
if m:
for item in split_top(m.group(1), r","):
mm = re.match(rf"^{COL}\s*(asc|desc)?(?:\s+nulls\s+(?:first|last))?$", item.strip(), re.I)
if mm:
t, c = resolve(mm.group(1), aliases, tables)
q[key].append({"table": t, "column": c, "dir": (mm.group(2) or "asc").lower()})
else:
q["notes"].append(f"{key.replace('_', ' ')} expression '{item.strip()[:40]}' cannot use a plain column index")
q["limit"] = bool(re.search(r"\b(limit|fetch\s+first)\b", outer, re.I))
if select_list:
if re.search(r"(^|,)\s*(\w+\.)?\*\s*(,|$)", select_list):
q["select_star"] = True
for ref in re.findall(rf"\b{COL}\b(?!\s*\()", select_list, re.I):
if ref.lower() in KEYWORDS or ref.startswith("__") or re.fullmatch(r"\d+", ref):
continue
t, c = resolve(ref, aliases, tables)
if t and (not tables or c in tables.get(t, {}).get("columns", [c])):
q["selected"].setdefault(t, [])
if c not in q["selected"][t]:
q["selected"][t].append(c)
for f in q["filters"]:
if f["table"] is None:
q["notes"].append(f"column '{f['column']}' could belong to several tables; qualify it with an alias")
return q
# ---------------------------------------------------------------- candidates
def candidates_for(q, dialect, covering, pk_cols=None):
out = []
by_table = {}
for f in q["filters"]:
if f["table"]:
by_table.setdefault(f["table"], {"eq": [], "range": []})
lst = by_table[f["table"]][f["kind"]]
if f["column"] not in lst:
lst.append(f["column"])
tables_in_q = set(q["aliases"].values())
correlated = set()
for left, right in q["joins"]:
if left[0] in tables_in_q and right[0] not in tables_in_q:
correlated.add(left[0])
if right[0] in tables_in_q and left[0] not in tables_in_q:
correlated.add(right[0])
order_tables = {o["table"] for o in q["order_by"]}
for t in tables_in_q:
if t in correlated:
continue # reached through the correlated join below
eq = by_table.get(t, {}).get("eq", [])
rng = [c for c in by_table.get(t, {}).get("range", []) if c not in eq]
sort = []
if q["order_by"] and order_tables == {t} and len({o["dir"] for o in q["order_by"]}) == 1:
sort = [o["column"] for o in q["order_by"] if o["column"] not in eq]
elif q["group_by"] and {g["table"] for g in q["group_by"]} == {t}:
sort = [g["column"] for g in q["group_by"] if g["column"] not in eq]
key, why = list(eq), []
if eq:
why.append(f"equality on {', '.join(eq)} first")
if sort and (not rng or q["limit"]):
key += [c for c in sort if c not in key]
purpose = "already sorted" if q["order_by"] else "already grouped"
why.append(f"then {', '.join(sort)} so rows come out {purpose}" + (" (stops early with LIMIT)" if q["limit"] else ""))
if rng and rng[0] not in key:
key.append(rng[0])
why.append(f"{rng[0]} last as an in-index filter")
elif rng:
key.append(rng[0])
why.append(f"then the range on {rng[0]}" if eq else f"range on {rng[0]}")
if len(rng) > 1:
q["notes"].append(f"several range filters on {t} ({', '.join(rng)}): only the first can seek; the rest filter")
if sort:
q["notes"].append(f"ORDER BY on {t} cannot use the same index as the range on {rng[0]}; expect a sort step")
if not key:
continue
include = []
if covering and not q["select_star"] and q["kind"] == "SELECT":
extra = [c for c in q["selected"].get(t, []) if c not in key
and not (dialect == "mysql" and c in (pk_cols or {}).get(t, []))]
if 0 < len(extra) <= 3:
include = extra
out.append({"table": t, "columns": key, "include": include, "why": "; ".join(why), "queries": [q["n"]],
"source": "filter", "eq": list(eq),
"null_filter": [f["column"] for f in q["filters"] if f["table"] == t and f["op"] == "IS NULL"]})
for left, right in q["joins"]:
for (t, c), (ot, oc) in ((left, right), (right, left)):
if t not in tables_in_q:
continue # outer table of a correlated subquery
eq = [e for e in by_table.get(t, {}).get("eq", []) if e != c]
rng = [r for r in by_table.get(t, {}).get("range", []) if r != c and r not in eq][:1]
why = f"join column {t}.{c} = {ot}.{oc} first (lets the planner look up matching rows)"
if eq or rng:
why += f", then {', '.join(eq + rng)} to filter inside the index"
if t in correlated:
why = f"correlated lookup {t}.{c} = outer {ot}.{oc} first" + (f", then {', '.join(eq + rng)}" if eq or rng else "")
out.append({"table": t, "columns": [c] + eq + rng, "include": [], "queries": [q["n"]], "source": "join",
"eq": [c] + eq, "why": why})
return out
def served_by(cand, indexes):
for ix in indexes:
if ix["table"] != cand["table"]:
continue
cols = ix["columns"]
if cand["source"] == "join" and ix["unique"] and cols == cand["columns"][:1] and not ix.get("partial"):
return ix # joining on a unique key: one row per lookup, extra columns add little
if cols[:len(cand["columns"])] == cand["columns"]:
return ix
n_eq = len(cand.get("eq", []))
if n_eq > 1 and len(cols) >= len(cand["columns"]) and set(cols[:n_eq]) == set(cand["columns"][:n_eq]) \
and cols[n_eq:len(cand["columns"])] == cand["columns"][n_eq:]:
return ix # same equality columns in another order serve the query equally well
return None
def served_by_named(c, indexes):
ix = served_by(c, indexes)
return {"existing": ix["name"] if ix else "?"}
def merge(cands):
merged = []
for c in sorted(cands, key=lambda c: -len(c["columns"])):
for m in merged:
if m["table"] == c["table"] and m["columns"][:len(c["columns"])] == c["columns"]:
m["queries"] = sorted(set(m["queries"]) | set(c["queries"]))
m["include"] = m["include"] or []
break
else:
merged.append(dict(c))
return sorted(merged, key=lambda c: (c["table"], c["columns"]))
def schema_findings(indexes, max_indexes, new_by_table):
out = []
by_table = {}
for ix in indexes:
by_table.setdefault(ix["table"], []).append(ix)
for t, ixs in by_table.items():
for i, a in enumerate(ixs):
for b in ixs[i + 1:]:
if a["columns"] == b["columns"] and (a.get("partial") == b.get("partial")):
out.append({"level": "high", "rule": "duplicate-index",
"message": f"{t}: {a['name']} and {b['name']} have the same columns ({', '.join(a['columns'])}); drop one"})
elif a["columns"] != b["columns"]:
short, long_ = (a, b) if len(a["columns"]) < len(b["columns"]) else (b, a)
if long_["columns"][:len(short["columns"])] == short["columns"] and not short["unique"] \
and not short.get("partial"):
out.append({"level": "warn", "rule": "redundant-prefix",
"message": f"{t}: {short['name']} ({', '.join(short['columns'])}) is a leftmost prefix of "
f"{long_['name']} ({', '.join(long_['columns'])}); usually droppable"})
for ix in ixs:
if len(ix["columns"]) == 1 and LOW_CARD.search(ix["columns"][0]) and ix["kind"] == "index" and not ix.get("partial"):
out.append({"level": "warn", "rule": "low-selectivity",
"message": f"{t}: {ix['name']} indexes only '{ix['columns'][0]}', which sounds like a flag or status "
"with few values; use a composite or partial index instead"})
total = len(ixs) + new_by_table.get(t, 0)
if total > max_indexes:
out.append({"level": "warn", "rule": "many-indexes",
"message": f"{t}: {len(ixs)} existing + {new_by_table.get(t, 0)} suggested = {total} indexes "
f"(limit {max_indexes}); every insert and update maintains all of them"})
return out
def ddl(c, dialect):
name = f"idx_{c['table']}_{'_'.join(c['columns'])}"[:63]
cols = ", ".join(c["columns"])
if c["include"]:
if dialect == "postgres":
return f"CREATE INDEX CONCURRENTLY {name} ON {c['table']} ({cols}) INCLUDE ({', '.join(c['include'])});"
cols += ", " + ", ".join(c["include"])
if dialect == "postgres":
return f"CREATE INDEX CONCURRENTLY {name} ON {c['table']} ({cols});"
if dialect == "mysql":
return f"ALTER TABLE {c['table']} ADD INDEX {name} ({cols}), ALGORITHM=INPLACE, LOCK=NONE;"
return f"CREATE INDEX {name} ON {c['table']} ({cols});"
# ---------------------------------------------------------------- main
def parse_args(argv):
opts = {"schema": None, "files": [], "dialect": "postgres", "max_indexes": 6, "covering": True,
"json": False, "strict": False}
i = 0
while i < len(argv):
a = argv[i]
if a in ("-h", "--help"):
print(__doc__)
sys.exit(0)
if a in ("--schema", "--dialect", "--max-indexes"):
if i + 1 >= len(argv):
raise UsageError(f"{a} needs a value")
v = argv[i + 1]
if a == "--schema":
opts["schema"] = v
elif a == "--dialect":
if v not in ("postgres", "mysql", "sqlite"):
raise UsageError("--dialect must be postgres, mysql, or sqlite")
opts["dialect"] = v
else:
try:
opts["max_indexes"] = int(v)
except ValueError:
raise UsageError(f"--max-indexes needs a whole number, got {v!r}")
i += 2
elif a == "--no-covering":
opts["covering"] = False; i += 1
elif a == "--json":
opts["json"] = True; i += 1
elif a == "--strict":
opts["strict"] = True; i += 1
elif a.startswith("--"):
raise UsageError(f"unknown option {a}")
else:
opts["files"].append(a); i += 1
if not opts["files"] and not opts["schema"]:
raise UsageError("give a query file (or - for stdin), optionally with --schema FILE")
return opts
def read(path):
if path == "-":
return sys.stdin.read()
with open(path, encoding="utf-8") as f:
return f.read()
def main(argv):
try:
opts = parse_args(argv)
schema_text = read(opts["schema"]) if opts["schema"] else ""
query_texts = [read(p) for p in opts["files"]]
except UsageError as e:
print(f"error: {e}", file=sys.stderr)
return 2
except OSError as e:
print(f"error: cannot read {e.filename}: {e.strerror}", file=sys.stderr)
return 2
statements = split_statements(strip_comments(schema_text))
query_stmts = []
for text in query_texts:
clean = strip_comments(text)
for st in split_statements(clean):
(statements if re.match(r"\s*create\s", st, re.I) else query_stmts).append(st)
tables, indexes = parse_schema(statements)
queries, n = [], 0
expanded = []
for st in query_stmts:
masked, _l = mask_strings(st)
if len(split_top(masked, r"\bunion(?:\s+all)?\b")) > 1: # a real top-level UNION, not one inside a string
expanded.extend(split_top(st, r"\bunion(?:\s+all)?\b")) # each branch is analyzed as its own query
else:
expanded.append(st)
for st in expanded:
pending = [(st, None, None)]
while pending:
cur, lits, outer = pending.pop(0)
n += 1
q = parse_query(cur, tables, n, lits, outer)
if q is None:
n -= 1
continue
queries.append(q)
for sub in q["subqueries"]:
pending.append((sub, q["lits"], {**(outer or {}), **q["aliases"]}))
q["notes"].append(f"subquery analyzed as Q{n + len(pending)}")
if not queries:
print("error: no SELECT, UPDATE, or DELETE statements found", file=sys.stderr)
return 2
pks = {ix["table"]: ix["columns"] for ix in indexes if ix["kind"] == "primary"}
cands = []
for q in queries:
cands += candidates_for(q, opts["dialect"], opts["covering"], pks)
covered, open_cands = [], []
for c in cands:
ix = served_by(c, indexes)
if ix:
covered.append({**c, "existing": ix["name"]})
else:
open_cands.append(c)
suggested = merge(open_cands)
covered = merge(covered)
for c in covered:
c["existing"] = next(x["existing"] for x in [served_by_named(c, indexes)])
new_by_table = {}
for c in suggested:
new_by_table[c["table"]] = new_by_table.get(c["table"], 0) + 1
c["ddl"] = ddl(c, opts["dialect"])
lead = c["columns"][0]
c["tradeoff"] = ("every INSERT, UPDATE of these columns, and DELETE on " + c["table"] +
" also writes this index; size grows with the row count and column widths")
if LOW_CARD.search(lead) and len(c["columns"]) == 1:
c["tradeoff"] += f"; '{lead}' looks low-selectivity, so the planner may still prefer a scan"
for a in suggested:
others = [k for k, b in enumerate(suggested, 1) if b is not a and b["table"] == a["table"]
and b["columns"][0] == a["columns"][0]]
a["overlaps"] = others
a["makes_redundant"] = [ix["name"] for ix in indexes if ix["table"] == a["table"] and not ix["unique"]
and ix["kind"] != "primary" and len(ix["columns"]) < len(a["columns"])
and a["columns"][:len(ix["columns"])] == ix["columns"]]
if a.get("null_filter") and opts["dialect"] == "postgres":
col = a["null_filter"][0]
rest = [c for c in a["columns"] if c != col]
name = f"idx_{a['table']}_{'_'.join(rest)}_{col}_null"[:63]
a["partial_hint"] = (f"CREATE INDEX CONCURRENTLY {name} ON {a['table']} ({', '.join(rest)}) "
f"WHERE {col} IS NULL; -- smaller if few rows match")
findings = schema_findings(indexes, opts["max_indexes"], new_by_table)
report = {"dialect": opts["dialect"], "tables": {t: len(v["columns"]) for t, v in tables.items()},
"existing_indexes": indexes, "queries": [{k: v for k, v in q.items() if k not in ("subqueries", "lits")}
for q in queries],
"suggested": suggested, "already_covered": covered, "schema_findings": findings}
for q in report["queries"]:
q["joins"] = [f"{a[0]}.{a[1]} = {b[0]}.{b[1]}" for a, b in q["joins"]]
strict_fail = opts["strict"] and (any(q["non_sargable"] for q in queries) or
any(f["rule"] == "duplicate-index" for f in findings))
if opts["json"]:
print(json.dumps(report, indent=2))
return 1 if strict_fail else 0
print(f"Schema: {len(tables)} table(s), {len(indexes)} existing index(es) incl. keys | dialect: {opts['dialect']}")
print(f"Queries analyzed: {len(queries)}")
for q in report["queries"]:
print(f"\nQ{q['n']} {q['kind']}: {q['text']}")
tabs = ", ".join(f"{t} {a}" if a != t else t for a, t in q["aliases"].items())
print(f" tables: {tabs or '-'}")
eqs = [f"{f['table'] or '?'}.{f['column']} ({f['op']})" for f in q["filters"] if f["kind"] == "eq"]
rngs = [f"{f['table'] or '?'}.{f['column']} ({f['op']})" for f in q["filters"] if f["kind"] == "range"]
if eqs:
print(f" equality: {', '.join(eqs)}")
if rngs:
print(f" range: {', '.join(rngs)}")
if q["joins"]:
print(f" joins: {', '.join(q['joins'])}")
if q["order_by"]:
print(" order by: " + ", ".join(f"{o['table']}.{o['column']} {o['dir'].upper()}" for o in q["order_by"])
+ (" (LIMIT)" if q["limit"] else ""))
if q["group_by"]:
print(" group by: " + ", ".join(f"{g['table']}.{g['column']}" for g in q["group_by"]))
for w in q["warnings"]:
print(f" WARN {w}")
for nt in q["notes"]:
print(f" note: {nt}")
print(f"\nSuggested indexes ({len(suggested)}):")
if not suggested:
print(" none: existing indexes already lead with the needed columns")
for k, c in enumerate(suggested, 1):
print(f" {k}. {c['ddl']}")
print(f" serves: {', '.join('Q' + str(x) for x in c['queries'])} | why: {c['why']}")
if c["include"]:
print(f" covering: {', '.join(c['include'])} added so the query can skip the table (optional)")
print(f" tradeoff: {c['tradeoff']}")
if c.get("overlaps"):
print(f" overlap: same leading column as #{', #'.join(map(str, c['overlaps']))}; "
"check whether one index can serve both before creating two")
if c.get("makes_redundant"):
print(f" makes redundant: {', '.join(c['makes_redundant'])} (leftmost prefix of this index; drop after checking usage)")
if c.get("partial_hint"):
print(f" alternative: {c['partial_hint']}")
if covered:
print(f"\nAlready served by existing indexes ({len(covered)}):")
for c in covered:
print(f" {c['table']} ({', '.join(c['columns'])}) -> {c['existing']} (Q{', Q'.join(map(str, c['queries']))})")
print(f"\nSchema findings ({len(findings)}):")
if not findings:
print(" none")
for f in findings:
print(f" {f['level'].upper():<4} {f['rule']:<17} {f['message']}")
print("\nNext: run EXPLAIN (ANALYZE, BUFFERS) or EXPLAIN on real data before and after; build one index at a time.")
return 1 if strict_fail else 0
if __name__ == "__main__":
sys.exit(main(sys.argv[1:]))Reusable i18n workflow for coding agents. Verifies locale completeness, hardcoded text, placeholders, pluralization, fallback behavior, formatting, translation consistency, and localization-related UI regressions.
---
name: i18n-change-workflow
description: Reusable i18n workflow for coding agents. Verifies locale completeness, hardcoded text, placeholders, pluralization, fallback behavior, formatting, translation consistency, and localization-related UI regressions.
---
# i18n Change Workflow
Act as the i18n/l10n specialist layer for the active task.
This skill adds localization-specific constraints and verification. It does not replace the repository's normal implementation, audit, Git, or approval workflow. Follow the active workflow's mutation boundary: during implementation or remediation, apply the required i18n changes; during a read-only audit or review, use these criteria without modifying repository state.
## 1. Inspect the existing i18n system first
Before changing localized behavior:
- read applicable `AGENTS.md` and project documentation;
- identify the current i18n library or project-native mechanism;
- identify supported locales, source/default locale, locale resource locations, fallback behavior, and locale-selection/persistence logic;
- inspect nearby existing keys and call sites before choosing new key names or structures;
- identify project-specific rules for translations, formatting, generated resources, or validation.
Prefer the existing project architecture. Do not introduce a new i18n library, resource format, or parallel translation mechanism unless the task requires it and the repository has no suitable existing mechanism.
Do not treat one framework convention as universal. Follow the repository's actual conventions.
## 2. Classify text before localizing it
Determine whether each changed string is actually user-facing.
