| name | commenting |
| description | Universal commenting and documentation conventions across all languages. Load when writing or reviewing substantial comments, docstrings, file headers, or migration documentation. Project-specific commenting standards in `docs/commenting-standard.md` (when present) extend or override this baseline. |
Commenting standard (universal)
Comments are part of the codebase. Write fewer; make them count.
The core rule
Comments explain why, code explains what. If a comment just restates the code, delete it and rename the variable, function, component, or file. A good identifier eliminates the need for the comment.
Write comments for
- Intent and rationale. Why this approach, not the obvious alternative.
- Non-obvious constraints. Rate limits, race conditions, API quirks, hidden invariants, regulatory requirements, expand-contract migration phases.
- Warnings. "Do not call without holding the lock," "mutates input," "raw body required for signature verification," "must run before any Sentry init."
- Links. Issue numbers, RFC / spec references, vendor docs, blueprint sections, CVE IDs.
- TODO / FIXME / HACK / XXX tags with an author and a tracking reference:
// TODO(av1155, BAI-247): restore jsx-a11y rules once v7 ships. A bare // TODO is dead weight.
- Citations in compliance, financial, or legal code. Name the regulation, PPM section, treaty article, or blueprint section. These are part of the audit trail.
Avoid
- Restating code (
const i = 0; // initialize i).
- Commented-out code. Use git; delete it.
- Changelog-style narration (
// 2026-04-15: fixed bug). That belongs in the commit message.
- Discovery narration (
// it took a live incident to find this, // after debugging we realized..., // we originally tried X but...). State the constraint; reference the ticket. The story belongs in the PR description or postmortem, not the source.
- Decorative banners (
// ===== SECTION =====). Module structure already does this. SQL migrations and globals.css are the documented exceptions where banners help readability.
- Stale comments. When you change code, update or remove the comment.
- Apologetic comments (
// this is hacky but...). Either fix it or open a ticket.
- Obvious type / name duplication (
amountCents: number; // amount in cents).
- AI-edit narration (
// Claude refactored this from useEffect to useReducer). The diff already shows it.
- Process-theater language (
// verified, // post-fix verification).
- Long explanations or tutorials. If it needs a tutorial, write a doc and link to it.
Per-language doc style
- TypeScript / JavaScript: TSDoc on exported symbols (functions, types, components, hooks, schemas). Inline
// for short notes. Two leading spaces before inline //. Never duplicate a TypeScript signature inside the doc; the signature is the source of truth. Forbidden tags: @type, inline @param {type} (TypeScript already owns types). See the typescript rule for full details.
- Python: PEP 257 + Google-style docstrings (Sphinx Napoleon). Imperative mood ("Return X", not "Returns X").
Args:, Returns:, Raises: sections. Don't repeat type hints in the docstring. See the python rule for full details.
- CSS / Tailwind:
/* ... */. Comment the intent of token groups, not the value. Never comment individual utility classes; the class name is the doc. Long class strings (>10-12 utilities) signal an extraction, not a comment.
- SQL migrations: header comment block at the top (purpose, ticket, expand-contract phase if applicable). Inline
-- for non-obvious indexes, cascade choices, RLS predicates, partial-index predicates. Decorative section banners are tolerated in long migration files for readability.
- YAML / TOML / Dockerfile:
# comments. Comment non-default settings only (a non-default tracesSampleRate, a paths-ignore, a runner.environment gate). Don't comment image:, restart:, WORKDIR.
- HTML / Jinja:
<!-- --> for structural markers only. Use {# ... #} for developer notes in Jinja; <!-- --> ships to the browser. Never put secrets in HTML comments.
- JSON: no comments. Document the shape in the README or in a sibling
.md. JSON-with-comments (.jsonc) is the exception.
- Shell / bash:
#!/usr/bin/env bash then set -euo pipefail then a header comment block (purpose, required env vars, exit codes). Always comment any || true, 2>/dev/null, trap, or subshell construct. These are where bugs hide.
- Markdown:
<!-- --> sparingly (TOC markers, <!-- markdownlint-disable -->). Don't hide prose in HTML comments. Front-matter (---) is acceptable for tooling that consumes it.
TODO conventions
Format: <TAG>(<author>, <tracker-ID>): <description>.
TODO: known work to do.FIXME: bug to fix.HACK: deliberate workaround; explain why and what would let it go.XXX: warning to future readers (uncommon, reserve for genuine landmines).
The tracker ID is a Linear / Jira / GitHub issue number, not a date or a vague "later". A TODO without a tracker is a comment that will rot.
Disable / override directives
Always carry a reason:
// eslint-disable-next-line <rule> — name the specific rule, never bare.// @ts-expect-error <reason> — one-line justification, never bare.# type: ignore[code] — specific error code, never bare.# noqa: <rule> — specific ruff rule, never bare.
A bare disable directive is a code smell; the next reader has no way to know if it is still needed.
Smell test before committing a comment
- Does the code already say this? If yes, delete the comment.
- Could a better identifier eliminate the need? If yes, rename.
- Will the comment still be true in 6 months? If unsure, link a Linear / Jira / GitHub issue instead.
- Would a new contributor understand WHY from this comment alone? If yes, keep it.
- Did the comment narrate edit history rather than design intent? If yes, rewrite or delete.
- Does the comment cite a regulation, PPM section, treaty, or blueprint? If yes, verify the citation still applies before shipping.
If you cannot answer "yes" to question 4, the comment is probably dead weight.
Project overrides
A project's docs/commenting-standard.md (or equivalent) extends or overrides this baseline. If the project has stack-specific rules (TSDoc tag policy, Sphinx domain choice, Rustdoc style), follow those. This skill is the floor, not the ceiling.
