/skill-check

name: skill-check
description: Validate skill/command file format and structure. Use after creating or editing a skill, before committing skill changes, or when a skill fails to load or trigger.
user-invocable: true

Skill File Validator

Validate skill files for correct format against the official Claude Code spec.

---

Validation Target

• With argument: validate specific file
• Without: validate all `.claude/skills/*/SKILL.md`

---

Frontmatter Reference (official fields)

Skills support these fields. Only `description` is meaningfully required (a skill with none of these still loads — `name` defaults to the directory name).

---
name: skill-name              # Optional: defaults to directory name; lowercase, hyphenated
description: What it does      # Recommended: shown in / menu and used for triggering
when_to_use: When to reach for it  # Optional: appended to description for triggering
                              #   (description + when_to_use truncated at 1,536 chars in listings)
user-invocable: true          # Optional: default true; false hides from / menu (Skill tool still works)
model: sonnet                 # Optional: fable, opus, sonnet, haiku, inherit, default, best,
                              #   sonnet[1m], opus[1m] (or a full model ID). NOT opusplan (session-only)
effort: medium                # Optional: low, medium, high, xhigh, max
allowed-tools:                # Optional: pre-approved tools. Accepts a comma-separated string
  - Read                      #   OR a YAML list — BOTH are official (list shown here as house style)
  - Grep
  - Glob
disallowed-tools:             # Optional: explicitly blocked tools (string or YAML list)
  - WebFetch
context: fork                 # Optional: run the skill in a subagent
agent: agent-name             # Optional: subagent type when context: fork (default: general-purpose)
argument-hint: "[issue-number]"  # Optional: autocomplete hint shown after the skill name
arguments: target flags       # Optional: space-separated argument NAMES for $name substitution
                              #   (e.g. arguments "target flags" -> use $target and $flags in the body).
                              #   NOT a structured array of name/description/required objects.
disable-model-invocation: false  # Optional: bool; true also blocks scheduled-task invocation
paths:                        # Optional: glob patterns that limit where the skill activates
  - "src/**/*.ts"
shell: bash                   # Optional: bash or powershell for inline !`command` blocks
hooks:                        # Optional: skill-scoped lifecycle hooks (same schema as settings.json)
  PreToolUse:
    - matcher: Write
      hooks:
        - type: command
          command: ./scripts/validate.sh
  Stop:
    - hooks:
        - type: command
          command: ./scripts/verify.sh
          once: true
---

Valid Tools (for allowed-tools / disallowed-tools)

Read, Write, Edit, Bash, Grep, Glob, Agent (Task = legacy alias),
Skill, WebFetch, WebSearch, TodoWrite, NotebookEdit, AskUserQuestion

Non-official fields (flag as warnings, not errors)

metadata, license, version   # Not part of the skill spec; harmless but should be removed
once                         # Valid ONLY inside a hooks[] entry, never at skill top level

---

Validation Checklist

Required / Recommended Fields

• [ ] `description` present (recommended; used for the / menu and triggering)
• [ ] `name`, if present, is lowercase and hyphenated (defaults to directory name if omitted)

Optional Field Validation

• [ ] `allowed-tools` / `disallowed-tools` are valid tool names
• [ ] `allowed-tools` / `disallowed-tools` are a comma-separated string OR a YAML list (both valid)
• [ ] `allowed-tools` does not broadly preapprove bare `Bash`, `Edit`, `Write`, `Agent`, `Task`, or `Skill`; omit it when normal runtime approval is required
• [ ] `model` is a valid value: fable, opus, sonnet, haiku, inherit, default, best, sonnet[1m], opus[1m], or a full model ID (NOT opusplan)
• [ ] `effort` is one of: low, medium, high, xhigh, max
• [ ] `context` is `fork` (if specified)
• [ ] `agent` only set alongside `context: fork` (defaults to general-purpose)
• [ ] `argument-hint` is a string
• [ ] `arguments` is a space-separated string of argument names (NOT a structured array)
• [ ] `when_to_use` is a descriptive string (appended to description for triggering)
• [ ] `disable-model-invocation` is boolean
• [ ] `paths` is a list of glob patterns
• [ ] `shell` is `bash` or `powershell`
• [ ] `user-invocable` is boolean
• [ ] `hooks` has valid structure (matcher + hooks[] with type/command)

Unknown / Non-official Fields

• [ ] Warn (do not error) on `metadata`, `license`, `version`
• [ ] Warn on `once` used at the top level (only valid inside a hooks[] entry)

Content Structure

• [ ] Clear instructions
• [ ] Uses `$ARGUMENTS` (or `$name` per `arguments`) if expecting input
• [ ] Step-by-step process if complex

---

Output Format

## Skill Validation Report

### Files Checked
| File | Status | Issues |
|------|--------|--------|
| workflow/SKILL.md | OK | None |
| my-skill/SKILL.md | WARN | Missing description |

### Summary
- Total: [N]
- Valid: [N]
- Needs fixes: [N]

---

Auto-Fix

• Add missing `name` from directory name
• Add missing `description`
• Normalize a comma-separated `allowed-tools` string to a YAML list (house style only — the string form is valid; do NOT flag it as an error)
• Remove non-official fields (`metadata`, `license`, `version`)
• Convert a structured `arguments` array to a space-separated name string
• Replace `opusplan` model with a supported value
• Add `$ARGUMENTS` handling