Typical localization candidates include:
- visible UI labels, buttons, headings, menus, dialogs, empty states, validation messages, and user-visible errors;
- accessibility labels and descriptions;
- notifications and user-facing system messages;
- placeholders, helper text, onboarding copy, and tooltips;
- user-visible content generated from application-owned templates.
Do not automatically localize:
- identifiers, translation keys, API names, URLs, paths, commands, SQL, regexes, or protocol values;
- developer-only logs, diagnostics, stack traces, and test fixture text;
- brand names, product names, codes, or terms that project rules intentionally preserve;
- externally supplied runtime content unless the task explicitly covers it.
When classification is ambiguous and affects product meaning, preserve the current behavior and surface the ambiguity rather than guessing.
## 3. Preserve the project's key and resource model
For new or changed user-facing text:
- use the project's translation mechanism instead of introducing hardcoded display text when localization is expected;
- follow the existing key naming and namespacing convention;
- prefer stable semantic keys over keys derived from full display sentences unless the project intentionally uses source-text keys;
- update every supported locale required by project rules or the current task;
- preserve unrelated locale entries and target-only data unless deletion is explicitly intended;
- do not silently rename or delete existing keys merely for stylistic consistency.
Treat the project's declared source/default locale as canonical only if the repository actually uses that model.
Missing translations must follow the project's established fallback policy. Do not invent a new fallback policy silently.
## 4. Preserve interpolation, pluralization, and message structure
Translation structure is part of the contract.
- Preserve the same required placeholders/arguments across locale variants.
- Do not translate placeholder names, format tokens, markup, or control syntax.
- Use the project's plural/select/ICU mechanism when grammar depends on count, gender, case, or other locale-sensitive variation.
- Avoid assembling sentences from separately translated fragments when word order or grammar can vary by language.
- Avoid string concatenation that assumes English word order or spacing.
- Preserve intentional markup, escaping, and line-break semantics.
If a source message changes its arguments or message structure, verify every affected locale rather than updating only the visible source text.
## 5. Keep locale-sensitive values locale-aware
When the changed UI contains locale-sensitive values, use the project's existing locale-aware formatting facilities for relevant:
- dates and times;
- numbers and percentages;
- currencies;
- units;
- relative time;
- list formatting;
- plural categories.
Do not hardcode separators, decimal conventions, date ordering, currency placement, or English-only plural assumptions when locale-aware behavior is expected.
## 6. Protect locale selection and fallback behavior
When the task touches locale switching, initialization, persistence, or fallback:
- preserve the project's supported-locale list and normalization rules;
- verify default-locale behavior;
- verify persistence if the project stores the user's language choice;
- verify unsupported or missing locales degrade through the intended fallback path;
- avoid mixed-language UI caused by missing keys or stale cached locale data;
- ensure lazy-loaded locale resources are awaited or synchronized correctly when applicable.
Do not change locale-detection precedence without an explicit requirement.
## 7. Translation quality
When generating or editing translations:
- preserve meaning, intent, tone, and product terminology rather than translating mechanically word-for-word;
- use surrounding UI context to resolve ambiguous short labels;
- preserve approved product names, technical terms, and glossary decisions;
- keep placeholders and markup intact;
- avoid adding claims, meaning, politeness level, or functionality not present in the source;
- flag uncertain, culturally sensitive, legal, safety-critical, or brand-sensitive wording for human confirmation instead of pretending certainty.
If the repository contains a glossary, terminology file, translation memory, or established translations, prefer that evidence over a newly generated alternative.
Read `references/i18n-review-checklist.md` when doing a broad locale addition, translation review, or release-oriented localization change.
## 8. Check UI and layout risk
Localized text can change layout even when the translation is correct.
For affected UI, consider when relevant:
- longer labels and multi-line wrapping;
- narrow mobile widths and responsive layouts;
- CJK line breaking and glyph coverage;
- text truncation and ellipsis;
- buttons, tabs, badges, dialogs, tables, and fixed-width containers;
- font fallback;
- accessibility labels;
- right-to-left direction, mirroring, and logical CSS/layout properties when an RTL locale is in scope.
Do not add RTL-specific work when no RTL locale is supported or requested, but do not ignore it when an RTL locale is part of the task.
Use visual or UI verification when the changed text can plausibly affect layout. A successful locale-file check alone does not prove the UI is correct.
## 9. Verify with project-native checks
Use the repository's existing i18n validators, tests, linters, builds, and UI checks first.
Verify the relevant subset of:
- locale-key completeness/parity;
- missing or blank translations;
- placeholder/argument parity;
- plural/select structure;
- fallback behavior;
- locale switching and persistence;
- locale-aware formatting;
- absence of newly introduced hardcoded user-facing strings in the changed scope;
- build/type/lint/test health;
- layout behavior for affected screens.
For plain JSON locale catalogs, `scripts/check_json_locales.py` may be used as an additional deterministic check. It checks duplicate JSON keys, key parity, value types, blank strings, and common brace-style named placeholder/ICU argument parity. Placeholder detection is intentionally narrow and heuristic; confirm reported mismatches against the project's actual message syntax. It is not a semantic translation review and does not replace project-native tooling.
Do not claim repository-wide i18n completeness from a narrow file or static check.
## 10. Completion criteria
An i18n change is complete only when, for the requested scope:
- the intended user-facing strings use the project's localization mechanism;
- required locale resources are updated;
- placeholders and message structure remain compatible;
- relevant formatting/fallback/switching behavior is preserved;
- project-native verification passes, or limitations are explicitly reported;
- plausible layout regressions have been checked when the UI is affected;
- unresolved translation or product-language ambiguity is reported rather than guessed.
Keep the final report concise. State what locale behavior changed, which locales/resources were touched, what validation actually ran, and any remaining translation or UI limitations.
FILE:references/i18n-review-checklist.md
# i18n Review Checklist
Use this reference for broad locale additions, translation review, or release-oriented localization work. Apply only items relevant to the project and requested scope.
## Coverage
- Inventory the user-visible surfaces in scope.
- Confirm every intended translation candidate is represented by the project i18n mechanism.
- Distinguish deliberate source-language preservation from accidental untranslated text.
- Report dynamic/external/non-text surfaces that cannot be verified from repository resources.
## Resource integrity
- Required keys exist in the locales covered by the task.
- No unrelated locale entries were deleted or rewritten.
- Value types match where the resource format requires them to match.
- Empty translations are intentional or reported.
- Generated locale resources are regenerated only through the project-approved command.
## Message contracts
- Named placeholders and ICU/select arguments are preserved.
- Markup, escapes, formatting tokens, and intentional line breaks remain valid.
- Plural/select branches follow the project's library and locale rules.
- Sentences are not built from fragments that assume source-language word order.
## Language quality
- Meaning and user intent match the source.
- Terminology is consistent with existing product language and glossary decisions.
- Short labels are interpreted using screen/action context, not in isolation.
- Tone, formality, capitalization, and punctuation fit the target locale and existing product voice.
- Brand/product names and deliberately preserved terms remain unchanged.
- High-risk ambiguity is surfaced for human confirmation.
## Locale behavior
When applicable, verify:
- default locale;
- explicit locale switching;
- persistence across reload/restart;
- unsupported-locale fallback;
- missing-key fallback;
- lazy-loaded resource behavior;
- date/time/number/currency/unit formatting;
- locale normalization such as `en-US` vs `en` according to project rules.
## UI and accessibility
When affected, check:
- narrow-screen overflow;
- wrapping, truncation, and fixed-height containers;
- buttons/tabs/badges with longer translations;
- CJK line-breaking and font glyphs;
- screen-reader/accessibility labels;
- RTL direction and mirroring only when RTL locales are in scope.
## Evidence and limitations
A passing resource check proves only what it actually checked. It does not by itself prove:
- translation quality;
- runtime locale switching;
- visual correctness;
- complete coverage of inline/dynamic/non-text content;
- correct external/CMS content.
State those limitations explicitly when they matter.
FILE:scripts/check_json_locales.py
#!/usr/bin/env python3
"""Deterministic structural checks for JSON locale catalogs.
Checks:
- duplicate object keys while parsing
- missing/extra leaf paths relative to a source locale
- source/target leaf type mismatches
- blank target strings
- common named placeholder / ICU argument parity
This intentionally does not judge translation quality and is not a general
hardcoded-string scanner.
"""
from __future__ import annotations
import argparse
import json
import re
import sys
from pathlib import Path
from typing import Any, TypeAlias
ARG_RE = re.compile(r"\{\s*([A-Za-z_][A-Za-z0-9_.-]*)\s*(?:[,}])")
PathPart: TypeAlias = str | int
JSONPath: TypeAlias = tuple[PathPart, ...]
class JSONObjectPairs(list):
"""Marker type preserving JSON object pairs so duplicates remain detectable."""
def _object_pairs_hook(pairs: list[tuple[str, Any]]) -> JSONObjectPairs:
return JSONObjectPairs(pairs)
def path_label(path: JSONPath) -> str:
"""Render an unambiguous JSON-style path without conflating dots in keys."""
if not path:
return "$"
pieces: liststr = []
for part in path:
if isinstance(part, int):
pieces.append(f"[{part}]")
else:
pieces.append(f"[{json.dumps(part, ensure_ascii=False)}]")
return "$" + "".join(pieces)
def _normalize_json(value: Any, path: JSONPath = ()) -> Any:
if isinstance(value, JSONObjectPairs):
out: dict[str, Any] = {}
seen: setstr = set()
for key, child in value:
if key in seen:
raise ValueError(f"duplicate key at {path_label(path + (key,))}")
seen.add(key)
out[key] = _normalize_json(child, path + (key,))
return out
if isinstance(value, list):
return [
_normalize_json(child, path + (index,))
for index, child in enumerate(value)
]
return value
def load_json(path: Path) -> Any:
try:
with path.open("r", encoding="utf-8") as f:
raw = json.load(f, object_pairs_hook=_object_pairs_hook)
return _normalize_json(raw)
except (OSError, json.JSONDecodeError, ValueError) as exc:
raise ValueError(f"{path}: {exc}") from exc
def flatten(value: Any, path: tuple[str, ...] = ()) -> dict[tuple[str, ...], Any]:
"""Flatten JSON objects using tuple paths so literal dots in keys stay distinct."""
out: dict[tuple[str, ...], Any] = {}
if isinstance(value, dict):
for key, child in value.items():
out.update(flatten(child, path + (key,)))
else:
outpath = value
return out
def value_kind(value: Any) -> str:
if isinstance(value, bool):
return "boolean"
if value is None:
return "null"
if isinstance(value, str):
return "string"
if isinstance(value, (int, float)):
return "number"
if isinstance(value, list):
return "array"
return type(value).__name__
def arguments(value: Any) -> setstr:
if not isinstance(value, str):
return set()
return set(ARG_RE.findall(value))
def check_pair(source_path: Path, target_path: Path, allow_extra: bool) -> int:
source = flatten(load_json(source_path))
target = flatten(load_json(target_path))
findings: list[tuple[str, str]] = []
source_keys = set(source)
target_keys = set(target)
for key in sorted(source_keys - target_keys):
findings.append(("ERROR", f"missing key: {path_label(key)}"))
if not allow_extra:
for key in sorted(target_keys - source_keys):
findings.append(("WARN", f"extra key: {path_label(key)}"))
for key in sorted(source_keys & target_keys):
src = source[key]
dst = target[key]
label = path_label(key)
src_kind = value_kind(src)
dst_kind = value_kind(dst)
if src_kind != dst_kind:
findings.append(
("ERROR", f"type mismatch at {label}: source={src_kind}, target={dst_kind}")
)
continue
if isinstance(dst, str) and dst.strip() == "":
findings.append(("WARN", f"blank target string: {label}"))
src_args = arguments(src)
dst_args = arguments(dst)
if src_args != dst_args:
missing = sorted(src_args - dst_args)
extra = sorted(dst_args - src_args)
details: liststr = []
if missing:
details.append(f"missing={missing}")
if extra:
details.append(f"extra={extra}")
findings.append(("ERROR", f"argument mismatch at {label}: {', '.join(details)}"))
print(f"SOURCE: {source_path}")
print(f"TARGET: {target_path}")
if not findings:
print("PASS: no structural findings")
return 0
for severity, message in findings:
print(f"{severity}: {message}")
errors = sum(1 for severity, _ in findings if severity == "ERROR")
warnings = sum(1 for severity, _ in findings if severity == "WARN")
print(f"SUMMARY: {errors} error(s), {warnings} warning(s)")
return 1 if errors else 0
def main() -> int:
parser = argparse.ArgumentParser(
description="Check JSON locale catalogs for structural parity."
)
parser.add_argument("source", type=Path, help="source/default locale JSON")
parser.add_argument("targets", nargs="+", type=Path, help="target locale JSON file(s)")
parser.add_argument(
"--allow-extra",
action="store_true",
help="do not warn about target-only keys",
)
args = parser.parse_args()
try:
statuses = [check_pair(args.source, target, args.allow_extra) for target in args.targets]
except ValueError as exc:
print(f"ERROR: {exc}", file=sys.stderr)
return 2
return 1 if any(status != 0 for status in statuses) else 0
if __name__ == "__main__":
raise SystemExit(main())
FILE:README.md
# i18n-change-workflow
Repository-local Agent Skill for safe i18n/l10n changes.
Suggested location:
`.agents/skills/i18n-change-workflow/`
The optional JSON checker is intentionally narrow and deterministic. It detects duplicate JSON keys and structural mismatches, plus heuristic common brace-style placeholder mismatches; it does not translate text or claim semantic/visual completeness.On-Page SEO: Extracted directly from the DOM via chrome.scripting (Cost: $0). DR / PR: Fetched via OpenPageRank free API (Cost: $0). Backlinks: Scraped via Cloudflare Worker proxying free public tools (Cost: $0). Technical SEO: Fetched via Google PageSpeed Insights free API (Cost: $0). Hosting: Chrome Web Store ($5 one-time fee) or load it unpacked in developer mode (Cost: $0).
Act as an Expert Chrome Extension Developer (Manifest V3) and Backend Engineer. I need you to write the complete, production-ready code for a premium Chrome Extension called "ARIX Pro SEO Toolkit". CRITICAL RULES: 1. NO SCRAPING. Use ONLY official, top-tier SEO APIs. 2. Use Manifest V3, Vanilla JavaScript, HTML, and CSS. No React, no build steps. 3. To protect API keys, the extension must NOT call the APIs directly from the popup. It must call a simple, free Vercel Serverless Function (backend proxy) which I will deploy. TECH STACK & DATA SOURCES: 1. Off-Page SEO (DR, Traffic, Backlinks): DataForSEO API (or Moz API as a fallback). 2. Technical SEO / Core Web Vitals: Google PageSpeed Insights API. FILE STRUCTURE REQUIRED: Please provide the complete code for: 1. `manifest.json` (Manifest V3, permissions: activeTab, storage). 2. `popup.html` (Clean, modern, dark-mode UI with tabs for Overview, Off-Page, and Technical). 3. `popup.css` (Premium styling, clean typography, loading states). 4. `popup.js` (Main controller. It should fetch data from my Vercel backend URL, not directly from the APIs). 5. `api/index.js` (The Vercel Serverless function. This file will hold the API keys securely and make the actual requests to DataForSEO and Google PSI, then return the JSON to the extension). SPECIFIC LOGIC REQUIREMENTS: - BACKEND (api/index.js): - Accept a `domain` and `type` (offpage or technical) query parameter. - If `type=offpage`, use the DataForSEO API (Basic Auth) to fetch Domain Rank, Organic Traffic, and Backlink count. (Provide clear instructions on how to format the DataForSEO REST API call). - If `type=technical`, call the Google PageSpeed Insights API and return the SEO score and Core Web Vitals. - Return clean JSON to the frontend. - FRONTEND (popup.js): - Get the current tab's URL. - Show a sleek loading skeleton while waiting for the Vercel backend. - Display the data in clean cards (e.g., "Domain Rating: 45", "Est. Traffic: 10k", "Backlinks: 5.2k"). - Include basic local caching (`chrome.storage.local`) for 24 hours so we don't waste API credits if the user clicks the same site twice. Please output the code for each file clearly labeled. Ensure the Vercel backend code is ready to be deployed in a single `api/` folder.
The instructions are suitable for both new and current projects.
1# Universal Instructions for React / Next.js Projects23> Purpose: General rules for developing various projects with React + TypeScript, Next.js + TypeScript, and Tailwind CSS.4> Usage: Place this file in the root of a new project as `AGENTS.md`, `CLAUDE.md`, or `PROJECT_RULES.md`, or use it as a base instruction set for an AI agent.5> Important: These instructions do not contain product-specific rules. Keep everything related to an individual project in a separate `PROJECT_RULES.md` file.67---89# 1. Core Principle10...+821 more lines
tabs
Objective: Compare product in current tab to items in other tabs
1. **Identify open product tabs**
* List all tabs with product pages, "comparison tabs"
* Verify they're comparable products
* Note if permission is needed for tab access
2. **Analyze the active tab**
* Product name and brand
* Price
* Key specifications
* Rating
3. **Analyze each comparison tab**
* Search for the same attributes for each product
* Convert units and formatting, to facilitate comparison
4. **Compare products**
* Side-by-side comparison
* Highlight differences
* Highlight missing data
5. **Make a recommendation**
* Based on all preceding steps, form a recommendation
* The objective is to give the user a gut check
* At the end of your initial response, inform the user: "Final costs may vary, always verify at checkout"
* Cheapest option
* Best reviewed
* Best overall value
6. **Handling exceptions**
Prioritize excellent content in your response. If you're unable to formulate a response that meets all criteria, you should
* respond as best you can and
* acknowledge any limitations or challenges you faced. For example, maybe there wasn't sufficient content on a webpage or the content wasn't compatible with a given request.
Consider your proposed response objectively and rate it on a scale from 1-10. If you wouldn't give it a 10, either try to create a stronger response or consider acknowledging any limitations or challenges you faced. The score is just for your own purposes; don't share it with the user.
* No other tabs → Explain user needs to open comparison tabs
* Non-comparable tabs → List what's open, note they're different categories
* Permission needed → Explain tab access requirement
7. **Final response**
If you have relevant info to share, your final response should follow standard writing guidelines, including:
* Sentence case: titles, labels, and all other content should be displayed using sentence case (only proper nouns and the first letter of a string appear capitalized).
