agents-md

Repository-scoped hygiene for AGENTS.md: create it, measure it, audit its content, and check it against its harness mirrors. One canonical file, harness-neutral, no frontmatter.

.github/copilot-instructions.md authoring and Copilot code-review setup live in /github-copilot-repo-instructions (if installed). This skill only checks that file's mirror status against AGENTS.md; it does not write Copilot-specific content or applyTo path rules.

Personal or machine-global instruction files (a user's own ~/.claude/CLAUDE.md, personal Copilot instructions) are out of scope. This skill only touches files committed to the repository.

Why AGENTS.md hygiene matters

AGENTS.md is a vendor-neutral, plain-Markdown convention with no required fields (agents.md). Every major harness loads the file in full on every turn, so its length is a per-run token cost, not a one-time readability cost. A stale command or a bloated file taxes every future turn.

Effectiveness evidence is mixed: keep the file for the token-cost and precedence reasons above, not on a promise of a guaranteed task-success lift. See references/harness-matrix.md for the sourced detail.

Protocol

1. Inventory instruction files

List what exists, repository-relative, root and nested:

find . -maxdepth 4 \( -name AGENTS.md -o -name CLAUDE.md -o -name CLAUDE.local.md \
  -o -name GEMINI.md -o -path '*/.github/copilot-instructions.md' -o -path '*/.cursor/rules*' \) \
  -not -path '*/node_modules/*'

Each harness reads a different subset with different precedence and caps. Read references/harness-matrix.md before assuming one file's presence or absence is equivalent to another's — nearest-file precedence is the norm (agents.md spec, Codex, Copilot, Cursor), but Claude Code's own trigger is different: it reads AGENTS.md only when no CLAUDE.md/CLAUDE.local.md exists above the working file, or via an explicit @AGENTS.md import inside a CLAUDE.md.

2. Measure

python3 "$AGENTS_MD_CHECK" [path/to/AGENTS.md]

Resolve AGENTS_MD_CHECK from the loaded SKILL.md directory (scripts/agents_md_check.py), resolving symlinks first. Do not assume the skill sits at skills/agents-md/ in the target repository.

Reports bytes, lines, the heading map, every referenced just <recipe> checked against a nearby justfile, every referenced repo-relative path, and the mirror status of CLAUDE.md, .github/copilot-instructions.md, and GEMINI.md. Flag a file over ~200 lines as a soft readability warning. The script also sums the AGENTS.md chain from the repository root to each directory at or below the checked file. A chain over 32 KiB fails outright. OpenAI Codex concatenates that chain from the root down. It stops adding files when the combined size reaches project_doc_max_bytes (32 KiB by default), so the files nearest the working directory drop first (https://developers.openai.com/codex/guides/agents-md/).

Root discovery and skip rules follow Codex:

• The root is the nearest directory at or above the checked file that contains .git. With no .git, each chain is the checked file only, and the report says "file directory" instead of "repository root".
• Per directory, AGENTS.override.md counts when present, else AGENTS.md.
• Sizes are raw on-disk bytes, so CRLF line endings count in full.
• The walk skips dot directories, node_modules, broken symlinks, and any subdirectory with its own .git (a nested project root).

Exit codes: 0 when no chain breaches the cap, no mirror has diverged, and every referenced recipe and path exists. 1 on a cap breach, on any drift (diverged mirror, missing recipe, or missing path), or when the file does not exist.

--json prints these fields: path, bytes, chain_bytes, chain_dir (the deepest directory of the largest chain, relative to the root), root_marker (true when a .git root was found), lines, byte_cap, cap_breach, near_cap, line_warn, headings, justfile, referenced_just_recipes, missing_recipes, referenced_paths, missing_paths, mirrors, diverged_mirrors, and drift.

3. Content audit

For every command and path AGENTS.md names, verify it against the real repository, not against memory:

• Every backticked just <recipe> exists in the justfile — the script checks this; treat a FAIL missing just recipes line as a stale command, not a script bug.
• Every backticked repo-relative path exists — same treatment for FAIL missing referenced paths.
• Quality gates, conventions, and "do not touch" boundaries match the project's actual CI and review practice, not an aspirational one.
• PR and commit rules are stated, not implied.

Anti-patterns to flag and remove, per references/content-checklist.md: narrative history, README duplication, secrets or tokens, per-person preferences, and any command that no longer runs.

4. Mirror strategy

Keep exactly one canonical AGENTS.md. For each mirror:

• CLAUDE.md: either absent, or contains only @AGENTS.md (a Claude Code import — https://code.claude.com/docs/en/memory). Do not duplicate content into it.
• .github/copilot-instructions.md: either absent (Copilot reads AGENTS.md directly) or a short pointer. If the user wants Copilot-specific content (path-scoped applyTo rules, code-review knobs), route to /github-copilot-repo-instructions — do not author that file here.
• GEMINI.md: either absent or a short pointer, same pattern as CLAUDE.md.

Report any mirror the check script marks diverged as drift, and propose collapsing it to a pointer or removing it.

5. Nested AGENTS.md

For a monorepo or multi-package layout, put a nested AGENTS.md in each package that needs its own rules. Codex, Claude Code, Cursor, Gemini CLI, and Copilot CLI load the nested file together with every ancestor file. No harness replaces the root file with the nested file. The nearer file wins only on conflict. See references/harness-matrix.md for each harness.

• Put only the subtree's delta in the nested file: its own commands, boundaries, and exceptions. A copied root rule loads twice on every turn and drifts.
• State each exception to a root rule explicitly, and name the root rule that it replaces. VS Code warns that harnesses do not share one precedence order.
• Keep every root-to-leaf chain under the Codex 32 KiB cap. Codex drops the nearest files first.
• Claude Code reads a nested AGENTS.md only when that directory has no CLAUDE.md of its own.

6. Trim or rewrite

Always show the proposed change as a diff against the current file. Then stop and ask for explicit approval before writing AGENTS.md or any mirror. A request to skip the diff ("I don't need to see the diff") does not waive this step and is not approval. Write only after the user approves the diff that you showed.

Never run git commit or git push. Leave the changes in the working tree. The user owns commits.

Use assets/AGENTS.md.template as the starting shape for a new file, not as boilerplate to paste unedited — every section must reflect this repository's actual commands and boundaries.

7. Verify

python3 "$AGENTS_MD_CHECK" --self-test
python3 "$AGENTS_MD_CHECK"

Both must exit 0. Re-run any command the audit changed or added before reporting done.

Rules

• One canonical AGENTS.md per directory scope. Mirrors point at it; they do not restate it.
• Never invent a command or path. Every backticked just <recipe> and every referenced path must exist — the check script verifies this, do not skip it.
• Do not add narrative, README duplication, secrets, or per-person preferences. See references/content-checklist.md for the full list.
• Do not write .github/copilot-instructions.md content beyond a short pointer — that authoring belongs to /github-copilot-repo-instructions.
• Do not touch personal or machine-global instruction files.
• Show the diff and get explicit approval before overwriting an existing AGENTS.md or mirror. A request to skip the diff is not approval.
• Never run git commit, git push, or any other publication command. Leave changes in the working tree.

References

• references/harness-matrix.md — which harness reads which file, with precedence and size caps, cited.
• references/content-checklist.md — what belongs in AGENTS.md and what does not. Harness-behavior claims are cited; the lists are this skill's guidance.
• assets/AGENTS.md.template — a short, sectioned starting template.