Relies on BDK foundation (STARTUP_INSTRUCTIONS.md). Assumes environment discovery has already run (language, test runner, build tool are known).

Skill Lint

Verify BDK skill or agent file meets portability and quality conventions.

Determine target

• $ARGUMENTS may be one or more space-separated paths.
• No arguments: ask user which file, or infer from recent context.

Per path:

1. Read file.
2. List all files in skill directory (recursively). Every file other than SKILL.md is supporting file.
3. Each supporting file: lint too (checks 3–6 only — portability checks), regardless of whether referenced in SKILL.md.

Print separate report block per file linted.

Run checks

Report each check as PASS, FAIL, or WARN with one-line reason.

1. Frontmatter present

• File must start with ---
• Must contain name: field
• Must contain description: field

2. Model field

• Agent files (agents/): model: required — FAIL if missing
• Skill files (skills/): model: recommended — WARN if missing (some skills intentionally inherit)

3. No absolute paths

Fail if file contains:

• /Users/, /home/, /root/, /opt/, /var/, C:\
• Any hardcoded filesystem path

4. No project-specific file references

Warn if file refs files only in one project:

• Patterns: specific filenames like src/foo.py, app/models/user.rb, internal/auth/handler.go
• Exception: generic illustrative examples (e.g. <your-file>, path/to/file)

5. No project-specific instructions

Warn if file contains phrases tied to specific project:

• "in this project", "this repo", "our codebase", specific org/team names
• Hardcoded branch names, database names, service names

6. No language-specific commands

Fail if file hardcodes language/framework tooling:

• Test runners: pytest, go test, npm test, yarn test, cargo test, rspec, jest, mocha
• Build tools: mvn, gradle, cargo build, make (as build command)
• Linters: ruff, eslint, golangci-lint, rubocop, flake8

Use generic phrasing: "run the project's test suite", "run the linter".

7. BDK foundation header (skills only)

Skills must start body (after frontmatter) with:

> Relies on BDK foundation (STARTUP_INSTRUCTIONS.md)...

FAIL if missing.

8. Skill cross-references use full namespace

Refs to other BDK skills must use /bdk: prefix.

• FAIL on: /commit, /debug, /create-plan (bare names)
• PASS on: /bdk:commit, /bdk:debug

9. name format valid

If name: present: must match ^[a-z0-9-]{1,64}$.

• FAIL on uppercase, underscores, spaces, or >64 chars.

10. description length

If description: present: WARN if >250 chars (truncated in skill listing).

11. Invalid frontmatter fields

FAIL if file uses unsupported/obsolete frontmatter fields:

• arguments: (list of objects) — replaced by argument-hint:
• Any field not in: name, description, argument-hint, disable-model-invocation, user-invocable, allowed-tools, disallowed-tools, model, effort, context, agent, background, hooks, paths, shell

12. effort valid value

If effort: present: must be one of low, medium, high, xhigh, max.

• FAIL on any other value.

13. context + agent combo

If agent: present but context: fork missing: WARN — agent: only applies with context: fork.

14. Dead skill combo

If both disable-model-invocation: true AND user-invocable: false: FAIL — skill inaccessible.

15. $ARGUMENT typo

If body uses $ARGUMENT (no S): FAIL — correct variable is $ARGUMENTS or $ARGUMENTS[N].

16. External skill/agent references

BDK skills depend only on BDK-owned skills. Flag /slash-command and agent name invocations NOT prefixed /bdk:.

Slash command refs (/name in body):

• WARN on bare /name refs (e.g. /commit, /debug) — ambiguous, may resolve to wrong skill
• WARN on /other-plugin:name — hard dep on external plugin not guaranteed present
• PASS on /bdk:name — BDK namespace, expected

Agent refs (backtick or plain agent-name in body, e.g. `test-runner`):

1. Check if agents/<name>.md exists in BDK repo.
2. If exists → WARN: bare name found, use /bdk:<name> prefix.
3. If not exists → WARN: unknown agent dependency, not shipped with BDK.

17. Skill directory format

Per Claude Code skills spec, each skill must live at <skill-name>/SKILL.md.

• FAIL if filename not exactly SKILL.md (case-sensitive)
• WARN if parent dir name doesn't match name field in frontmatter (causes confusing dual identities)

18. Artifacts go to .bdk/

Skills producing file output must write to .bdk/ in project root, not arbitrary dirs.

• FAIL if skill body instructs writing to docs/, output/, tmp/, reports/, or other non-.bdk paths
• PASS if output path is .bdk/... or no file output produced
• Exception: skills writing code/config into project structure as part of code-gen task (not report/artifact output)

19. No unused files in skill directory

List all files in skill directory (recursively). Every file other than SKILL.md must be referenced in skill body (markdown link, inline code mention, or explicit filename reference).