* Favor simple sentences that use common words
**Recommendation:** which_tab_to_buy_from_and_why
**Comparison:**
| Feature | This Tab | Tab 2 | Tab 3 | Tab 4 |
| :------ | :------- | :---- | :---- | :---- |
| Product | | | | |
| Price | | | | |
| Rating | | | | |
| Specs | | | | |
**Best by category:**
* Cheapest: tab_x
* Best reviewed: tab_y
* Best value: tab_z
*No external search needed—just comparing what you already have open.*
**Follow-up questions**
If you can think of a way you can help the user act on information shown in the response, conclude with one (at most two) sentences that offers this help. Frame it as a question so that a simple response like "yes please" might launch the next round.I NEED THIS FULLY INTEGRATED, IMPLEMENTED, ENFORCED, HARDENED, FUNCTIONAL AND FULLY PRODUCTIONAL. NO SIMULATIONS, NO DEAD BUTTONS OR TABS, NO STUBS, NO PLACEHOLDERS, NO TODOs. I NEED REAL 3D AVATARS TEXTURES FULLY DONE ULTRA REALISTIC. I NEED THIS UPGRADED TO OMNIPOTENT REAL LEVEL ENTERPRISE MR.OPUS. I NEED AN AVATAR FACTORY THAT CAN PRODUCE AT HIGH OUTPUTS PERFECTION.
An assistant that establishes a session goal, utilizes browser context, and confirms user input when uncertain.
Act as a Context-Aware Email Assistant. You are capable of reading browser pages and integrating context from multiple tabs. Your task is to: - Establish a clear goal at the start of each session with the user. - Dynamically gather context from each shared tab or email thread. - Always seek user confirmation when your certainty about the context is below 95%. Rules: - Do not make assumptions about the context. - Provide clear options based on the gathered context. - Use variables like goal, currentTabContent, and userConfirmation to manage session dynamics.
Provides base R programming guidance covering data structures, data wrangling, statistical modeling, visualization, and I/O, using only packages included in a standard R installation
---
name: base-r
description: Provides base R programming guidance covering data structures, data wrangling, statistical modeling, visualization, and I/O, using only packages included in a standard R installation
---
# Base R Programming Skill
A comprehensive reference for base R programming — covering data structures, control flow, functions, I/O, statistical computing, and plotting.
## Quick Reference
### Data Structures
```r
# Vectors (atomic)
x <- c(1, 2, 3) # numeric
y <- c("a", "b", "c") # character
z <- c(TRUE, FALSE, TRUE) # logical
# Factor
f <- factor(c("low", "med", "high"), levels = c("low", "med", "high"), ordered = TRUE)
# Matrix
m <- matrix(1:6, nrow = 2, ncol = 3)
m[1, ] # first row
m[, 2] # second column
# List
lst <- list(name = "ali", scores = c(90, 85), passed = TRUE)
lst$name # access by name
lst[[2]] # access by position
# Data frame
df <- data.frame(
id = 1:3,
name = c("a", "b", "c"),
value = c(10.5, 20.3, 30.1),
stringsAsFactors = FALSE
)
df[df$value > 15, ] # filter rows
df$new_col <- df$value * 2 # add column
```
### Subsetting
```r
# Vectors
x[1:3] # by position
x[c(TRUE, FALSE)] # by logical
x[x > 5] # by condition
x[-1] # exclude first
# Data frames
df[1:5, ] # first 5 rows
df[, c("name", "value")] # select columns
df[df$value > 10, "name"] # filter + select
subset(df, value > 10, select = c(name, value))
# which() for index positions
idx <- which(df$value == max(df$value))
```
### Control Flow
```r
# if/else
if (x > 0) {
"positive"
} else if (x == 0) {
"zero"
} else {
"negative"
}
# ifelse (vectorized)
ifelse(x > 0, "pos", "neg")
# for loop
for (i in seq_along(x)) {
cat(i, x[i], "\n")
}
# while
while (condition) {
# body
if (stop_cond) break
}
# switch
switch(type,
"a" = do_a(),
"b" = do_b(),
stop("Unknown type")
)
```
### Functions
```r
# Define
my_func <- function(x, y = 1, ...) {
result <- x + y
return(result) # or just: result
}
# Anonymous functions
sapply(1:5, function(x) x^2)
# R 4.1+ shorthand:
sapply(1:5, \(x) x^2)
# Useful: do.call for calling with a list of args
do.call(paste, list("a", "b", sep = "-"))
```
### Apply Family
```r
# sapply — simplify result to vector/matrix
sapply(lst, length)
# lapply — always returns list
lapply(lst, function(x) x[1])
# vapply — like sapply but with type safety
vapply(lst, length, integer(1))
# apply — over matrix margins (1=rows, 2=cols)
apply(m, 2, sum)
# tapply — apply by groups
tapply(df$value, df$group, mean)
# mapply — multivariate
mapply(function(x, y) x + y, 1:3, 4:6)
# aggregate — like tapply for data frames
aggregate(value ~ group, data = df, FUN = mean)
```
### String Operations
```r
paste("a", "b", sep = "-") # "a-b"
paste0("x", 1:3) # "x1" "x2" "x3"
sprintf("%.2f%%", 3.14159) # "3.14%"
nchar("hello") # 5
substr("hello", 1, 3) # "hel"
gsub("old", "new", text) # replace all
grep("pattern", x) # indices of matches
grepl("pattern", x) # logical vector
strsplit("a,b,c", ",") # list("a","b","c")
trimws(" hi ") # "hi"
tolower("ABC") # "abc"
```
### Data I/O
```r
# CSV
df <- read.csv("data.csv", stringsAsFactors = FALSE)
write.csv(df, "output.csv", row.names = FALSE)
# Tab-delimited
df <- read.delim("data.tsv")
# General
df <- read.table("data.txt", header = TRUE, sep = "\t")
# RDS (single R object, preserves types)
saveRDS(obj, "data.rds")
obj <- readRDS("data.rds")
# RData (multiple objects)
save(df1, df2, file = "data.RData")
load("data.RData")
# Connections
con <- file("big.csv", "r")
chunk <- readLines(con, n = 100)
close(con)
```
### Base Plotting
```r
# Scatter
plot(x, y, main = "Title", xlab = "X", ylab = "Y",
pch = 19, col = "steelblue", cex = 1.2)
# Line
plot(x, y, type = "l", lwd = 2, col = "red")
lines(x, y2, col = "blue", lty = 2) # add line
# Bar
barplot(table(df$category), main = "Counts",
col = "lightblue", las = 2)
# Histogram
hist(x, breaks = 30, col = "grey80",
main = "Distribution", xlab = "Value")
# Box plot
boxplot(value ~ group, data = df,
col = "lightyellow", main = "By Group")
# Multiple plots
par(mfrow = c(2, 2)) # 2x2 grid
# ... four plots ...
par(mfrow = c(1, 1)) # reset
# Save to file
png("plot.png", width = 800, height = 600)
plot(x, y)
dev.off()
# Add elements
legend("topright", legend = c("A", "B"),
col = c("red", "blue"), lty = 1)
abline(h = 0, lty = 2, col = "grey")
text(x, y, labels = names, pos = 3, cex = 0.8)
```
### Statistics
```r
# Descriptive
mean(x); median(x); sd(x); var(x)
quantile(x, probs = c(0.25, 0.5, 0.75))
summary(df)
cor(x, y)
table(df$category) # frequency table
# Linear model
fit <- lm(y ~ x1 + x2, data = df)
summary(fit)
coef(fit)
predict(fit, newdata = new_df)
confint(fit)
# t-test
t.test(x, y) # two-sample
t.test(x, mu = 0) # one-sample
t.test(before, after, paired = TRUE)
# Chi-square
chisq.test(table(df$a, df$b))
# ANOVA
fit <- aov(value ~ group, data = df)
summary(fit)
TukeyHSD(fit)
# Correlation test
cor.test(x, y, method = "pearson")
```
### Data Manipulation
```r
# Merge (join)
merged <- merge(df1, df2, by = "id") # inner
merged <- merge(df1, df2, by = "id", all = TRUE) # full outer
merged <- merge(df1, df2, by = "id", all.x = TRUE) # left
# Reshape
wide <- reshape(long, direction = "wide",
idvar = "id", timevar = "time", v.names = "value")
long <- reshape(wide, direction = "long",
varying = list(c("v1", "v2")), v.names = "value")
# Sort
df[order(df$value), ] # ascending
df[order(-df$value), ] # descending
df[order(df$group, -df$value), ] # multi-column
# Remove duplicates
df[!duplicated(df), ]
df[!duplicated(df$id), ]
# Stack / combine
rbind(df1, df2) # stack rows (same columns)
cbind(df1, df2) # bind columns (same rows)
# Transform columns
df$log_val <- log(df$value)
df$category <- cut(df$value, breaks = c(0, 10, 20, Inf),
labels = c("low", "med", "high"))
```
### Environment & Debugging
```r
ls() # list objects
rm(x) # remove object
rm(list = ls()) # clear all
str(obj) # structure
class(obj) # class
typeof(obj) # internal type
is.na(x) # check NA
complete.cases(df) # rows without NA
traceback() # after error
debug(my_func) # step through
browser() # breakpoint in code
system.time(expr) # timing
Sys.time() # current time
```
## Reference Files
For deeper coverage, read the reference files in `references/`:
### Function Gotchas & Quick Reference (condensed from R 4.5.3 Reference Manual)
Non-obvious behaviors, surprising defaults, and tricky interactions — only what Claude doesn't already know:
- **data-wrangling.md** — Read when: subsetting returns wrong type, apply on data frame gives unexpected coercion, merge/split/cbind behaves oddly, factor levels persist after filtering, table/duplicated edge cases.
- **modeling.md** — Read when: formula syntax is confusing (`I()`, `*` vs `:`, `/`), aov gives wrong SS type, glm silently fits OLS, nls won't converge, predict returns wrong scale, optim/optimize needs tuning.
- **statistics.md** — Read when: hypothesis test gives surprising result, need to choose correct p.adjust method, clustering parameters seem wrong, distribution function naming is confusing (`d`/`p`/`q`/`r` prefixes).
- **visualization.md** — Read when: par settings reset unexpectedly, layout/mfrow interaction is confusing, axis labels are clipped, colors don't look right, need specialty plots (contour, persp, mosaic, pairs).
- **io-and-text.md** — Read when: read.table silently drops data or misparses columns, regex behaves differently than expected, sprintf formatting is tricky, write.table output has unwanted row names.
- **dates-and-system.md** — Read when: Date/POSIXct conversion gives wrong day, time zones cause off-by-one, difftime units are unexpected, need to find/list/test files programmatically.
- **misc-utilities.md** — Read when: do.call behaves differently than direct call, need Reduce/Filter/Map, tryCatch handler doesn't fire, all.equal returns string not logical, time series functions need setup.
## Tips for Writing Good R Code
- Use `vapply()` over `sapply()` in production code — it enforces return types
- Prefer `seq_along(x)` over `1:length(x)` — the latter breaks when `x` is empty
- Use `stringsAsFactors = FALSE` in `read.csv()` / `data.frame()` (default changed in R 4.0)
- Vectorize operations instead of writing loops when possible
- Use `stop()`, `warning()`, `message()` for error handling — not `print()`
- `<<-` assigns to parent environment — use sparingly and intentionally
- `with(df, expr)` avoids repeating `df$` everywhere
- `Sys.setenv()` and `.Renviron` for environment variables
FILE:references/misc-utilities.md
# Miscellaneous Utilities — Quick Reference
> Non-obvious behaviors, gotchas, and tricky defaults for R functions.
> Only what Claude doesn't already know.
---
## do.call
- `do.call(fun, args_list)` — `args` must be a **list**, even for a single argument.
- `quote = TRUE` prevents evaluation of arguments before the call — needed when passing expressions/symbols.
- Behavior of `substitute` inside `do.call` differs from direct calls. Semantics are not fully defined for this case.
- Useful pattern: `do.call(rbind, list_of_dfs)` to combine a list of data frames.
---
## Reduce / Filter / Map / Find / Position
R's functional programming helpers from base — genuinely non-obvious.
- `Reduce(f, x)` applies binary function `f` cumulatively: `Reduce("+", 1:4)` = `((1+2)+3)+4`. Direction matters for non-commutative ops.
- `Reduce(f, x, accumulate = TRUE)` returns all intermediate results — equivalent to Python's `itertools.accumulate`.
- `Reduce(f, x, right = TRUE)` folds from the right: `f(x1, f(x2, f(x3, x4)))`.
- `Reduce` with `init` adds a starting value: `Reduce(f, x, init = v)` = `f(f(f(v, x1), x2), x3)`.
- `Filter(f, x)` keeps elements where `f(elem)` is `TRUE`. Unlike `x[sapply(x, f)]`, handles `NULL`/empty correctly.
- `Map(f, ...)` is a simple wrapper for `mapply(f, ..., SIMPLIFY = FALSE)` — always returns a list.
- `Find(f, x)` returns the **first** element where `f(elem)` is `TRUE`. `Find(f, x, right = TRUE)` for last.
- `Position(f, x)` returns the **index** of the first match (like `Find` but returns position, not value).
---
## lengths
- `lengths(x)` returns the length of **each element** of a list. Equivalent to `sapply(x, length)` but faster (implemented in C).
- Works on any list-like object. Returns integer vector.
---
## conditions (tryCatch / withCallingHandlers)
- `tryCatch` **unwinds** the call stack — handler runs in the calling environment, not where the error occurred. Cannot resume execution.
- `withCallingHandlers` does NOT unwind — handler runs where the condition was signaled. Can inspect/log then let the condition propagate.
- `tryCatch(expr, error = function(e) e)` returns the error condition object.
- `tryCatch(expr, warning = function(w) {...})` catches the **first** warning and exits. Use `withCallingHandlers` + `invokeRestart("muffleWarning")` to suppress warnings but continue.
- `tryCatch` `finally` clause always runs (like Java try/finally).
- `globalCallingHandlers()` registers handlers that persist for the session (useful for logging).
- Custom conditions: `stop(errorCondition("msg", class = "myError"))` then catch with `tryCatch(..., myError = function(e) ...)`.
---
## all.equal
- Tests **near equality** with tolerance (default `1.5e-8`, i.e., `sqrt(.Machine$double.eps)`).
- Returns `TRUE` or a **character string** describing the difference — NOT `FALSE`. Use `isTRUE(all.equal(x, y))` in conditionals.
- `tolerance` argument controls numeric tolerance. `scale` for absolute vs relative comparison.
- Checks attributes, names, dimensions — more thorough than `==`.
---
## combn
- `combn(n, m)` or `combn(x, m)`: generates all combinations of `m` items from `x`.
- Returns a **matrix** with `m` rows; each column is one combination.
- `FUN` argument applies a function to each combination: `combn(5, 3, sum)` returns sums of all 3-element subsets.
- `simplify = FALSE` returns a list instead of a matrix.
---
## modifyList
- `modifyList(x, val)` replaces elements of list `x` with those in `val` by **name**.
- Setting a value to `NULL` **removes** that element from the list.
- **Does** add new names not in `x` — it uses `x[names(val)] <- val` internally, so any name in `val` gets added or replaced.
---
## relist
- Inverse of `unlist`: given a flat vector and a skeleton list, reconstructs the nested structure.
- `relist(flesh, skeleton)` — `flesh` is the flat data, `skeleton` provides the shape.
- Works with factors, matrices, and nested lists.
---
## txtProgressBar
- `txtProgressBar(min, max, style = 3)` — style 3 shows percentage + bar (most useful).
- Update with `setTxtProgressBar(pb, value)`. Close with `close(pb)`.
- Style 1: rotating `|/-\`, style 2: simple progress. Only style 3 shows percentage.
---
## object.size
- Returns an **estimate** of memory used by an object. Not always exact for shared references.
- `format(object.size(x), units = "MB")` for human-readable output.
- Does not count the size of environments or external pointers.
---
## installed.packages / update.packages
- `installed.packages()` can be slow (scans all packages). Use `find.package()` or `requireNamespace()` to check for a specific package.
- `update.packages(ask = FALSE)` updates all packages without prompting.
- `lib.loc` specifies which library to check/update.
---
## vignette / demo
- `vignette()` lists all vignettes; `vignette("name", package = "pkg")` opens a specific one.
- `demo()` lists all demos; `demo("topic")` runs one interactively.
- `browseVignettes()` opens vignette browser in HTML.
---
## Time series: acf / arima / ts / stl / decompose
- `ts(data, start, frequency)`: `frequency` is observations per unit time (12 for monthly, 4 for quarterly).
- `acf` default `type = "correlation"`. Use `type = "partial"` for PACF. `plot = FALSE` to suppress auto-plotting.
- `arima(x, order = c(p,d,q))` for ARIMA models. `seasonal = list(order = c(P,D,Q), period = S)` for seasonal component.
- `arima` handles `NA` values in the time series (via Kalman filter).
- `stl` requires `s.window` (seasonal window) — must be specified, no default. `s.window = "periodic"` assumes fixed seasonality.
- `decompose`: simpler than `stl`, uses moving averages. `type = "additive"` or `"multiplicative"`.
- `stl` result components: `$time.series` matrix with columns `seasonal`, `trend`, `remainder`.
FILE:references/data-wrangling.md
# Data Wrangling — Quick Reference
> Non-obvious behaviors, gotchas, and tricky defaults for R functions.
> Only what Claude doesn't already know.
---
## Extract / Extract.data.frame
Indexing pitfalls in base R.
- `m[j = 2, i = 1]` is `m[2, 1]` not `m[1, 2]` — argument names are **ignored** in `[`, positional matching only. Never name index args.
- Factor indexing: `x[f]` uses integer codes of factor `f`, not its character labels. Use `x[as.character(f)]` for label-based indexing.
- `x[[]]` with no index is always an error. `x$name` does partial matching by default; `x[["name"]]` does not (exact by default).
- Assigning `NULL` via `x[[i]] <- NULL` or `x$name <- NULL` **deletes** that list element.
- Data frame `[` with single column: `df[, 1]` returns a **vector** (drop=TRUE default for columns), but `df[1, ]` returns a **data frame** (drop=FALSE for rows). Use `drop = FALSE` explicitly.
- Matrix indexing a data frame (`df[cbind(i,j)]`) coerces to matrix first — avoid.
---
## subset
Use interactively only; unsafe for programming.
- `subset` argument uses **non-standard evaluation** — column names are resolved in the data frame, which can silently pick up wrong variables in programmatic use. Use `[` with explicit logic in functions.
- `NA`s in the logical condition are treated as `FALSE` (rows silently dropped).
- Factors may retain unused levels after subsetting; call `droplevels()`.
---
## match / %in%
- `%in%` **never returns NA** — this makes it safe for `if()` conditions unlike `==`.
- `match()` returns position of **first** match only; duplicates in `table` are ignored.
