SkillCheck
Overview
Validate SKILL.md files against the agentskills specification and Anthropic best practices. Catches structural errors, semantic contradictions, naming anti-patterns, and quality gaps in a single read-only pass.
When to Use This Skill
- Use when user says "check skill", "skillcheck", or "validate SKILL.md"
- Use when reviewing a skill before publishing to a marketplace
- Use when debugging why a skill doesn't trigger correctly
- Use when onboarding a team to skill authoring standards
- Do NOT use for anti-slop detection, security scanning, or token analysis; use SkillCheck Pro for those
How It Works
Step 1: Parse
Read the target SKILL.md file and extract YAML frontmatter.
Step 2: Validate
Apply all Free tier checks in order:
| Category |
Checks |
What it catches |
| Structure (1.x) |
Name format, description WHAT+WHEN, allowed-tools, categories, XML injection |
Malformed frontmatter, missing fields |
| Body (2.x) |
Line count, hardcoded paths, stale dates, empty sections, deprecated syntax, MCP tool qualification |
Content quality issues |
| Naming (3.x) |
Vague terms, single-word names, gerund suggestions |
Poor discoverability |
| Semantic (4.x) |
Contradictions, ambiguous terms, missing output format, wisdom/platitudes, misplaced triggers |
Logical inconsistencies |
| Quality (8.x) |
Examples, error handling, triggers, output format, prerequisites, negative triggers |
Strengths (positive patterns) |
Step 3: Score
Calculate overall score (0-100). Penalties: critical = -20, warning = -5, suggestion = -1.
Step 4: Report
Return structured results: score, grade (Excellent/Good/Needs Work/Poor), issue list with check IDs, line numbers, messages, and fix suggestions.
Examples
Example 1: Validating a skill
User: check my skill at ~/.claude/skills/weekly-report/SKILL.md
SkillCheck output:
## weekly-report Check Results [FREE]
Score: 85/100 (Good)
### Warnings (2)
- 1.2-desc-when (line 3): Description missing WHEN clause
- 4.5-desc-no-triggers (line 3): Description lacks triggering conditions
### Suggestions (1)
- 3.4-gerund-naming (line 2): Skill name could use gerund form
### Passed Checks: 28
Example 2: Clean skill passes all checks
User: skillcheck ~/.claude/skills/processing-pdfs/SKILL.md
Score: 100/100 (Excellent)
All 31 checks passed. No issues found.
Limitations
- Read-only: does not modify any files
- Free tier covers structural, semantic, and naming checks only
- Anti-slop, security, WCAG, token, enterprise, and workflow checks require SkillCheck Pro
- Semantic checks (contradiction detection, wisdom/platitude) are heuristic with ~5% false positive rate
- Does not validate referenced files or scripts; only checks SKILL.md content
- Single-file validation; does not cross-check against other skills in the same directory
Best Practices
- Run SkillCheck before submitting skills to any marketplace
- Fix all critical and warning issues; suggestions are optional
- Use the check ID (e.g.,
1.2-desc-when) to find the exact rule in the skill body
- Re-run after fixes to confirm the score improved
Common Pitfalls
Problem: Score seems low due to many suggestions
Solution: Suggestions cap at -15 points total. Focus on warnings and criticals first.
Problem: False positive on ambiguous terms inside code blocks
Solution: SkillCheck skips code blocks and inline code. If you still see false positives, wrap the term in backticks.
Problem: Wisdom/platitude check flags legitimate instructions
Solution: Rephrase generic advice ("Remember that testing is important") as concrete directives ("Run tests before committing").
1---2name: skill-check3description: Validate Claude Code skills against the agentskills specification. Catches structural, semantic, and naming issues before users do.4license: MIT5---6# SkillCheck78## Overview910Validate SKILL.md files against the [agentskills specification](https://agentskills.io) and Anthropic best practices. Catches structural errors, semantic contradictions, naming anti-patterns, and quality gaps in a single read-only pass.1112## When to Use This Skill1314- Use when user says "check skill", "skillcheck", or "validate SKILL.md"15- Use when reviewing a skill before publishing to a marketplace16- Use when debugging why a skill doesn't trigger correctly17- Use when onboarding a team to skill authoring standards18- Do NOT use for anti-slop detection, security scanning, or token analysis; use [SkillCheck Pro](https://getskillcheck.com) for those1920## How It Works2122### Step 1: Parse2324Read the target SKILL.md file and extract YAML frontmatter.2526### Step 2: Validate2728Apply all Free tier checks in order:2930| Category | Checks | What it catches |31|----------|--------|----------------|32| Structure (1.x) | Name format, description WHAT+WHEN, allowed-tools, categories, XML injection | Malformed frontmatter, missing fields |33| Body (2.x) | Line count, hardcoded paths, stale dates, empty sections, deprecated syntax, MCP tool qualification | Content quality issues |34| Naming (3.x) | Vague terms, single-word names, gerund suggestions | Poor discoverability |35| Semantic (4.x) | Contradictions, ambiguous terms, missing output format, wisdom/platitudes, misplaced triggers | Logical inconsistencies |36| Quality (8.x) | Examples, error handling, triggers, output format, prerequisites, negative triggers | Strengths (positive patterns) |3738### Step 3: Score3940Calculate overall score (0-100). Penalties: critical = -20, warning = -5, suggestion = -1.4142### Step 4: Report4344Return structured results: score, grade (Excellent/Good/Needs Work/Poor), issue list with check IDs, line numbers, messages, and fix suggestions.4546## Examples4748### Example 1: Validating a skill4950```51User: check my skill at ~/.claude/skills/weekly-report/SKILL.md5253SkillCheck output:54## weekly-report Check Results [FREE]5556Score: 85/100 (Good)5758### Warnings (2)59 - 1.2-desc-when (line 3): Description missing WHEN clause60 - 4.5-desc-no-triggers (line 3): Description lacks triggering conditions6162### Suggestions (1)63 - 3.4-gerund-naming (line 2): Skill name could use gerund form6465### Passed Checks: 2866```6768### Example 2: Clean skill passes all checks6970```71User: skillcheck ~/.claude/skills/processing-pdfs/SKILL.md7273Score: 100/100 (Excellent)74All 31 checks passed. No issues found.75```7677## Limitations7879- Read-only: does not modify any files80- Free tier covers structural, semantic, and naming checks only81- Anti-slop, security, WCAG, token, enterprise, and workflow checks require [SkillCheck Pro](https://getskillcheck.com)82- Semantic checks (contradiction detection, wisdom/platitude) are heuristic with ~5% false positive rate83- Does not validate referenced files or scripts; only checks SKILL.md content84- Single-file validation; does not cross-check against other skills in the same directory8586## Best Practices8788- Run SkillCheck before submitting skills to any marketplace89- Fix all critical and warning issues; suggestions are optional90- Use the check ID (e.g., `1.2-desc-when`) to find the exact rule in the skill body91- Re-run after fixes to confirm the score improved9293## Common Pitfalls9495- **Problem:** Score seems low due to many suggestions96 **Solution:** Suggestions cap at -15 points total. Focus on warnings and criticals first.9798- **Problem:** False positive on ambiguous terms inside code blocks99 **Solution:** SkillCheck skips code blocks and inline code. If you still see false positives, wrap the term in backticks.100101- **Problem:** Wisdom/platitude check flags legitimate instructions102 **Solution:** Rephrase generic advice ("Remember that testing is important") as concrete directives ("Run tests before committing").
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