• WARN for each file present but not referenced anywhere in SKILL.md
• Exception: SKILL.md itself always exempt

Check: list dir contents, scan SKILL.md body for each filename. Not found → WARN.

20. Valid skill directory structure

Allowed layout:

<skill-name>/
├── SKILL.md            ← required, exactly this name
├── references/
│   └── *.md            ← templates and reference docs
├── examples/
│   └── *.md            ← example output files only
├── scripts/
│   └── *               ← executable scripts only (*.sh, *.py, etc.)
└── fragments/
    └── *.md            ← conditional injection targets

Rules:

• FAIL if any subdirectory other than examples/, references/, scripts/, or fragments/ exists
• WARN if fragments/ contains non-.md files
• WARN if *.md template/reference files sit at root level instead of references/ — suggest moving
• WARN if examples/ contains non-.md files
• WARN if references/ contains non-.md files
• WARN if scripts/ contains non-script files (non-executable or non-.sh/.py/.js/.rb extensions)
• WARN if any file at root level that is not SKILL.md (e.g. .sh scripts at root → scripts/, .md files → references/)
• PASS if only SKILL.md present (minimal valid structure)

21. Inject conditions use a recognised form

For every !...inject.py ...`` call in the body, check each --if / --prefer condition against the three forms scripts/inject.py actually parses:

• FAIL on anything else (e.g. languages.react, feature.react, tool[lavish-axi]) — name the line and the correct spelling.
• The two near-misses matter most because they fail silently: languages.react matches no regex and raises, while tool[lavish-axi] is happily parsed by the array rule as a lookup in a nonexistent tool list and evaluates false forever. Neither looks broken in the rendered skill.
• Also FAIL a --then path that does not exist, for the same reason: a missing fragment renders as an absent one.

22. Stated tool invariants are enforced

allowed-tools is pre-approval, not a whitelist: listing tools there restricts nothing. When a skill's body states that it must never call a tool, the restriction belongs in disallowed-tools, which removes the tool from the pool.

WARN when the body asserts such an invariant and the frontmatter does not back it:

Name the body line and the missing field. Do not FAIL: a skill may legitimately need the tool on some path, and the field cannot express "only for X". PASS when the invariant is absent or already backed.

Output format

One report block per file. Supporting files get abbreviated reports (checks 3–6 only).

SKILL LINT: skills/brainstorming/SKILL.md
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
PASS  Frontmatter present (name, description)
FAIL  No model defined — agent files require model:
PASS  No absolute paths
WARN  Project-specific reference: src/auth/middleware.py (line 14)
PASS  No project-specific instructions
FAIL  Language-specific command: pytest (line 22) — use "run the project's test suite"
PASS  BDK foundation header present
PASS  Skill references use /bdk: namespace
PASS  name format valid
PASS  description length OK
PASS  No invalid frontmatter fields
PASS  Directory format correct (SKILL.md, dir matches name)
WARN  External skill reference: /deploy (line 44) — use /bdk: prefix or remove dependency
FAIL  Artifact path: docs/designs/ (line 88) — skills must write artifacts to .bdk/
WARN  Unused file: examples/old-sample.md — not referenced in SKILL.md
PASS  Directory structure valid (SKILL.md, examples/, scripts/)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
2 failures, 2 warnings

SKILL LINT: skills/brainstorming/reference.md  [supporting file — portability checks only]
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
PASS  No absolute paths
PASS  No project-specific file references
PASS  No project-specific instructions
PASS  No language-specific commands
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
All checks passed.

All files pass → end with: All checks passed.

No fixes beyond check results unless user asks.

Checklist before responding

Verify ALL 21 checks were executed for SKILL.md (not just the ones that seemed relevant):

• 1. Frontmatter present
• 2. Model field
• 3. No absolute paths
• 4. No project-specific file references
• 5. No project-specific instructions
• 6. No language-specific commands
• 7. BDK foundation header
• 8. Skill cross-references use full namespace
• 9. name format valid
• 10. description length
• 11. Invalid frontmatter fields
• 12. effort valid value
• 13. context + agent combo
• 14. Dead skill combo
• 15. $ARGUMENT typo
• 16. External skill/agent references
• 17. Skill directory format
• 18. Artifacts go to .bdk/
• 19. No unused files in skill directory
• 20. Valid skill directory structure
• 21. Inject conditions use a recognised form

Do not output the checklist. Use it internally to confirm no check was skipped.