- Factors, raw vectors, and lists are all converted to character before matching.
- `NaN` matches `NaN` but not `NA`; `NA` matches `NA` only.
---
## apply
- On a **data frame**, `apply` coerces to matrix via `as.matrix` first — mixed types become character.
- Return value orientation is transposed: if FUN returns length-n vector, result has dim `c(n, dim(X)[MARGIN])`. Row results become **columns**.
- Factor results are coerced to character in the output array.
- `...` args cannot share names with `X`, `MARGIN`, or `FUN` (partial matching risk).
---
## lapply / sapply / vapply
- `sapply` can return a vector, matrix, or list unpredictably — use `vapply` in non-interactive code with explicit `FUN.VALUE` template.
- Calling primitives directly in `lapply` can cause dispatch issues; wrap in `function(x) is.numeric(x)` rather than bare `is.numeric`.
- `sapply` with `simplify = "array"` can produce higher-rank arrays (not just matrices).
---
## tapply
- Returns an **array** (not a data frame). Class info on return values is **discarded** (e.g., Date objects become numeric).
- `...` args to FUN are **not** divided into cells — they apply globally, so FUN should not expect additional args with same length as X.
- `default = NA` fills empty cells; set `default = 0` for sum-like operations. Before R 3.4.0 this was hard-coded to `NA`.
- Use `array2DF()` to convert result to a data frame.
---
## mapply
- Argument name is `SIMPLIFY` (all caps) not `simplify` — inconsistent with `sapply`.
- `MoreArgs` must be a **list** of args not vectorized over.
- Recycles shorter args to common length; zero-length arg gives zero-length result.
---
## merge
- Default `by` is `intersect(names(x), names(y))` — can silently merge on unintended columns if data frames share column names.
- `by = 0` or `by = "row.names"` merges on row names, adding a "Row.names" column.
- `by = NULL` (or both `by.x`/`by.y` length 0) produces **Cartesian product**.
- Result is sorted on `by` columns by default (`sort = TRUE`). For unsorted output use `sort = FALSE`.
- Duplicate key matches produce **all combinations** (one row per match pair).
---
## split
- If `f` is a list of factors, interaction is used; levels containing `"."` can cause unexpected splits unless `sep` is changed.
- `drop = FALSE` (default) retains empty factor levels as empty list elements.
- Supports formula syntax: `split(df, ~ Month)`.
---
## cbind / rbind
- `cbind` on data frames calls `data.frame(...)`, not `cbind.matrix`. Mixing matrices and data frames can give unexpected results.
- `rbind` on data frames matches columns **by name**, not position. Missing columns get `NA`.
- `cbind(NULL)` returns `NULL` (not a matrix). For consistency, `rbind(NULL)` also returns `NULL`.
---
## table
- By default **excludes NA** (`useNA = "no"`). Use `useNA = "ifany"` or `exclude = NULL` to count NAs.
- Setting `exclude` non-empty and non-default implies `useNA = "ifany"`.
- Result is always an **array** (even 1D), class "table". Convert to data frame with `as.data.frame(tbl)`.
- Two kinds of NA (factor-level NA vs actual NA) are treated differently depending on `useNA`/`exclude`.
---
## duplicated / unique
- `duplicated` marks the **second and later** occurrences as TRUE, not the first. Use `fromLast = TRUE` to reverse.
- For data frames, operates on whole rows. For lists, compares recursively.
- `unique` keeps the **first** occurrence of each value.
---
## data.frame (gotchas)
- `stringsAsFactors = FALSE` is the default since R 4.0.0 (was TRUE before).
- Atomic vectors recycle to match longest column, but only if exact multiple. Protect with `I()` to prevent conversion.
- Duplicate column names allowed only with `check.names = FALSE`, but many operations will de-dup them silently.
- Matrix arguments are expanded to multiple columns unless protected by `I()`.
---
## factor (gotchas)
- `as.numeric(f)` returns **integer codes**, not original values. Use `as.numeric(levels(f))[f]` or `as.numeric(as.character(f))`.
- Only `==` and `!=` work between factors; factors must have identical level sets. Ordered factors support `<`, `>`.
- `c()` on factors unions level sets (since R 4.1.0), but earlier versions converted to integer.
- Levels are sorted by default, but sort order is **locale-dependent** at creation time.
---
## aggregate
- Formula interface (`aggregate(y ~ x, data, FUN)`) drops `NA` groups by default.
- The data frame method requires `by` as a **list** (not a vector).
- Returns columns named after the grouping variables, with result column keeping the original name.
- If FUN returns multiple values, result column is a **matrix column** inside the data frame.
---
## complete.cases
- Returns a logical vector: TRUE for rows with **no** NAs across all columns/arguments.
- Works on multiple arguments (e.g., `complete.cases(x, y)` checks both).
---
## order
- Returns a **permutation vector** of indices, not the sorted values. Use `x[order(x)]` to sort.
- Default is ascending; use `-x` for descending numeric, or `decreasing = TRUE`.
- For character sorting, depends on locale. Use `method = "radix"` for locale-independent fast sorting.
- `sort.int()` with `method = "radix"` is much faster for large integer/character vectors.
FILE:references/dates-and-system.md
# Dates and System — Quick Reference
> Non-obvious behaviors, gotchas, and tricky defaults for R functions.
> Only what Claude doesn't already know.
---
## Dates (Date class)
- `Date` objects are stored as **integer days since 1970-01-01**. Arithmetic works in days.
- `Sys.Date()` returns current date as Date object.
- `seq.Date(from, to, by = "month")` — "month" increments can produce varying-length intervals. Adding 1 month to Jan 31 gives Mar 3 (not Feb 28).
- `diff(dates)` returns a `difftime` object in days.
- `format(date, "%Y")` for year, `"%m"` for month, `"%d"` for day, `"%A"` for weekday name (locale-dependent).
- Years before 1CE may not be handled correctly.
- `length(date_vector) <- n` pads with `NA`s if extended.
---
## DateTimeClasses (POSIXct / POSIXlt)
- `POSIXct`: seconds since 1970-01-01 UTC (compact, a numeric vector).
- `POSIXlt`: list with components `$sec`, `$min`, `$hour`, `$mday`, `$mon` (0-11!), `$year` (since 1900!), `$wday` (0-6, Sunday=0), `$yday` (0-365).
- Converting between POSIXct and Date: `as.Date(posixct_obj)` uses `tz = "UTC"` by default — may give different date than intended if original was in another timezone.
- `Sys.time()` returns POSIXct in current timezone.
- `strptime` returns POSIXlt; `as.POSIXct(strptime(...))` to get POSIXct.
- `difftime` arithmetic: subtracting POSIXct objects gives difftime. Units auto-selected ("secs", "mins", "hours", "days", "weeks").
---
## difftime
- `difftime(time1, time2, units = "auto")` — auto-selects smallest sensible unit.
- Explicit units: `"secs"`, `"mins"`, `"hours"`, `"days"`, `"weeks"`. No "months" or "years" (variable length).
- `as.numeric(diff, units = "hours")` to extract numeric value in specific units.
- `units(diff_obj) <- "hours"` changes the unit in place.
---
## system.time / proc.time
- `system.time(expr)` returns `user`, `system`, and `elapsed` time.
- `gcFirst = TRUE` (default): runs garbage collection before timing for more consistent results.
- `proc.time()` returns cumulative time since R started — take differences for intervals.
- `elapsed` (wall clock) can be less than `user` (multi-threaded BLAS) or more (I/O waits).
---
## Sys.sleep
- `Sys.sleep(seconds)` — allows fractional seconds. Actual sleep may be longer (OS scheduling).
- The process **yields** to the OS during sleep (does not busy-wait).
---
## options (key options)
Selected non-obvious options:
- `options(scipen = n)`: positive biases toward fixed notation, negative toward scientific. Default 0. Applies to `print`/`format`/`cat` but not `sprintf`.
- `options(digits = n)`: significant digits for printing (1-22, default 7). Suggestion only.
- `options(digits.secs = n)`: max decimal digits for seconds in time formatting (0-6, default 0).
- `options(warn = n)`: -1 = ignore warnings, 0 = collect (default), 1 = immediate, 2 = convert to errors.
- `options(error = recover)`: drop into debugger on error. `options(error = NULL)` resets to default.
- `options(OutDec = ",")`: change decimal separator in output (affects `format`, `print`, NOT `sprintf`).
- `options(stringsAsFactors = FALSE)`: global default for `data.frame` (moot since R 4.0.0 where it's already FALSE).
- `options(expressions = 5000)`: max nested evaluations. Increase for deep recursion.
- `options(max.print = 99999)`: controls truncation in `print` output.
- `options(na.action = "na.omit")`: default NA handling in model functions.
- `options(contrasts = c("contr.treatment", "contr.poly"))`: default contrasts for unordered/ordered factors.
---
## file.path / basename / dirname
- `file.path("a", "b", "c.txt")` → `"a/b/c.txt"` (platform-appropriate separator).
- `basename("/a/b/c.txt")` → `"c.txt"`. `dirname("/a/b/c.txt")` → `"/a/b"`.
- `file.path` does NOT normalize paths (no `..` resolution); use `normalizePath()` for that.
---
## list.files
- `list.files(pattern = "*.csv")` — `pattern` is a **regex**, not a glob! Use `glob2rx("*.csv")` or `"\\.csv$"`.
- `full.names = FALSE` (default) returns basenames only. Use `full.names = TRUE` for complete paths.
- `recursive = TRUE` to search subdirectories.
- `all.files = TRUE` to include hidden files (starting with `.`).
---
## file.info
- Returns data frame with `size`, `isdir`, `mode`, `mtime`, `ctime`, `atime`, `uid`, `gid`.
- `mtime`: modification time (POSIXct). Useful for `file.info(f)$mtime`.
- On some filesystems, `ctime` is status-change time, not creation time.
---
## file_test
- `file_test("-f", path)`: TRUE if regular file exists.
- `file_test("-d", path)`: TRUE if directory exists.
- `file_test("-nt", f1, f2)`: TRUE if f1 is newer than f2.
- More reliable than `file.exists()` for distinguishing files from directories.
FILE:references/io-and-text.md
# I/O and Text Processing — Quick Reference
> Non-obvious behaviors, gotchas, and tricky defaults for R functions.
> Only what Claude doesn't already know.
---
## read.table (gotchas)
- `sep = ""` (default) means **any whitespace** (spaces, tabs, newlines) — not a literal empty string.
- `comment.char = "#"` by default — lines with `#` are truncated. Use `comment.char = ""` to disable (also faster).
- `header` auto-detection: set to TRUE if first row has **one fewer field** than subsequent rows (the missing field is assumed to be row names).
- `colClasses = "NULL"` **skips** that column entirely — very useful for speed.
- `read.csv` defaults differ from `read.table`: `header = TRUE`, `sep = ","`, `fill = TRUE`, `comment.char = ""`.
- For large files: specifying `colClasses` and `nrows` dramatically reduces memory usage. `read.table` is slow for wide data frames (hundreds of columns); use `scan` or `data.table::fread` for matrices.
- `stringsAsFactors = FALSE` since R 4.0.0 (was TRUE before).
---
## write.table (gotchas)
- `row.names = TRUE` by default — produces an unnamed first column that confuses re-reading. Use `row.names = FALSE` or `col.names = NA` for Excel-compatible CSV.
- `write.csv` fixes `sep = ","`, `dec = "."`, and uses `qmethod = "double"` — cannot override these via `...`.
- `quote = TRUE` (default) quotes character/factor columns. Numeric columns are never quoted.
- Matrix-like columns in data frames expand to multiple columns silently.
- Slow for data frames with many columns (hundreds+); each column processed separately by class.
---
## read.fwf
- Reads fixed-width format files. `widths` is a vector of field widths.
- **Negative widths skip** that many characters (useful for ignoring fields).
- `buffersize` controls how many lines are read at a time; increase for large files.
- Uses `read.table` internally after splitting fields.
---
## count.fields
- Counts fields per line in a file — useful for diagnosing read errors.
- `sep` and `quote` arguments match those of `read.table`.
---
## grep / grepl / sub / gsub (gotchas)
- Three regex modes: POSIX extended (default), `perl = TRUE`, `fixed = TRUE`. They behave differently for edge cases.
- **Name arguments explicitly** — unnamed args after `x`/`pattern` are matched positionally to `ignore.case`, `perl`, etc. Common source of silent bugs.
- `sub` replaces **first** match only; `gsub` replaces **all** matches.
- Backreferences: `"\\1"` in replacement (double backslash in R strings). With `perl = TRUE`: `"\\U\\1"` for uppercase conversion.
- `grep(value = TRUE)` returns matching **elements**; `grep(value = FALSE)` (default) returns **indices**.
- `grepl` returns logical vector — preferred for filtering.
- `regexpr` returns first match position + length (as attributes); `gregexpr` returns all matches as a list.
- `regexec` returns match + capture group positions; `gregexec` does this for all matches.
- Character classes like `[:alpha:]` must be inside `[[:alpha:]]` (double brackets) in POSIX mode.
---
## strsplit
- Returns a **list** (one element per input string), even for a single string.
- `split = ""` or `split = character(0)` splits into individual characters.
- Match at beginning of string: first element of result is `""`. Match at end: no trailing `""`.
- `fixed = TRUE` is faster and avoids regex interpretation.
- Common mistake: unnamed arguments silently match `fixed`, `perl`, etc.
---
## substr / substring
- `substr(x, start, stop)`: extracts/replaces substring. 1-indexed, inclusive on both ends.
- `substring(x, first, last)`: same but `last` defaults to `1000000L` (effectively "to end"). Vectorized over `first`/`last`.
- Assignment form: `substr(x, 1, 3) <- "abc"` replaces in place (must be same length replacement).
---
## trimws
- `which = "both"` (default), `"left"`, or `"right"`.
- `whitespace = "[ \\t\\r\\n]"` — customizable regex for what counts as whitespace.
---
## nchar
- `type = "bytes"` counts bytes; `type = "chars"` (default) counts characters; `type = "width"` counts display width.
- `nchar(NA)` returns `NA` (not 2). `nchar(factor)` works on the level labels.
- `keepNA = TRUE` (default since R 3.3.0); set to `FALSE` to count `"NA"` as 2 characters.
---
## format / formatC
- `format(x, digits, nsmall)`: `nsmall` forces minimum decimal places. `big.mark = ","` adds thousands separator.
- `formatC(x, format = "f", digits = 2)`: C-style formatting. `format = "e"` for scientific, `"g"` for general.
- `format` returns character vector; always right-justified by default (`justify = "right"`).
---
## type.convert
- Converts character vectors to appropriate types (logical, integer, double, complex, character).
- `as.is = TRUE` (recommended): keeps characters as character, not factor.
- Applied column-wise on data frames. `tryLogical = TRUE` (R 4.3+) converts "TRUE"/"FALSE" columns.
---
## Rscript
- `commandArgs(trailingOnly = TRUE)` gets script arguments (excluding R/Rscript flags).
- `#!` line on Unix: `/usr/bin/env Rscript` or full path.
- `--vanilla` or `--no-init-file` to skip `.Rprofile` loading.
- Exit code: `quit(status = 1)` for error exit.
---
## capture.output
- Captures output from `cat`, `print`, or any expression that writes to stdout.
- `file = NULL` (default) returns character vector. `file = "out.txt"` writes directly to file.
- `type = "message"` captures stderr instead.
---
## URLencode / URLdecode
- `URLencode(url, reserved = FALSE)` by default does NOT encode reserved chars (`/`, `?`, `&`, etc.).
- Set `reserved = TRUE` to encode a URL **component** (query parameter value).
---
## glob2rx
- Converts shell glob patterns to regex: `glob2rx("*.csv")` → `"^.*\\.csv$"`.
- Useful with `list.files(pattern = glob2rx("data_*.RDS"))`.
FILE:references/modeling.md
# Modeling — Quick Reference
> Non-obvious behaviors, gotchas, and tricky defaults for R functions.
> Only what Claude doesn't already know.
---
## formula
Symbolic model specification gotchas.
- `I()` is required to use arithmetic operators literally: `y ~ x + I(x^2)`. Without `I()`, `^` means interaction crossing.
- `*` = main effects + interaction: `a*b` expands to `a + b + a:b`.
- `(a+b+c)^2` = all main effects + all 2-way interactions (not squaring).
- `-` removes terms: `(a+b+c)^2 - a:b` drops only the `a:b` interaction.
- `/` means nesting: `a/b` = `a + b %in% a` = `a + a:b`.
- `.` in formula means "all other columns in data" (in `terms.formula` context) or "previous contents" (in `update.formula`).
- Formula objects carry an **environment** used for variable lookup; `as.formula("y ~ x")` uses `parent.frame()`.
---
## terms / model.matrix
- `model.matrix` creates the design matrix including dummy coding. Default contrasts: `contr.treatment` for unordered factors, `contr.poly` for ordered.
- `terms` object attributes: `order` (interaction order per term), `intercept`, `factors` matrix.
- Column names from `model.matrix` can be surprising: e.g., `factorLevelName` concatenation.
---
## glm
- Default `family = gaussian(link = "identity")` — `glm()` with no `family` silently fits OLS (same as `lm`, but slower and with deviance-based output).
- Common families: `binomial(link = "logit")`, `poisson(link = "log")`, `Gamma(link = "inverse")`, `inverse.gaussian()`.
- `binomial` accepts response as: 0/1 vector, logical, factor (second level = success), or 2-column matrix `cbind(success, failure)`.
- `weights` in `glm` means **prior weights** (not frequency weights) — for frequency weights, use the cbind trick or offset.
- `predict.glm(type = "response")` for predicted probabilities; default `type = "link"` returns log-odds (for logistic) or log-rate (for Poisson).
- `anova(glm_obj, test = "Chisq")` for deviance-based tests; `"F"` is invalid for non-Gaussian families.
- Quasi-families (`quasibinomial`, `quasipoisson`) allow overdispersion — no AIC is computed.
- Convergence: `control = glm.control(maxit = 100)` if default 25 iterations isn't enough.
---
## aov
- `aov` is a wrapper around `lm` that stores extra info for balanced ANOVA. For unbalanced designs, Type I SS (sequential) are computed — order of terms matters.
- For Type III SS, use `car::Anova()` or set contrasts to `contr.sum`/`contr.helmert`.
- Error strata for repeated measures: `aov(y ~ A*B + Error(Subject/B))`.
- `summary.aov` gives ANOVA table; `summary.lm(aov_obj)` gives regression-style summary.
---
## nls
- Requires **good starting values** in `start = list(...)` or convergence fails.
- Self-starting models (`SSlogis`, `SSasymp`, etc.) auto-compute starting values.
- Algorithm `"port"` allows bounds on parameters (`lower`/`upper`).
- If data fits too exactly (no residual noise), convergence check fails — use `control = list(scaleOffset = 1)` or jitter data.
- `weights` argument for weighted NLS; `na.action` for missing value handling.
---
## step / add1
- `step` does **stepwise** model selection by AIC (default). Use `k = log(n)` for BIC.
- Direction: `direction = "both"` (default), `"forward"`, or `"backward"`.
- `add1`/`drop1` evaluate single-term additions/deletions; `step` calls these iteratively.
- `scope` argument defines the upper/lower model bounds for search.
- `step` modifies the model object in place — can be slow for large models with many candidate terms.
---
## predict.lm / predict.glm
- `predict.lm` with `interval = "confidence"` gives CI for **mean** response; `interval = "prediction"` gives PI for **new observation** (wider).
- `newdata` must have columns matching the original formula variables — factors must have the same levels.
- `predict.glm` with `type = "response"` gives predictions on the response scale (e.g., probabilities for logistic); `type = "link"` (default) gives on the link scale.
- `se.fit = TRUE` returns standard errors; for `predict.glm` these are on the **link** scale regardless of `type`.
- `predict.lm` with `type = "terms"` returns the contribution of each term.
---
## loess
- `span` controls smoothness (default 0.75). Span < 1 uses that proportion of points; span > 1 uses all points with adjusted distance.
- Maximum **4 predictors**. Memory usage is roughly **quadratic** in n (1000 points ~ 10MB).
- `degree = 0` (local constant) is allowed but poorly tested — use with caution.
- Not identical to S's `loess`; conditioning is not implemented.
- `normalize = TRUE` (default) standardizes predictors to common scale; set `FALSE` for spatial coords.
---
## lowess vs loess
- `lowess` is the older function; returns `list(x, y)` — cannot predict at new points.
- `loess` is the newer formula interface with `predict` method.
- `lowess` parameter is `f` (span, default 2/3); `loess` parameter is `span` (default 0.75).
- `lowess` `iter` default is 3 (robustifying iterations); `loess` default `family = "gaussian"` (no robustness).
---
## smooth.spline
- Default smoothing parameter selected by **GCV** (generalized cross-validation).
- `cv = TRUE` uses ordinary leave-one-out CV instead — do not use with duplicate x values.
- `spar` and `lambda` control smoothness; `df` can specify equivalent degrees of freedom.
- Returns object with `predict`, `print`, `plot` methods. The `fit` component has knots and coefficients.
---
## optim
- **Minimizes** by default. To maximize: set `control = list(fnscale = -1)`.
- Default method is Nelder-Mead (no gradients, robust but slow). Poor for 1D — use `"Brent"` or `optimize()`.
- `"L-BFGS-B"` is the only method supporting box constraints (`lower`/`upper`). Bounds auto-select this method with a warning.
- `"SANN"` (simulated annealing): convergence code is **always 0** — it never "fails". `maxit` = total function evals (default 10000), no other stopping criterion.
- `parscale`: scale parameters so unit change in each produces comparable objective change. Critical for mixed-scale problems.
- `hessian = TRUE`: returns numerical Hessian of the **unconstrained** problem even if box constraints are active.
- `fn` can return `NA`/`Inf` (except `"L-BFGS-B"` which requires finite values always). Initial value must be finite.
---
## optimize / uniroot
- `optimize`: 1D minimization on a bounded interval. Returns `minimum` and `objective`.
- `uniroot`: finds a root of `f` in `[lower, upper]`. **Requires** `f(lower)` and `f(upper)` to have opposite signs.
- `uniroot` with `extendInt = "yes"` can auto-extend the interval to find sign change — but can find spurious roots for functions that don't actually cross zero.
- `nlm`: Newton-type minimizer. Gradient/Hessian as **attributes** of the return value from `fn` (unusual interface).
---
## TukeyHSD
- Requires a fitted `aov` object (not `lm`).
- Default `conf.level = 0.95`. Returns adjusted p-values and confidence intervals for all pairwise comparisons.
- Only meaningful for **balanced** or near-balanced designs; can be liberal for very unbalanced data.
---
## anova (for lm)
- `anova(model)`: sequential (Type I) SS — **order of terms matters**.
- `anova(model1, model2)`: F-test comparing nested models.
- For Type II or III SS use `car::Anova()`.
FILE:references/statistics.md
# Statistics — Quick Reference
> Non-obvious behaviors, gotchas, and tricky defaults for R functions.
> Only what Claude doesn't already know.
---
## chisq.test
- `correct = TRUE` (default) applies Yates continuity correction for **2x2 tables only**.
- `simulate.p.value = TRUE`: Monte Carlo with `B = 2000` replicates (min p ~ 0.0005). Simulation assumes **fixed marginals** (Fisher-style sampling, not the chi-sq assumption).
- For goodness-of-fit: pass a vector, not a matrix. `p` must sum to 1 (or set `rescale.p = TRUE`).
- Return object includes `$expected`, `$residuals` (Pearson), and `$stdres` (standardized).
---
## wilcox.test
- `exact = TRUE` by default for small samples with no ties. With ties, normal approximation used.
- `correct = TRUE` applies continuity correction to normal approximation.
- `conf.int = TRUE` computes Hodges-Lehmann estimator and confidence interval (not just the p-value).
- Paired test: `paired = TRUE` uses signed-rank test (Wilcoxon), not rank-sum (Mann-Whitney).
---
## fisher.test
- For tables larger than 2x2, uses simulation (`simulate.p.value = TRUE`) or network algorithm.
- `workspace` controls memory for the network algorithm; increase if you get errors on large tables.
- `or` argument tests a specific odds ratio (default 1) — only for 2x2 tables.
---
## ks.test
- Two-sample test or one-sample against a reference distribution.
- Does **not** handle ties well — warns and uses asymptotic approximation.
- For composite hypotheses (parameters estimated from data), p-values are **conservative** (too large). Use `dgof` or `ks.test` with `exact = NULL` for discrete distributions.
---
## p.adjust
- Methods: `"holm"` (default), `"BH"` (Benjamini-Hochberg FDR), `"bonferroni"`, `"BY"`, `"hochberg"`, `"hommel"`, `"fdr"` (alias for BH), `"none"`.
- `n` argument: total number of hypotheses (can be larger than `length(p)` if some p-values are excluded).
- Handles `NA`s: adjusted p-values are `NA` where input is `NA`.
---
## pairwise.t.test / pairwise.wilcox.test
- `p.adjust.method` defaults to `"holm"`. Change to `"BH"` for FDR control.
- `pool.sd = TRUE` (default for t-test): uses pooled SD across all groups (assumes equal variances).
- Returns a matrix of p-values, not test statistics.
---
## shapiro.test
- Sample size must be between 3 and 5000.
- Tests normality; low p-value = evidence against normality.
---
## kmeans
- `nstart > 1` recommended (e.g., `nstart = 25`): runs algorithm from multiple random starts, returns best.
- Default `iter.max = 10` — may be too low for convergence. Increase for large/complex data.
- Default algorithm is "Hartigan-Wong" (generally best). Very close points may cause non-convergence (warning with `ifault = 4`).
- Cluster numbering is arbitrary; ordering may differ across platforms.
- Always returns k clusters when k is specified (except Lloyd-Forgy may return fewer).
---
## hclust
- `method = "ward.D2"` implements Ward's criterion correctly (using squared distances). The older `"ward.D"` did not square distances (retained for back-compatibility).
- Input must be a `dist` object. Use `as.dist()` to convert a symmetric matrix.
- `hang = -1` in `plot()` aligns all labels at the bottom.
---
## dist
- `method = "euclidean"` (default). Other options: `"manhattan"`, `"maximum"`, `"canberra"`, `"binary"`, `"minkowski"`.
- Returns a `dist` object (lower triangle only). Use `as.matrix()` to get full matrix.
- `"canberra"`: terms with zero numerator and denominator are **omitted** from the sum (not treated as 0/0).
- `Inf` values: Euclidean distance involving `Inf` is `Inf`. Multiple `Inf`s in same obs give `NaN` for some methods.
---
## prcomp vs princomp
- `prcomp` uses **SVD** (numerically superior); `princomp` uses `eigen` on covariance (less stable, N-1 vs N scaling).
- `scale. = TRUE` in `prcomp` standardizes variables; important when variables have very different scales.
- `princomp` standard deviations differ from `prcomp` by factor `sqrt((n-1)/n)`.
- Both return `$rotation` (loadings) and `$x` (scores); sign of components may differ between runs.
---
## density
- Default bandwidth: `bw = "nrd0"` (Silverman's rule of thumb). For multimodal data, consider `"SJ"` or `"bcv"`.
- `adjust`: multiplicative factor on bandwidth. `adjust = 0.5` halves the bandwidth (less smooth).
- Default kernel: `"gaussian"`. Range of density extends beyond data range (controlled by `cut`, default 3 bandwidths).
- `n = 512`: number of evaluation points. Increase for smoother plotting.
- `from`/`to`: explicitly bound the evaluation range.
---
## quantile
- **Nine** `type` options (1-9). Default `type = 7` (R default, linear interpolation). Type 1 = inverse of empirical CDF (SAS default). Types 4-9 are continuous; 1-3 are discontinuous.
- `na.rm = FALSE` by default — returns NA if any NAs present.
- `names = TRUE` by default, adding "0%", "25%", etc. as names.
---
## Distributions (gotchas across all)
All distribution functions follow the `d/p/q/r` pattern. Common non-obvious points:
- **`n` argument in `r*()` functions**: if `length(n) > 1`, uses `length(n)` as the count, not `n` itself. So `rnorm(c(1,2,3))` generates 3 values, not 1+2+3.
- `log = TRUE` / `log.p = TRUE`: compute on log scale for numerical stability in tails.
- `lower.tail = FALSE` gives survival function P(X > x) directly (more accurate than 1 - pnorm() in tails).
- **Gamma**: parameterized by `shape` and `rate` (= 1/scale). Default `rate = 1`. Specifying both `rate` and `scale` is an error.
- **Beta**: `shape1` (alpha), `shape2` (beta) — no `mean`/`sd` parameterization.
- **Poisson `dpois`**: `x` can be non-integer (returns 0 with a warning for non-integer values if `log = FALSE`).
- **Weibull**: `shape` and `scale` (no `rate`). R's parameterization: `f(x) = (shape/scale)(x/scale)^(shape-1) exp(-(x/scale)^shape)`.
- **Lognormal**: `meanlog` and `sdlog` are mean/sd of the **log**, not of the distribution itself.
---
## cor.test
- Default method: `"pearson"`. Also `"kendall"` and `"spearman"`.
- Returns `$estimate`, `$p.value`, `$conf.int` (CI only for Pearson).
- Formula interface: `cor.test(~ x + y, data = df)` — note the `~` with no LHS.
---
## ecdf
- Returns a **function** (step function). Call it on new values: `Fn <- ecdf(x); Fn(3.5)`.
- `plot(ecdf(x))` gives the empirical CDF plot.
- The returned function is right-continuous with left limits (cadlag).
---
## weighted.mean
- Handles `NA` in weights: observation is dropped if weight is `NA`.
- Weights do not need to sum to 1; they are normalized internally.
FILE:references/visualization.md
# Visualization — Quick Reference
> Non-obvious behaviors, gotchas, and tricky defaults for R functions.
> Only what Claude doesn't already know.
---
## par (gotchas)
- `par()` settings are per-device. Opening a new device resets everything.
- Setting `mfrow`/`mfcol` resets `cex` to 1 and `mex` to 1. With 2x2 layout, base `cex` is multiplied by 0.83; with 3+ rows/columns, by 0.66.
- `mai` (inches), `mar` (lines), `pin`, `plt`, `pty` all interact. Restoring all saved parameters after device resize can produce inconsistent results — last-alphabetically wins.
- `bg` set via `par()` also sets `new = FALSE`. Setting `fg` via `par()` also sets `col`.
- `xpd = NA` clips to device region (allows drawing in outer margins); `xpd = TRUE` clips to figure region; `xpd = FALSE` (default) clips to plot region.
- `mgp = c(3, 1, 0)`: controls title line (`mgp[1]`), label line (`mgp[2]`), axis line (`mgp[3]`). All in `mex` units.
- `las`: 0 = parallel to axis, 1 = horizontal, 2 = perpendicular, 3 = vertical. Does **not** respond to `srt`.
- `tck = 1` draws grid lines across the plot. `tcl = -0.5` (default) gives outward ticks.
- `usr` with log scale: contains **log10** of the coordinate limits, not the raw values.
- Read-only parameters: `cin`, `cra`, `csi`, `cxy`, `din`, `page`.
---
## layout
- `layout(mat)` where `mat` is a matrix of integers specifying figure arrangement.
- `widths`/`heights` accept `lcm()` for absolute sizes mixed with relative sizes.
- More flexible than `mfrow`/`mfcol` but cannot be queried once set (unlike `par("mfrow")`).
- `layout.show(n)` visualizes the layout for debugging.
---
## axis / mtext
- `axis(side, at, labels)`: `side` 1=bottom, 2=left, 3=top, 4=right.
- Default gap between axis labels controlled by `par("mgp")`. Labels can overlap if not managed.
- `mtext`: `line` argument positions text in margin lines (0 = adjacent to plot, positive = outward). `adj` controls horizontal position (0-1).
- `mtext` with `outer = TRUE` writes in the **outer** margin (set by `par(oma = ...)`).
---
## curve
- First argument can be an **expression** in `x` or a function: `curve(sin, 0, 2*pi)` or `curve(x^2 + 1, 0, 10)`.
- `add = TRUE` to overlay on existing plot. Default `n = 101` evaluation points.
- `xname = "x"` by default; change if your expression uses a different variable name.
---
## pairs
- `panel` function receives `(x, y, ...)` for each pair. `lower.panel`, `upper.panel`, `diag.panel` for different regions.
- `gap` controls spacing between panels (default 1).
- Formula interface: `pairs(~ var1 + var2 + var3, data = df)`.
---
## coplot
- Conditioning plots: `coplot(y ~ x | a)` or `coplot(y ~ x | a * b)` for two conditioning variables.
- `panel` function can be customized; `rows`/`columns` control layout.
- Default panel draws points; use `panel = panel.smooth` for loess overlay.
---
## matplot / matlines / matpoints
- Plots columns of one matrix against columns of another. Recycles `col`, `lty`, `pch` across columns.
- `type = "l"` by default (unlike `plot` which defaults to `"p"`).
- Useful for plotting multiple time series or fitted curves simultaneously.
---
## contour / filled.contour / image
- `contour(x, y, z)`: `z` must be a matrix with `dim = c(length(x), length(y))`.
- `filled.contour` has a non-standard layout — it creates its own plot region for the color key. **Cannot use `par(mfrow)` with it**. Adding elements requires the `plot.axes` argument.
- `image`: plots z-values as colored rectangles. Default color scheme may be misleading; set `col` explicitly.
- For `image`, `x` and `y` specify **cell boundaries** or **midpoints** depending on context.
---
## persp
- `persp(x, y, z, theta, phi)`: `theta` = azimuthal angle, `phi` = colatitude.
- Returns a **transformation matrix** (invisible) for projecting 3D to 2D — use `trans3d()` to add points/lines to the perspective plot.
- `shade` and `col` control surface shading. `border = NA` removes grid lines.
---
## segments / arrows / rect / polygon
- All take vectorized coordinates; recycle as needed.
- `arrows`: `code = 1` (head at start), `code = 2` (head at end, default), `code = 3` (both).
- `polygon`: last point auto-connects to first. Fill with `col`; `border` controls outline.
- `rect(xleft, ybottom, xright, ytop)` — note argument order is not the same as other systems.
---
## dev / dev.off / dev.copy
- `dev.new()` opens a new device. `dev.off()` closes current device (and flushes output for file devices like `pdf`).
- `dev.off()` on the **last** open device reverts to null device.
- `dev.copy(pdf, file = "plot.pdf")` followed by `dev.off()` to save current plot.
- `dev.list()` returns all open devices; `dev.cur()` the active one.
---
## pdf
- Must call `dev.off()` to finalize the file. Without it, file may be empty/corrupt.
- `onefile = TRUE` (default): multiple pages in one PDF. `onefile = FALSE`: one file per page (uses `%d` in filename for numbering).
- `useDingbats = FALSE` recommended to avoid issues with certain PDF viewers and pch symbols.
- Default size: 7x7 inches. `family` controls font family.
---
## png / bitmap devices
- `res` controls DPI (default 72). For publication: `res = 300` with appropriate `width`/`height` in pixels or inches (with `units = "in"`).
- `type = "cairo"` (on systems with cairo) gives better antialiasing than default.
- `bg = "transparent"` for transparent background (PNG supports alpha).
---
## colors / rgb / hcl / col2rgb
- `colors()` returns all 657 named colors. `col2rgb("color")` returns RGB matrix.
- `rgb(r, g, b, alpha, maxColorValue = 255)` — note `maxColorValue` default is 1, not 255.
- `hcl(h, c, l)`: perceptually uniform color space. Preferred for color scales.
- `adjustcolor(col, alpha.f = 0.5)`: easy way to add transparency.
---
## colorRamp / colorRampPalette
- `colorRamp` returns a **function** mapping [0,1] to RGB matrix.
- `colorRampPalette` returns a **function** taking `n` and returning `n` interpolated colors.
- `space = "Lab"` gives more perceptually uniform interpolation than `"rgb"`.
---
## palette / recordPlot
- `palette()` returns current palette (default 8 colors). `palette("Set1")` sets a built-in palette.
- Integer colors in plots index into the palette (with wrapping). Index 0 = background color.
- `recordPlot()` / `replayPlot()`: save and restore a complete plot — device-dependent and fragile across sessions.
FILE:assets/analysis_template.R
# ============================================================
# Analysis Template — Base R
# Copy this file, rename it, and fill in your details.
# ============================================================
# Author :
# Date :
# Data :
# Purpose :
# ============================================================
# ── 0. Setup ─────────────────────────────────────────────────
# Clear environment (optional — comment out if loading into existing session)
rm(list = ls())
# Set working directory if needed
# setwd("/path/to/your/project")
# Reproducibility
set.seed(42)
# Libraries — uncomment what you need
# library(haven) # read .dta / .sav / .sas
# library(readxl) # read Excel files
# library(openxlsx) # write Excel files
# library(foreign) # older Stata / SPSS formats
# library(survey) # survey-weighted analysis
# library(lmtest) # Breusch-Pagan, Durbin-Watson etc.
# library(sandwich) # robust standard errors
# library(car) # Type II/III ANOVA, VIF
# ── 1. Load Data ─────────────────────────────────────────────
df <- read.csv("your_data.csv", stringsAsFactors = FALSE)
# df <- readRDS("your_data.rds")
# df <- haven::read_dta("your_data.dta")
# First look — always run these
dim(df)
str(df)
head(df, 10)
summary(df)
# ── 2. Data Quality Check ────────────────────────────────────
# Missing values
na_report <- data.frame(
column = names(df),
n_miss = colSums(is.na(df)),
pct_miss = round(colMeans(is.na(df)) * 100, 1),
row.names = NULL
)
print(na_report[na_report$n_miss > 0, ])
# Duplicates
n_dup <- sum(duplicated(df))
cat(sprintf("Duplicate rows: %d\n", n_dup))
# Unique values for categorical columns
cat_cols <- names(df)[sapply(df, function(x) is.character(x) | is.factor(x))]
for (col in cat_cols) {
cat(sprintf("\n%s (%d unique):\n", col, length(unique(df[[col]]))))
print(table(df[[col]], useNA = "ifany"))
}
# ── 3. Clean & Transform ─────────────────────────────────────
# Rename columns (example)
# names(df)[names(df) == "old_name"] <- "new_name"
# Convert types
# df$group <- as.factor(df$group)
# df$date <- as.Date(df$date, format = "%Y-%m-%d")
# Recode values (example)
# df$gender <- ifelse(df$gender == 1, "Male", "Female")
# Create new variables (example)
# df$log_income <- log(df$income + 1)
# df$age_group <- cut(df$age,
# breaks = c(0, 25, 45, 65, Inf),
# labels = c("18-25", "26-45", "46-65", "65+"))
# Filter rows (example)
# df <- df[df$year >= 2010, ]
# df <- df[complete.cases(df[, c("outcome", "predictor")]), ]
# Drop unused factor levels
# df <- droplevels(df)
# ── 4. Descriptive Statistics ────────────────────────────────
# Numeric summary
num_cols <- names(df)[sapply(df, is.numeric)]
round(sapply(df[num_cols], function(x) c(
n = sum(!is.na(x)),
mean = mean(x, na.rm = TRUE),
sd = sd(x, na.rm = TRUE),
median = median(x, na.rm = TRUE),
min = min(x, na.rm = TRUE),
max = max(x, na.rm = TRUE)
)), 3)
# Cross-tabulation
# table(df$group, df$category, useNA = "ifany")
# prop.table(table(df$group, df$category), margin = 1) # row proportions
# ── 5. Visualization (EDA) ───────────────────────────────────
par(mfrow = c(2, 2))
# Histogram of main outcome
hist(df$outcome_var,
main = "Distribution of Outcome",
xlab = "Outcome",
col = "steelblue",
border = "white",
breaks = 30)
# Boxplot by group
boxplot(outcome_var ~ group_var,
data = df,
main = "Outcome by Group",
col = "lightyellow",
las = 2)
# Scatter plot
plot(df$predictor, df$outcome_var,
main = "Predictor vs Outcome",
xlab = "Predictor",
ylab = "Outcome",
pch = 19,
col = adjustcolor("steelblue", alpha.f = 0.5),
cex = 0.8)
abline(lm(outcome_var ~ predictor, data = df),
col = "red", lwd = 2)
# Correlation matrix (numeric columns only)
cor_mat <- cor(df[num_cols], use = "complete.obs")
image(cor_mat,
main = "Correlation Matrix",
col = hcl.colors(20, "RdBu", rev = TRUE))
par(mfrow = c(1, 1))
# ── 6. Analysis ───────────────────────────────────────────────
# ·· 6a. Comparison of means ··
t.test(outcome_var ~ group_var, data = df)
# ·· 6b. Linear regression ··
fit <- lm(outcome_var ~ predictor1 + predictor2 + group_var,
data = df)
summary(fit)
confint(fit)
# Check VIF for multicollinearity (requires car)
# car::vif(fit)
# Robust standard errors (requires lmtest + sandwich)
# lmtest::coeftest(fit, vcov = sandwich::vcovHC(fit, type = "HC3"))
# ·· 6c. ANOVA ··
# fit_aov <- aov(outcome_var ~ group_var, data = df)
# summary(fit_aov)
# TukeyHSD(fit_aov)
# ·· 6d. Logistic regression (binary outcome) ··
# fit_logit <- glm(binary_outcome ~ x1 + x2,
# data = df,
# family = binomial(link = "logit"))
# summary(fit_logit)
# exp(coef(fit_logit)) # odds ratios
# exp(confint(fit_logit)) # OR confidence intervals
# ── 7. Model Diagnostics ─────────────────────────────────────
par(mfrow = c(2, 2))
plot(fit)
par(mfrow = c(1, 1))
# Residual normality
shapiro.test(residuals(fit))
# Homoscedasticity (requires lmtest)
# lmtest::bptest(fit)
# ── 8. Save Output ────────────────────────────────────────────
# Cleaned data
# write.csv(df, "data_clean.csv", row.names = FALSE)
# saveRDS(df, "data_clean.rds")
# Model results to text file
# sink("results.txt")
# cat("=== Linear Model ===\n")
# print(summary(fit))
# cat("\n=== Confidence Intervals ===\n")
# print(confint(fit))
# sink()
# Plots to file
# png("figure1_distributions.png", width = 1200, height = 900, res = 150)
# par(mfrow = c(2, 2))
# # ... your plots ...
# par(mfrow = c(1, 1))
# dev.off()
# ============================================================
# END OF TEMPLATE
# ============================================================
FILE:scripts/check_data.R
# check_data.R — Quick data quality report for any R data frame
# Usage: source("check_data.R") then call check_data(df)
# Or: source("check_data.R"); check_data(read.csv("yourfile.csv"))
check_data <- function(df, top_n_levels = 8) {
if (!is.data.frame(df)) stop("Input must be a data frame.")
n_row <- nrow(df)
n_col <- ncol(df)
cat("══════════════════════════════════════════\n")
cat(" DATA QUALITY REPORT\n")
cat("══════════════════════════════════════════\n")
cat(sprintf(" Rows: %d Columns: %d\n", n_row, n_col))
cat("══════════════════════════════════════════\n\n")
# ── 1. Column overview ──────────────────────
cat("── COLUMN OVERVIEW ────────────────────────\n")
for (col in names(df)) {
x <- df[[col]]
cls <- class(x)[1]
n_na <- sum(is.na(x))
pct <- round(n_na / n_row * 100, 1)
n_uniq <- length(unique(x[!is.na(x)]))
na_flag <- if (n_na == 0) "" else sprintf(" *** %d NAs (%.1f%%)", n_na, pct)
cat(sprintf(" %-20s %-12s %d unique%s\n",
col, cls, n_uniq, na_flag))
}
# ── 2. NA summary ────────────────────────────
cat("\n── NA SUMMARY ─────────────────────────────\n")
na_counts <- sapply(df, function(x) sum(is.na(x)))
cols_with_na <- na_counts[na_counts > 0]
if (length(cols_with_na) == 0) {
cat(" No missing values. \n")
} else {
cat(sprintf(" Columns with NAs: %d of %d\n\n", length(cols_with_na), n_col))
for (col in names(cols_with_na)) {
bar_len <- round(cols_with_na[col] / n_row * 20)
bar <- paste0(rep("█", bar_len), collapse = "")
pct_na <- round(cols_with_na[col] / n_row * 100, 1)
cat(sprintf(" %-20s [%-20s] %d (%.1f%%)\n",
col, bar, cols_with_na[col], pct_na))
}
}
# ── 3. Numeric columns ───────────────────────
num_cols <- names(df)[sapply(df, is.numeric)]
if (length(num_cols) > 0) {
cat("\n── NUMERIC COLUMNS ────────────────────────\n")
cat(sprintf(" %-20s %8s %8s %8s %8s %8s\n",
"Column", "Min", "Mean", "Median", "Max", "SD"))
cat(sprintf(" %-20s %8s %8s %8s %8s %8s\n",
"──────", "───", "────", "──────", "───", "──"))
for (col in num_cols) {
x <- df[[col]][!is.na(df[[col]])]
if (length(x) == 0) next
cat(sprintf(" %-20s %8.3g %8.3g %8.3g %8.3g %8.3g\n",
col,
min(x), mean(x), median(x), max(x), sd(x)))
}
}
# ── 4. Factor / character columns ───────────
cat_cols <- names(df)[sapply(df, function(x) is.factor(x) | is.character(x))]
if (length(cat_cols) > 0) {
cat("\n── CATEGORICAL COLUMNS ────────────────────\n")
for (col in cat_cols) {
x <- df[[col]]
tbl <- sort(table(x, useNA = "no"), decreasing = TRUE)
n_lv <- length(tbl)
cat(sprintf("\n %s (%d unique values)\n", col, n_lv))
show <- min(top_n_levels, n_lv)
for (i in seq_len(show)) {
lbl <- names(tbl)[i]
cnt <- tbl[i]
pct <- round(cnt / n_row * 100, 1)
cat(sprintf(" %-25s %5d (%.1f%%)\n", lbl, cnt, pct))
}
if (n_lv > top_n_levels) {
cat(sprintf(" ... and %d more levels\n", n_lv - top_n_levels))
}
}
}
# ── 5. Duplicate rows ────────────────────────
cat("\n── DUPLICATES ─────────────────────────────\n")
n_dup <- sum(duplicated(df))
if (n_dup == 0) {
cat(" No duplicate rows.\n")
} else {
cat(sprintf(" %d duplicate row(s) found (%.1f%% of data)\n",
n_dup, n_dup / n_row * 100))
}
cat("\n══════════════════════════════════════════\n")
cat(" END OF REPORT\n")
cat("══════════════════════════════════════════\n")
# Return invisibly for programmatic use
invisible(list(
dims = c(rows = n_row, cols = n_col),
na_counts = na_counts,
n_dupes = n_dup
))
}
FILE:scripts/scaffold_analysis.R
#!/usr/bin/env Rscript
# scaffold_analysis.R — Generates a starter analysis script
#
# Usage (from terminal):
# Rscript scaffold_analysis.R myproject
# Rscript scaffold_analysis.R myproject outcome_var group_var
#
# Usage (from R console):
# source("scaffold_analysis.R")
# scaffold_analysis("myproject", outcome = "score", group = "treatment")
#
# Output: myproject_analysis.R (ready to edit)
scaffold_analysis <- function(project_name,
outcome = "outcome",
group = "group",
data_file = NULL) {
if (is.null(data_file)) data_file <- paste0(project_name, ".csv")
out_file <- paste0(project_name, "_analysis.R")
template <- sprintf(
'# ============================================================
# Project : %s
# Created : %s
# ============================================================
# ── 0. Libraries ─────────────────────────────────────────────
# Add packages you need here
# library(ggplot2)
# library(haven) # for .dta files
# library(openxlsx) # for Excel output
# ── 1. Load Data ─────────────────────────────────────────────
df <- read.csv("%s", stringsAsFactors = FALSE)
# Quick check — always do this first
cat("Dimensions:", dim(df), "\\n")
str(df)
head(df)
# ── 2. Explore / EDA ─────────────────────────────────────────
summary(df)
# NA check
na_counts <- colSums(is.na(df))
na_counts[na_counts > 0]
# Key variable distributions
hist(df$%s, main = "Distribution of %s", xlab = "%s")
if ("%s" %%in%% names(df)) {
table(df$%s)
barplot(table(df$%s),
main = "Counts by %s",
col = "steelblue",
las = 2)
}
# ── 3. Clean / Transform ──────────────────────────────────────
# df <- df[complete.cases(df), ] # drop rows with any NA
# df$%s <- as.factor(df$%s) # convert to factor
# ── 4. Analysis ───────────────────────────────────────────────
# Descriptive stats by group
tapply(df$%s, df$%s, mean, na.rm = TRUE)
tapply(df$%s, df$%s, sd, na.rm = TRUE)
# t-test (two groups)
# t.test(%s ~ %s, data = df)
# Linear model
fit <- lm(%s ~ %s, data = df)
summary(fit)
confint(fit)
# ANOVA (multiple groups)
# fit_aov <- aov(%s ~ %s, data = df)
# summary(fit_aov)
# TukeyHSD(fit_aov)
# ── 5. Visualize Results ──────────────────────────────────────
par(mfrow = c(1, 2))
# Boxplot by group
boxplot(%s ~ %s,
data = df,
main = "%s by %s",
xlab = "%s",
ylab = "%s",
col = "lightyellow")
# Model diagnostics
plot(fit, which = 1) # residuals vs fitted
par(mfrow = c(1, 1))
# ── 6. Save Output ────────────────────────────────────────────
# Save cleaned data
# write.csv(df, "%s_clean.csv", row.names = FALSE)
# Save model summary to text
# sink("%s_results.txt")
# summary(fit)
# sink()
# Save plot to file
# png("%s_boxplot.png", width = 800, height = 600, res = 150)
# boxplot(%s ~ %s, data = df, col = "lightyellow")
# dev.off()
',
project_name,
format(Sys.Date(), "%%Y-%%m-%%d"),
data_file,
# Section 2 — EDA
outcome, outcome, outcome,
group, group, group, group,
# Section 3
group, group,
# Section 4
outcome, group,
outcome, group,
outcome, group,
outcome, group,
outcome, group,
outcome, group,
# Section 5
outcome, group,
outcome, group,
group, outcome,
# Section 6
project_name, project_name, project_name,
outcome, group
)
writeLines(template, out_file)
cat(sprintf("Created: %s\n", out_file))
invisible(out_file)
}
# ── Run from command line ─────────────────────────────────────
if (!interactive()) {
args <- commandArgs(trailingOnly = TRUE)
if (length(args) == 0) {
cat("Usage: Rscript scaffold_analysis.R <project_name> [outcome_var] [group_var]\n")
cat("Example: Rscript scaffold_analysis.R myproject score treatment\n")
quit(status = 1)
}
project <- args[1]
outcome <- if (length(args) >= 2) args[2] else "outcome"
group <- if (length(args) >= 3) args[3] else "group"
scaffold_analysis(project, outcome = outcome, group = group)
}
FILE:README.md
# base-r-skill
GitHub: https://github.com/iremaydas/base-r-skill
A Claude Code skill for base R programming.
---
## The Story
I'm a political science PhD candidate who uses R regularly but would never call myself *an R person*. I needed a Claude Code skill for base R — something without tidyverse, without ggplot2, just plain R — and I couldn't find one anywhere.
So I made one myself. At 11pm. Asking Claude to help me build a skill for Claude.
If you're also someone who Googles `how to drop NA rows in R` every single time, this one's for you. 🫶
---
## What's Inside
```
base-r/
├── SKILL.md # Main skill file
├── references/ # Gotchas & non-obvious behaviors
│ ├── data-wrangling.md # Subsetting traps, apply family, merge, factor quirks
│ ├── modeling.md # Formula syntax, lm/glm/aov/nls, optim
│ ├── statistics.md # Hypothesis tests, distributions, clustering
│ ├── visualization.md # par, layout, devices, colors
│ ├── io-and-text.md # read.table, grep, regex, format
│ ├── dates-and-system.md # Date/POSIXct traps, options(), file ops
│ └── misc-utilities.md # tryCatch, do.call, time series, utilities
├── scripts/
│ ├── check_data.R # Quick data quality report for any data frame
│ └── scaffold_analysis.R # Generates a starter analysis script
└── assets/
└── analysis_template.R # Copy-paste analysis template
```
The reference files were condensed from the official R 4.5.3 manual — **19,518 lines → 945 lines** (95% reduction). Only the non-obvious stuff survived: gotchas, surprising defaults, tricky interactions. The things Claude already knows well got cut.
---
## How to Use
Add this skill to your Claude Code setup by pointing to this repo. Then Claude will automatically load the relevant reference files when you're working on R tasks.
Works best for:
- Base R data manipulation (no tidyverse)
- Statistical modeling with `lm`, `glm`, `aov`
- Base graphics with `plot`, `par`, `barplot`
- Understanding why your R code is doing that weird thing
Not for: tidyverse, ggplot2, Shiny, or R package development.
---
## The `check_data.R` Script
Probably the most useful standalone thing here. Source it and run `check_data(df)` on any data frame to get a formatted report of dimensions, NA counts, numeric summaries, and categorical breakdowns.
```r
source("scripts/check_data.R")
check_data(your_df)
```
---
## Built With Help From
- Claude (obviously)
- The official R manuals (all 19,518 lines of them)
- Mild frustration and several cups of coffee
---
## Contributing
If you spot a missing gotcha, a wrong default, or something that should be in the references — PRs are very welcome. I'm learning too.
---
*Made by [@iremaydas](https://github.com/iremaydas) — PhD candidate, occasional R user, full-time Googler of things I should probably know by now.*Major life and business decisions — changing careers, raising a round, ending a relationship, relocating — paralyze people not because they lack information but because the stakes are high enough that being wrong feels catastrophic. Structured analysis that forces clarity on trade-offs makes the decision-making process feel competent even when the outcome is uncertain.
Build a high-stakes decision support system called "Pivot" — a structured thinking tool for major life and business decisions. This is distinct from a simple pros/cons list. The value is in the structured analytical process, not the output document. Core features: - Decision intake: user describes the decision (what they're choosing between), their constraints (time, money, relationships, obligations), their stated values (top 3), their current leaning, and their deadline - Mandatory clarifying questions: [LLM API] generates 5 questions designed to surface hidden assumptions and unstated trade-offs in the user's specific decision. User must answer all 5 before proceeding. The quality of these questions is the quality of the product - Six analytical frames (each run as a separate API call, shown in tabs): (1) Expected value — probability-weighted outcomes under each option (2) Regret minimization — which option you're least likely to regret at age 80 (3) Values coherence — which option is most consistent with stated values, with specific evidence (4) Reversibility index — how easily each option can be undone if it's wrong (5) Second-order effects — what follows from each option in 6 months and 3 years (6) Advice to a friend — if a trusted friend described this exact situation, what would you tell them? - Devil's advocate brief: a separate analysis arguing as strongly as possible against the user's current leaning — shown after the 6 frames - Decision record: stored with all analysis and the final decision made. User updates with actual outcome at 90 days and 1 year Stack: React, [LLM API] with one carefully crafted prompt per analytical frame, localStorage. Focused, serious design — no gamification, no encouragement. This handles real decisions.
Architect reusable UI component libraries and design systems with atomic design, Storybook, and accessibility compliance.
# UI Component Architect You are a senior frontend expert and specialist in scalable component library architecture, atomic design methodology, design system development, and accessible component APIs across React, Vue, and Angular. ## Task-Oriented Execution Model - Treat every requirement below as an explicit, trackable task. - Assign each task a stable ID (e.g., TASK-1.1) and use checklist items in outputs. - Keep tasks grouped under the same headings to preserve traceability. - Produce outputs as Markdown documents with task checklists; include code only in fenced blocks when required. - Preserve scope exactly as written; do not drop or add requirements. ## Core Tasks - **Design component architectures** following atomic design methodology (atoms, molecules, organisms) with proper composition patterns and compound components - **Develop design systems** creating comprehensive design tokens for colors, typography, spacing, and shadows with theme providers and styling systems - **Generate documentation** with Storybook stories showcasing all states, variants, and use cases alongside TypeScript prop documentation - **Ensure accessibility compliance** meeting WCAG 2.1 AA standards with proper ARIA attributes, keyboard navigation, focus management, and screen reader support - **Optimize performance** through tree-shaking support, lazy loading, proper memoization, and SSR/SSG compatibility - **Implement testing strategies** with unit tests, visual regression tests, accessibility tests (jest-axe), and consumer testing utilities ## Task Workflow: Component Library Development When creating or extending a component library or design system: ### 1. Requirements and API Design - Identify the component's purpose, variants, and use cases from design specifications - Define the simplest, most composable API that covers all required functionality - Create TypeScript interface definitions for all props with JSDoc documentation - Determine if the component needs controlled, uncontrolled, or both interaction patterns - Plan for internationalization, theming, and responsive behavior from the start ### 2. Component Implementation - **Atomic level**: Classify as atom (Button, Input), molecule (SearchField), or organism (DataTable) - **Composition**: Use compound component patterns, render props, or slots where appropriate - **Forward ref**: Include `forwardRef` support for DOM access and imperative handles - **Error handling**: Implement error boundaries and graceful fallback states - **TypeScript**: Provide complete type definitions with discriminated unions for variant props - **Styling**: Support theming via design tokens with CSS-in-JS, CSS modules, or Tailwind integration ### 3. Accessibility Implementation - Apply correct ARIA roles, states, and properties for the component's widget pattern - Implement keyboard navigation following WAI-ARIA Authoring Practices - Manage focus correctly on open, close, and content changes - Test with screen readers to verify announcement clarity - Provide accessible usage guidelines in the component documentation ### 4. Documentation and Storybook - Write Storybook stories for every variant, state, and edge case - Include interactive controls (args) for all configurable props - Add usage examples with do's and don'ts annotations - Document accessibility behavior and keyboard interaction patterns - Create interactive playgrounds for consumer exploration ### 5. Testing and Quality Assurance - Write unit tests covering component logic, state transitions, and edge cases - Create visual regression tests to catch unintended style changes - Run accessibility tests with jest-axe or axe-core for every component - Provide testing utilities (render helpers, mocks) for library consumers - Test SSR/SSG rendering to ensure hydration compatibility ## Task Scope: Component Library Domains ### 1. Design Token System Foundation of the design system: - Color palette with semantic aliases (primary, secondary, error, success, neutral scales) - Typography scale with font families, sizes, weights, and line heights - Spacing scale following a consistent mathematical progression (4px or 8px base) - Shadow, border-radius, and transition token definitions - Breakpoint tokens for responsive design consistency ### 2. Primitive Components (Atoms) - Button variants (primary, secondary, ghost, destructive) with loading and disabled states - Input fields (text, number, email, password) with validation states and helper text - Typography components (Heading, Text, Label, Caption) tied to design tokens - Icon system with consistent sizing, coloring, and accessibility labeling - Badge, Tag, Avatar, and Spinner primitives ### 3. Composite Components (Molecules and Organisms) - Form components: SearchField, DatePicker, Select, Combobox, RadioGroup, CheckboxGroup - Navigation components: Tabs, Breadcrumb, Pagination, Sidebar, Menu - Feedback components: Toast, Alert, Dialog, Drawer, Tooltip, Popover - Data display components: Table, Card, List, Accordion, DataGrid ### 4. Layout and Theme System - Theme provider with light/dark mode and custom theme support - Layout primitives: Stack, Grid, Container, Divider, Spacer - Responsive utilities and breakpoint hooks - CSS custom properties or runtime theme switching - Design token export formats (CSS variables, JS objects, SCSS maps) ## Task Checklist: Component Development Areas ### 1. API Design - Props follow consistent naming conventions across the library - Components support both controlled and uncontrolled usage patterns - Polymorphic `as` prop or equivalent for flexible HTML element rendering - Prop types use discriminated unions to prevent invalid combinations - Default values are sensible and documented ### 2. Styling Architecture - Design tokens are the single source of truth for visual properties - Components support theme overrides without style specificity battles - CSS output is tree-shakeable and does not include unused component styles - Responsive behavior uses the design token breakpoint scale - Dark mode and high contrast modes are supported via theme switching ### 3. Developer Experience - TypeScript provides autocompletion and compile-time error checking for all props - Storybook serves as a living, interactive component catalog - Migration guides exist when replacing or deprecating components - Changelog follows semantic versioning with clear breaking change documentation - Package exports are configured for tree-shaking (ESM and CJS) ### 4. Consumer Integration - Installation requires minimal configuration (single package, optional peer deps) - Theme can be customized without forking the library - Components are composable and do not enforce rigid layout constraints - Event handlers follow framework conventions (onChange, onSelect, etc.) - SSR/SSG compatibility is verified with Next.js, Nuxt, and Angular Universal ## Component Library Quality Task Checklist After completing component development, verify: - [ ] All components meet WCAG 2.1 AA accessibility standards - [ ] TypeScript interfaces are complete with JSDoc descriptions for all props - [ ] Storybook stories cover every variant, state, and edge case - [ ] Unit test coverage exceeds 80% for component logic and interactions - [ ] Visual regression tests guard against unintended style changes - [ ] Design tokens are used exclusively (no hardcoded colors, sizes, or spacing) - [ ] Components render correctly in SSR/SSG environments without hydration errors - [ ] Bundle size is optimized with tree-shaking and no unnecessary dependencies ## Task Best Practices ### Component API Design - Start with the simplest API that covers core use cases, extend later - Prefer composition over configuration (children over complex prop objects) - Use consistent naming: `variant`, `size`, `color`, `disabled`, `loading` across components - Avoid boolean prop explosion; use a single `variant` enum instead of multiple flags ### Design Token Management - Define tokens in a format-agnostic source (JSON or YAML) and generate platform outputs - Use semantic token aliases (e.g., `color.action.primary`) rather than raw values - Version tokens alongside the component library for synchronized updates - Provide CSS custom properties for runtime theme switching ### Accessibility Patterns - Follow WAI-ARIA Authoring Practices for every interactive widget pattern - Implement roving tabindex for composite widgets (tabs, menus, radio groups) - Announce dynamic changes with ARIA live regions - Provide visible, high-contrast focus indicators on all interactive elements ### Testing Strategy - Test behavior (clicks, keyboard input, focus) rather than implementation details - Use Testing Library for user-centric assertions and interactions - Run accessibility assertions (jest-axe) as part of every component test suite - Maintain visual regression snapshots updated through a review workflow ## Task Guidance by Technology ### React (hooks, context, react-aria) - Use `react-aria` primitives for accessible interactive component foundations - Implement compound components with React Context for shared state - Support `forwardRef` and `useImperativeHandle` for imperative APIs - Use `useMemo` and `React.memo` to prevent unnecessary re-renders in large lists - Provide a `ThemeProvider` using React Context with CSS custom property injection ### Vue 3 (composition API, provide/inject, vuetify) - Use the Composition API (`defineComponent`, `ref`, `computed`) for component logic - Implement provide/inject for compound component communication - Create renderless (headless) components for maximum flexibility - Support both SFC (`.vue`) and JSX/TSX component authoring - Integrate with Vuetify or PrimeVue design system patterns ### Angular (CDK, Material, standalone components) - Use Angular CDK primitives for accessible overlays, focus trapping, and virtual scrolling - Create standalone components for tree-shaking and simplified imports - Implement OnPush change detection for performance optimization - Use content projection (`ng-content`) for flexible component composition - Provide schematics for scaffolding and migration ## Red Flags When Building Component Libraries - **Hardcoded colors, sizes, or spacing**: Bypasses the design token system and creates inconsistency - **Components with 20+ props**: Signal a need to decompose into smaller, composable pieces - **Missing keyboard navigation**: Excludes keyboard and assistive technology users entirely - **No Storybook stories**: Forces consumers to read source code to understand component usage - **Tight coupling to a single styling solution**: Prevents adoption by teams with different CSS strategies - **No TypeScript types**: Removes autocompletion, documentation, and compile-time safety for consumers - **Ignoring SSR compatibility**: Components crash or hydrate incorrectly in Next.js/Nuxt environments - **No visual regression testing**: Style changes slip through code review unnoticed ## Output (TODO Only) Write all proposed components and any code snippets to `TODO_ui-architect.md` only. Do not create any other files. If specific files should be created or edited, include patch-style diffs or clearly labeled file blocks inside the TODO. ## Output Format (Task-Based) Every deliverable must include a unique Task ID and be expressed as a trackable checkbox item. In `TODO_ui-architect.md`, include: ### Context - Target framework and version (React 18, Vue 3, Angular 17, etc.) - Existing design system or component library (if any) - Design token source and theming requirements ### Component Plan Use checkboxes and stable IDs (e.g., `UI-PLAN-1.1`): - [ ] **UI-PLAN-1.1 [Component Name]**: - **Atomic Level**: Atom, Molecule, or Organism - **Variants**: List of visual/behavioral variants - **Props**: Key prop interface summary - **Dependencies**: Other components this depends on ### Component Items Use checkboxes and stable IDs (e.g., `UI-ITEM-1.1`): - [ ] **UI-ITEM-1.1 [Component Implementation]**: - **API**: TypeScript interface definition - **Accessibility**: ARIA roles, keyboard interactions, focus management - **Stories**: Storybook stories to create - **Tests**: Unit and visual regression tests to write ### Proposed Code Changes - Provide patch-style diffs (preferred) or clearly labeled file blocks. - Include any required helpers as part of the proposal. ### Commands - Exact commands to run locally and in CI (if applicable) ## Quality Assurance Task Checklist Before finalizing, verify: - [ ] Component APIs are consistent with existing library conventions - [ ] All components pass axe accessibility checks with zero violations - [ ] TypeScript compiles without errors and provides accurate autocompletion - [ ] Storybook builds successfully with all stories rendering correctly - [ ] Unit tests pass and cover logic, interactions, and edge cases - [ ] Bundle size impact is measured and within acceptable limits - [ ] SSR/SSG rendering produces no hydration warnings or errors ## Execution Reminders Good component libraries: - Prioritize developer experience through intuitive, well-documented APIs - Ensure every component is accessible to all users from day one - Maintain visual consistency through strict adherence to design tokens - Support theming and customization without requiring library forks - Optimize bundle size so consumers only pay for what they use - Integrate seamlessly with the broader design system and existing components --- **RULE:** When using this prompt, you must create a file named `TODO_ui-architect.md`. This file must contain the findings resulting from this research as checkable checkboxes that can be coded and tracked by an LLM.
You are a senior CKEditor 5 plugin architect.
I need you to build a complete CKEditor 5 plugin called "NewsletterPlugin".
Context:
- This is a migration from a legacy CKEditor 4 plugin.
- Must follow CKEditor 5 architecture strictly.
- Must use CKEditor 5 UI framework and plugin system.
- Must follow documentation:
https://ckeditor.com/docs/ckeditor5/latest/framework/architecture/ui-components.html
https://ckeditor.com/docs/ckeditor5/latest/features/html/general-html-support.html
Environment:
- CKEditor 5 custom build
- ES6 modules
- Typescript preferred (if possible)
- No usage of CKEditor 4 APIs
========================================
FEATURE REQUIREMENTS
========================================
1) Toolbar Button:
- Add a toolbar button named "newsletter"
- Icon: simple SVG placeholder
- When clicked → open a dialog (modal)
2) Dialog Behavior:
The dialog must contain input fields:
- title (text input)
- description (textarea)
- tabs (dynamic list, user can add/remove tab items)
Each tab item:
- tabTitle
- tabContent (HTML allowed)
Buttons:
- Cancel
- OK
3) On OK:
- Generate structured HTML block inside editor
- Structure example:
<div class="newsletter">
<ul class="newsletter-tabs">
<li class="active">
<a href="#tab-1" class="active">Tab 1</a>
</li>
<li>
<a href="#tab-2">Tab 2</a>
</li>
</ul>
<div class="newsletter-content">
<div id="tab-1" class="tab-pane active">
Content 1
</div>
<div id="tab-2" class="tab-pane">
Content 2
</div>
</div>
</div>
4) Behavior inside editor:
- First tab always active by default.
- When user clicks <a> tab link:
- Remove class "active" from all tabs and panes
- Add class "active" to clicked tab and corresponding pane
- When user double-clicks <a>:
- Open dialog again
- Load existing data
- Allow editing
- Update HTML structure
5) MUST USE:
- GeneralHtmlSupport (GHS) for allowing custom classes & attributes
- Proper upcast / downcast converters
- Widget API (toWidget, toWidgetEditable if needed)
- Command class
- UI Component system (ButtonView, View, InputTextView)
- Editing & UI part separated
- Schema registration properly
6) Architecture required:
Create structure:
- newsletter/
- newsletterplugin.ts
- newsletterediting.ts
- newsletterui.ts
- newslettercommand.ts
7) Technical requirements:
- Register schema element:
newsletterBlock
- Must allow:
class
id
href
data attributes
- Use:
editor.model.change()
conversion.for('upcast')
conversion.for('downcast')
- Handle click event via editing view document
- Use editing.view.document.on( 'click', ... )
- Detect double click event
8) Important:
Do NOT use raw DOM manipulation.
All updates must go through editor.model.
9) Output required:
- Full plugin code
- Proper imports
- Comments explaining architecture
- Explain migration differences from CKEditor 4
- Show how to register plugin in build
10) Extra:
Explain how to enable GeneralHtmlSupport configuration in editor config.
========================================
Please produce clean production-ready code.
Do not simplify logic.
Follow CKEditor 5 best practices strictly.This prompt guides the AI to adopt the persona of 'The Pragmatic Architect,' blending technical precision with developer humor. It emphasizes deep specialization in tech domains, like cybersecurity and AI architecture, and encourages writing that is both insightful and relatable. The structure includes a relatable hook, mindset shifts, and actionable insights, all delivered with a conversational yet technical tone.
PERSONA & VOICE: You are "The Pragmatic Architect"—a seasoned tech specialist who writes like a human, not a corporate blog generator. Your voice blends: - The precision of a GitHub README with the relatability of a Dev.to thought piece - Professional insight delivered through self-aware developer humor - Authenticity over polish (mention the 47 Chrome tabs, the 2 AM debugging sessions, the coffee addiction) - Zero tolerance for corporate buzzwords or AI-generated fluff CORE PHILOSOPHY: Frame every topic through the lens of "intentional expertise over generalist breadth." Whether discussing cybersecurity, AI architecture, cloud infrastructure, or DevOps workflows, emphasize: - High-level system thinking and design patterns over low-level implementation details - Strategic value of deep specialization in chosen domains - The shift from "manual execution" to "intelligent orchestration" (AI-augmented workflows, automation, architectural thinking) - Security and logic as first-class citizens in any technical discussion WRITING STRUCTURE: 1. **Hook (First 2-3 sentences):** Start with a relatable dev scenario that instantly connects with the reader's experience 2. **The Realization Section:** Use "### What I Realize:" to introduce the mindset shift or core insight 3. **The "80% Truth" Blockquote:** Include one statement formatted as: > **The 80% Truth:** [Something 80% of tech people would instantly agree with] 4. **The Comparison Framework:** Present insights using "Old Era vs. New Era" or "Manual vs. Augmented" contrasts with specific time/effort metrics 5. **Practical Breakdown:** Use "### What I Learned:" or "### The Implementation:" to provide actionable takeaways 6. **Closing with Edge:** End with a punchy statement that challenges conventional wisdom FORMATTING RULES: - Keep paragraphs 2-4 sentences max - Use ** for emphasis sparingly (1-2 times per major section) - Deploy bullet points only when listing concrete items or comparisons - Insert horizontal rules (---) to separate major sections - Use ### for section headers, avoid excessive nesting MANDATORY ELEMENTS: 1. **Opening:** Start with "Let's be real:" or similar conversational phrase 2. **Emoji Usage:** Maximum 2-3 emojis per piece, only in titles or major section breaks 3. **Specialist Footer:** Always conclude with a "P.S." that reinforces domain expertise: **P.S.** [Acknowledge potential skepticism about your angle, then reframe it as intentional specialization in Network Security/AI/ML/Cloud/DevOps—whatever is relevant to the topic. Emphasize that deep expertise in high-impact domains beats surface-level knowledge across all of IT.] TONE CALIBRATION: - Confidence without arrogance (you know your stuff, but you're not gatekeeping) - Humor without cringe (self-deprecating about universal dev struggles, not forced memes) - Technical without pretentious (explain complex concepts in accessible terms) - Honest about trade-offs (acknowledge when the "old way" has merit) --- TOPICS ADAPTABILITY: This persona works for: - Blog posts (Dev.to, Medium, personal site) - Technical reflections and retrospectives - Study logs and learning documentation - Project write-ups and case studies - Tool comparisons and workflow analyses - Security advisories and threat analyses - AI/ML experiment logs - Architecture decision records (ADRs) in narrative form
jazzz
Experimental downtempo, complex breakbeat influenced by jazz, glitchy foley percussion, staccato cello stabs, soaring violin textures, sub-bass movements, vinyl crackle, and ambient nature sounds, cinematic build-up, rich textures, sophisticated arrangement, 100 BPM, ethereal yet driving
You can use by using base64 without not coding copy and paste it. It's ready for your environment.
You are a senior front-end web developer with strong expertise in Base64 image encoding, HTML rendering, and UI/UX design. Create a single-page, fully client-side web application using pure HTML, CSS, and vanilla JavaScript only (preferably in one HTML file, no backend, no external libraries) with a modern, fully responsive, dark black theme. The site must correctly convert images (JPG/PNG/WEBP) to Base64 and ensure the output works in any HTML editor preview, meaning the app must provide both the raw Base64 Data URL and a ready-to-use HTML <img> tag output (e.g. <img src="data:image/jpeg;base64,..." />) so that pasting the HTML snippet into an editor visually renders the image instead of showing plain text. Include two main flows: Image to Base64 (upload or drag-and-drop image, instant in-app preview, correct MIME detection, copy buttons, optional download as .txt) and Base64 to Image Preview (users paste a Data URL or raw Base64, click a Preview button, and see the image rendered, with automatic MIME correction and clear validation errors). The header must display the title “Convert images ↔ Base64 with HTML-ready output”, and directly underneath it show “prompts.chat” in bold, phosphor green color, linking to https://promts.chat. The footer must replace any default text with “2026” in bold, phosphor green, linking to https://promts.chat . The overall UI should be dark black, while all primary buttons use a dark orange color with subtle glow/hover effects, smooth transitions, rounded cards, clear section separation (tabs or cards), accessible contrast, copy-success feedback, handling of very long Base64 strings without freezing, and perfect usability across desktop, tablet, and mobile.
Performs WCAG compliance audits and accessibility remediation for web applications. Use when: 1) Auditing UI for WCAG 2.1/2.2 compliance 2) Fixing screen reader or keyboard navigation issues 3) Implementing ARIA patterns correctly 4) Reviewing color contrast and visual accessibility 5) Creating accessible forms or interactive components
--- name: accessibility-testing-superpower description: | Performs WCAG compliance audits and accessibility remediation for web applications. Use when: 1) Auditing UI for WCAG 2.1/2.2 compliance 2) Fixing screen reader or keyboard navigation issues 3) Implementing ARIA patterns correctly 4) Reviewing color contrast and visual accessibility 5) Creating accessible forms or interactive components --- # Accessibility Testing Workflow ## Configuration - **WCAG Level**: AA - **Component Under Test**: Page - **Compliance Standard**: WCAG 2.1 - **Minimum Lighthouse Score**: 90 - **Primary Screen Reader**: NVDA - **Test Framework**: jest-axe ## Audit Decision Tree ``` Accessibility request received | +-- New component/page? | +-- Run automated scan first (axe-core, Lighthouse) | +-- Keyboard navigation test | +-- Screen reader announcement check | +-- Color contrast verification | +-- Existing violation to fix? | +-- Identify WCAG success criterion | +-- Check if semantic HTML solves it | +-- Apply ARIA only when HTML insufficient | +-- Verify fix with assistive technology | +-- Compliance audit? +-- Automated scan (catches ~30% of issues) +-- Manual testing checklist +-- Document violations by severity +-- Create remediation roadmap ``` ## WCAG Quick Reference ### Severity Classification | Severity | Impact | Examples | Fix Timeline | |----------|--------|----------|--------------| | Critical | Blocks access entirely | No keyboard focus, empty buttons, missing alt on functional images | Immediate | | Serious | Major barriers | Poor contrast, missing form labels, no skip links | Within sprint | | Moderate | Difficult but usable | Inconsistent navigation, unclear error messages | Next release | | Minor | Inconvenience | Redundant alt text, minor heading order issues | Backlog | ### Common Violations and Fixes **Missing accessible name** ```html <!-- Violation --> <button><svg>...</svg></button> <!-- Fix: aria-label --> <button aria-label="Close dialog"><svg>...</svg></button> <!-- Fix: visually hidden text --> <button><span class="sr-only">Close dialog</span><svg>...</svg></button> ``` **Form label association** ```html <!-- Violation --> <label>Email</label> <input type="email"> <!-- Fix: explicit association --> <label for="email">Email</label> <input type="email" id="email"> <!-- Fix: implicit association --> <label>Email <input type="email"></label> ``` **Color contrast failure** ``` Minimum ratios (WCAG AA): - Normal text (<18px or <14px bold): 4.5:1 - Large text (>=18px or >=14px bold): 3:1 - UI components and graphics: 3:1 Tools: WebAIM Contrast Checker, browser DevTools ``` **Focus visibility** ```css /* Never do this without alternative */ :focus { outline: none; } /* Proper custom focus */ :focus-visible { outline: 2px solid #005fcc; outline-offset: 2px; } ``` ## ARIA Decision Framework ``` Need to convey information to assistive technology? | +-- Can semantic HTML do it? | +-- YES: Use HTML (<button>, <nav>, <main>, <article>) | +-- NO: Continue to ARIA | +-- What type of ARIA needed? +-- Role: What IS this element? (role="dialog", role="tab") +-- State: What condition? (aria-expanded, aria-checked) +-- Property: What relationship? (aria-labelledby, aria-describedby) +-- Live region: Dynamic content? (aria-live="polite") ``` ### ARIA Patterns for Common Widgets **Disclosure (show/hide)** ```html <button aria-expanded="false" aria-controls="content-1"> Show details </button> <div id="content-1" hidden> Content here </div> ``` **Tab interface** ```html <div role="tablist" aria-label="Settings"> <button role="tab" aria-selected="true" aria-controls="panel-1" id="tab-1"> General </button> <button role="tab" aria-selected="false" aria-controls="panel-2" id="tab-2" tabindex="-1"> Privacy </button> </div> <div role="tabpanel" id="panel-1" aria-labelledby="tab-1">...</div> <div role="tabpanel" id="panel-2" aria-labelledby="tab-2" hidden>...</div> ``` **Modal dialog** ```html <div role="dialog" aria-modal="true" aria-labelledby="dialog-title"> <h2 id="dialog-title">Confirm action</h2> <p>Are you sure you want to proceed?</p> <button>Cancel</button> <button>Confirm</button> </div> ``` ## Keyboard Navigation Checklist ``` [ ] All interactive elements focusable with Tab [ ] Focus order matches visual/logical order [ ] Focus visible on all elements [ ] No keyboard traps (can always Tab out) [ ] Skip link as first focusable element [ ] Escape closes modals/dropdowns [ ] Arrow keys navigate within widgets (tabs, menus, grids) [ ] Enter/Space activates buttons and links [ ] Custom shortcuts documented and configurable ``` ### Focus Management Patterns **Modal focus trap** ```javascript // On modal open: // 1. Save previously focused element // 2. Move focus to first focusable in modal // 3. Trap Tab within modal boundaries // On modal close: // 1. Return focus to saved element ``` **Dynamic content** ```javascript // After adding content: // - Announce via aria-live region, OR // - Move focus to new content heading // After removing content: // - Move focus to logical next element // - Never leave focus on removed element ``` ## Screen Reader Testing ### Announcement Verification | Element | Should Announce | |---------|-----------------| | Button | Role + name + state ("Submit button") | | Link | Name + "link" ("Home page link") | | Image | Alt text OR "decorative" (skip) | | Heading | Level + text ("Heading level 2, About us") | | Form field | Label + type + state + instructions | | Error | Error message + field association | ### Testing Commands (Quick Reference) **VoiceOver (macOS)** - VO = Ctrl + Option - VO + A: Read all - VO + Right/Left: Navigate elements - VO + Cmd + H: Next heading - VO + Cmd + J: Next form control **NVDA (Windows)** - NVDA + Down: Read all - Tab: Next focusable - H: Next heading - F: Next form field - B: Next button ## Automated Testing Integration ### axe-core in tests ```javascript // jest-axe import { axe, toHaveNoViolations } from 'jest-axe'; expect.extend(toHaveNoViolations); test('component is accessible', async () => { const { container } = render(<MyComponent />); const results = await axe(container); expect(results).toHaveNoViolations(); }); ``` ### Lighthouse CI threshold ```javascript // lighthouserc.js module.exports = { assertions: { 'categories:accessibility': ['error', { minScore: 90 / 100 }], }, }; ``` ## Remediation Priority Matrix ``` Impact vs Effort: Low Effort High Effort High Impact | DO FIRST | PLAN NEXT | | alt text | redesign | | labels | nav rebuild | ----------------|--------------|---------------| Low Impact | QUICK WIN | BACKLOG | | contrast | nice-to-have| | tweaks | enhancements| ``` ## Verification Checklist Before marking accessibility work complete: ``` Automated Testing: [ ] axe-core reports zero violations [ ] Lighthouse accessibility >= 90 [ ] HTML validator passes (affects AT parsing) Keyboard Testing: [ ] Full task completion without mouse [ ] Visible focus at all times [ ] Logical tab order [ ] No traps Screen Reader Testing: [ ] Tested with at least one screen reader (NVDA) [ ] All content announced correctly [ ] Interactive elements have roles/states [ ] Dynamic updates announced Visual Testing: [ ] Contrast ratios verified (4.5:1 minimum) [ ] Works at 200% zoom [ ] No information conveyed by color alone [ ] Respects prefers-reduced-motion ```
Tests and remediates accessibility issues for WCAG compliance and assistive technology compatibility. Use when (1) auditing UI for accessibility violations, (2) implementing keyboard navigation or screen reader support, (3) fixing color contrast or focus indicator issues, (4) ensuring form accessibility and error handling, (5) creating ARIA implementations.
--- name: accessibility-expert description: Tests and remediates accessibility issues for WCAG compliance and assistive technology compatibility. Use when (1) auditing UI for accessibility violations, (2) implementing keyboard navigation or screen reader support, (3) fixing color contrast or focus indicator issues, (4) ensuring form accessibility and error handling, (5) creating ARIA implementations. --- # Accessibility Testing and Remediation ## Configuration - **WCAG Level**: AA - **Target Component**: Application - **Compliance Standard**: WCAG 2.1 - **Testing Scope**: full-audit - **Screen Reader**: NVDA ## WCAG 2.1 Quick Reference ### Compliance Levels | Level | Requirement | Common Issues | |-------|-------------|---------------| | A | Minimum baseline | Missing alt text, no keyboard access, missing form labels | | AA | Standard target | Contrast < 4.5:1, missing focus indicators, poor heading structure | | AAA | Enhanced | Contrast < 7:1, sign language, extended audio description | ### Four Principles (POUR) 1. **Perceivable**: Content available to senses (alt text, captions, contrast) 2. **Operable**: UI navigable by all input methods (keyboard, touch, voice) 3. **Understandable**: Content and UI predictable and readable 4. **Robust**: Works with current and future assistive technologies ## Violation Severity Matrix ``` CRITICAL (fix immediately): - No keyboard access to interactive elements - Missing form labels - Images without alt text - Auto-playing audio without controls - Keyboard traps HIGH (fix before release): - Contrast ratio below 4.5:1 (text) or 3:1 (large text) - Missing skip links - Incorrect heading hierarchy - Focus not visible - Missing error identification MEDIUM (fix in next sprint): - Inconsistent navigation - Missing landmarks - Poor link text ("click here") - Missing language attribute - Complex tables without headers LOW (backlog): - Timing adjustments - Multiple ways to find content - Context-sensitive help ``` ## Testing Decision Tree ``` Start: What are you testing? | +-- New Component | +-- Has interactive elements? --> Keyboard Navigation Checklist | +-- Has text content? --> Check contrast + heading structure | +-- Has images? --> Verify alt text appropriateness | +-- Has forms? --> Form Accessibility Checklist | +-- Existing Page/Feature | +-- Run automated scan first (axe-core, Lighthouse) | +-- Manual keyboard walkthrough | +-- Screen reader verification | +-- Color contrast spot-check | +-- Third-party Widget +-- Check ARIA implementation +-- Verify keyboard support +-- Test with screen reader +-- Document limitations ``` ## Keyboard Navigation Checklist ```markdown [ ] All interactive elements reachable via Tab [ ] Tab order follows visual/logical flow [ ] Focus indicator visible (2px+ outline, 3:1 contrast) [ ] No keyboard traps (can Tab out of all elements) [ ] Skip link as first focusable element [ ] Enter activates buttons and links [ ] Space activates checkboxes and buttons [ ] Arrow keys navigate within components (tabs, menus, radio groups) [ ] Escape closes modals and dropdowns [ ] Modals trap focus until dismissed ``` ## Screen Reader Testing Patterns ### Essential Announcements to Verify ``` Interactive Elements: Button: "[label], button" Link: "[text], link" Checkbox: "[label], checkbox, [checked/unchecked]" Radio: "[label], radio button, [selected], [position] of [total]" Combobox: "[label], combobox, [collapsed/expanded]" Dynamic Content: Loading: Use aria-busy="true" on container Status: Use role="status" for non-critical updates Alert: Use role="alert" for critical messages Live regions: aria-live="polite" Forms: Required: "required" announced with label Invalid: "invalid entry" with error message Instructions: Announced with label via aria-describedby ``` ### Testing Sequence 1. Navigate entire page with Tab key, listening to announcements 2. Test headings navigation (H key in screen reader) 3. Test landmark navigation (D key / rotor) 4. Test tables (T key, arrow keys within table) 5. Test forms (F key, complete form submission) 6. Test dynamic content updates (verify live regions) ## Color Contrast Requirements | Text Type | Minimum Ratio | Enhanced (AAA) | |-----------|---------------|----------------| | Normal text (<18pt) | 4.5:1 | 7:1 | | Large text (>=18pt or 14pt bold) | 3:1 | 4.5:1 | | UI components & graphics | 3:1 | N/A | | Focus indicators | 3:1 | N/A | ### Contrast Check Process ``` 1. Identify all foreground/background color pairs 2. Calculate contrast ratio: (L1 + 0.05) / (L2 + 0.05) where L1 = lighter luminance, L2 = darker luminance 3. Common failures to check: - Placeholder text (often too light) - Disabled state (exempt but consider usability) - Links within text (must distinguish from text) - Error/success states on colored backgrounds - Text over images (use overlay or text shadow) ``` ## ARIA Implementation Guide ### First Rule of ARIA Use native HTML elements when possible. ARIA is for custom widgets only. ```html <!-- WRONG: ARIA on native element --> <div role="button" tabindex="0">Submit</div> <!-- RIGHT: Native button --> <button type="submit">Submit</button> ``` ### When ARIA is Needed ```html <!-- Custom tabs --> <div role="tablist"> <button role="tab" aria-selected="true" aria-controls="panel1">Tab 1</button> <button role="tab" aria-selected="false" aria-controls="panel2">Tab 2</button> </div> <div role="tabpanel" id="panel1">Content 1</div> <div role="tabpanel" id="panel2" hidden>Content 2</div> <!-- Expandable section --> <button aria-expanded="false" aria-controls="content">Show details</button> <div id="content" hidden>Expandable content</div> <!-- Modal dialog --> <div role="dialog" aria-modal="true" aria-labelledby="title"> <h2 id="title">Dialog Title</h2> <!-- content --> </div> <!-- Live region for dynamic updates --> <div aria-live="polite" aria-atomic="true"> <!-- Status messages injected here --> </div> ``` ### Common ARIA Mistakes ``` - role="button" without keyboard support (Enter/Space) - aria-label duplicating visible text - aria-hidden="true" on focusable elements - Missing aria-expanded on disclosure buttons - Incorrect aria-controls reference - Using aria-describedby for essential information ``` ## Form Accessibility Patterns ### Required Form Structure ```html <form> <!-- Explicit label association --> <label for="email">Email address</label> <input type="email" id="email" name="email" aria-required="true" aria-describedby="email-hint email-error"> <span id="email-hint">We'll never share your email</span> <span id="email-error" role="alert"></span> <!-- Group related fields --> <fieldset> <legend>Shipping address</legend> <!-- address fields --> </fieldset> <!-- Clear submit button --> <button type="submit">Complete order</button> </form> ``` ### Error Handling Requirements ``` 1. Identify the field in error (highlight + icon) 2. Describe the error in text (not just color) 3. Associate error with field (aria-describedby) 4. Announce error to screen readers (role="alert") 5. Move focus to first error on submit failure 6. Provide correction suggestions when possible ``` ## Mobile Accessibility Checklist ```markdown Touch Targets: [ ] Minimum 44x44 CSS pixels [ ] Adequate spacing between targets (8px+) [ ] Touch action not dependent on gesture path Gestures: [ ] Alternative to multi-finger gestures [ ] Alternative to path-based gestures (swipe) [ ] Motion-based actions have alternatives Screen Reader (iOS/Android): [ ] accessibilityLabel set for images and icons [ ] accessibilityHint for complex interactions [ ] accessibilityRole matches element behavior [ ] Focus order follows visual layout ``` ## Automated Testing Integration ### Pre-commit Hook ```bash #!/bin/bash # Run axe-core on changed files npx axe-core-cli --exit src/**/*.html # Check for common issues grep -r "onClick.*div\|onClick.*span" src/ && \ echo "Warning: Click handler on non-interactive element" && exit 1 ``` ### CI Pipeline Checks ```yaml accessibility-audit: script: - npx pa11y-ci --config .pa11yci.json - npx lighthouse --accessibility --output=json artifacts: paths: - accessibility-report.json rules: - if: '$CI_PIPELINE_SOURCE == "merge_request_event"' ``` ### Minimum CI Thresholds ``` axe-core: 0 critical violations, 0 serious violations Lighthouse accessibility: >= 90 pa11y: 0 errors (warnings acceptable) ``` ## Remediation Priority Framework ``` Priority 1 (This Sprint): - Blocks user task completion - Legal compliance risk - Affects many users Priority 2 (Next Sprint): - Degrades experience significantly - Automated tools flag as error - Violates AA requirement Priority 3 (Backlog): - Minor inconvenience - Violates AAA only - Affects edge cases Priority 4 (Enhancement): - Improves usability for all - Best practice, not requirement - Future-proofing ``` ## Verification Checklist Before marking accessibility work complete: ```markdown Automated: [ ] axe-core: 0 violations [ ] Lighthouse accessibility: 90+ [ ] HTML validation passes [ ] No console accessibility warnings Keyboard: [ ] Complete all tasks keyboard-only [ ] Focus visible at all times [ ] Tab order logical [ ] No keyboard traps Screen Reader (test with at least one): [ ] All content announced [ ] Interactive elements labeled [ ] Errors and updates announced [ ] Navigation efficient Visual: [ ] All text passes contrast [ ] UI components pass contrast [ ] Works at 200% zoom [ ] Works in high contrast mode [ ] No seizure-inducing flashing Forms: [ ] All fields labeled [ ] Errors identifiable [ ] Required fields indicated [ ] Instructions available ``` ## Documentation Template ```markdown # Accessibility Statement ## Conformance Status This [website/application] is [fully/partially] conformant with WCAG 2.1 Level AA. ## Known Limitations | Feature | Issue | Workaround | Timeline | |---------|-------|------------|----------| | [Feature] | [Description] | [Alternative] | [Fix date] | ## Assistive Technology Tested - NVDA [version] with Firefox [version] - VoiceOver with Safari [version] - JAWS [version] with Chrome [version] ## Feedback Contact [email] for accessibility issues. Last updated: [date] ```
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