SkillCheck Free
Validate AI coding assistant skills against the agentskills specification. Works with Claude Code, Claude Desktop/Web, and Cursor. Catch issues before your users do.
Why SkillCheck?
Agent Skills are now an open standard adopted by Claude Code, Cursor, and dozens of coding agents. Your skill needs to work everywhere and follow best practices.
SkillCheck validates:
- Does the YAML frontmatter follow the spec?
- Will it trigger when users actually need it?
- Are the instructions clear and unambiguous?
Installation
Claude Code
The simplest path — use the skills CLI:
npx skills add olgasafonova/SkillCheck-Free
Or copy the folder manually:
cp -r skills/skill-check ~/.claude/skills/
Or clone directly:
git clone https://github.com/olgasafonova/SkillCheck-Free.git
cp -r SkillCheck-Free/skills/skill-check ~/.claude/skills/
Claude Desktop/Web (Projects)
- Open claude.ai or Claude Desktop app
- Create a new Project (or open an existing one)
- Go to Project settings → Custom instructions
- Copy the contents of
skills/skill-check/SKILL.md(everything after the---frontmatter) - Paste into the custom instructions field
No file installation needed - the skill runs directly from your Project instructions.
Cursor
Copy the rule file to your project's .cursor/rules directory:
mkdir -p .cursor/rules
cp cursor-rules/skill-check.mdc .cursor/rules/
Or clone directly:
git clone https://github.com/olgasafonova/SkillCheck-Free.git
mkdir -p .cursor/rules
cp SkillCheck-Free/cursor-rules/skill-check.mdc .cursor/rules/
Where to find SkillCheck-Free
SkillCheck-Free is listed in:
- skills.sh registry — install via
npx skills add olgasafonova/SkillCheck-Free - antigravity-awesome-skills — included in sickn33's 1,239+ universal agentic skills collection
Usage
In Claude Code, Claude Desktop/Web, or Cursor, say any of:
- "skillcheck my skill"
- "check skill at path/to/SKILL.md"
- "validate my skills"
Example Output
## SkillCheck Results: my-awesome-skill
### Summary
- Critical: 1 | Warnings: 2 | Suggestions: 3 | Passed: 44
### Critical Issues
**[1.2-desc-what]** Line 3: Description missing action verb
**Fix**: Start description with Create, Generate, Build, Convert, etc.
### Warnings
**[4.2-ambiguous-term]** Line 47: Vague term "several" found
**Fix**: Specify exact count or range
### Strengths
- Skill includes example section
- Skill documents prerequisites
- Description includes activation triggers
What It Checks
Structure (1.x)
| Check | What It Catches |
|---|---|
| 1.1-name | Invalid name format, reserved words |
| 1.2-desc | Missing or weak description (WHAT verb + WHEN trigger recommended) |
| 1.3-tools | Unknown or deprecated tool formats |
| 1.4-category | Invalid category format |
| 1.9-xml | XML angle brackets in frontmatter (prompt injection risk) |
| 1.9-arg-hints | Missing argument-hint in frontmatter when $ARGUMENTS is used |
| 1.10-readme | README.md inside skill folder (docs belong in SKILL.md) |
Body (2.x)
| Check | What It Catches |
|---|---|
| 2.1-lines | File too long (500+ lines warning) |
| 2.3-date | Hardcoded dates that will go stale |
| 2.4-empty | Empty sections with no content |
| 2.8-antipattern-format | Anti-pattern sections using prose instead of tables/bullets |
| 2.9-mcp-tool-unqualified | Unqualified MCP tool names missing server prefix |
Naming (3.x)
| Check | What It Catches |
|---|---|
| 3.1-vague | Generic names like "helper", "utils" |
| 3.2-length | Names too short or too long |
| 3.3-single | Single-word names lacking specificity |
| 3.4-gerund | Gerund naming ("writing-helper" instead of verb-noun) |
Semantic (4.x)
| Check | What It Catches |
|---|---|
| 4.1-contradiction | Conflicting instructions |
| 4.2-ambiguous | Vague terms like "several", "appropriate" |
| 4.3-output | Output mentioned but no format specified |
| 4.6-wisdom | Generic advice/platitudes instead of actionable instructions |
| 4.7-desc-workflow-steps | Description summarizes workflow steps (causes agents to skip body) |
Design Pattern Classification (19.x)
SkillCheck classifies each skill into one of five design patterns from the Google ADK taxonomy:
| Pattern | What It Means | Example Skills |
|---|---|---|
| Reviewer | Evaluates output against criteria | skill-check, code-review |
| Generator | Produces structured artifacts from templates | linkedin-post, brand-assets |
| Inversion | Asks user questions before acting | grill-me, feature-scoping |
| Pipeline | Chains multiple steps with checkpoints | sift, tapestry |
| Tool Wrapper | Wraps an API with context-aware instructions | lmwtfy |
Pro adds deep checks: validates pattern-specific requirements (criteria for Reviewers, output specs for Generators, etc.).
Quality Patterns (8.x) - Strengths
SkillCheck also recognizes good practices:
| Check | What It Recognizes |
|---|---|
| 8.1 | Has example section |
| 8.2 | Documents error handling or limitations |
| 8.3 | Description includes activation triggers |
| 8.4 | Specifies output format with examples |
| 8.5 | Uses structured instructions (numbered steps) |
| 8.6 | Documents prerequisites |
| 8.7 | Includes negative triggers to prevent over-triggering |
| 8.8 | Uses ${CLAUDE_SKILL_DIR} for portable path references |
Knowledge Density (22.x)
| Check | What It Catches |
|---|---|
| 22.7 | Gotchas/troubleshooting sections with only generic filler and no concrete knowledge |
Pro adds: threshold detection (22.1), consequence patterns (22.2), experience markers (22.3), debugging sequences (22.4), decision density (22.5), and concrete code references (22.6).
Plugin Manifest (24.x)
When the input is a Claude Code plugin manifest (.claude-plugin/plugin.json), SkillCheck Free validates it against Anthropic's reference schema:
| Check | What It Catches |
|---|---|
| 24.1 | name not in kebab-case |
| 24.2 | version not canonical semver (no v prefix, must be MAJOR.MINOR.PATCH) |
| 24.3 | description missing or empty |
| 24.4 | author.name missing or empty |
| 24.5 | Command file collides with bundled Claude Code commands (simplify, batch, debug, loop, claude-api, security-review) |
| 24.6 | .claude-plugin/ contains files other than plugin.json (commands/skills/hooks belong at plugin root) |
Schema-floor rule: any rule that rejects Anthropic's own reference plugins is mis-calibrated. Validation stays compatible with the four-field minimum.
Pro adds Cat 24 marketplace governance: cross-plugin dedup detection, naming convention enforcement against an org taxonomy, change-gate eval integration, maintainers and deprecation provenance recommendations, and cross-skill dependency graphs.
MCP Tool List (23.x, Free hook)
When the input is an MCP server's tools/list response (standard MCP shape), SkillCheck Free surfaces two Agent Integration Readiness signals:
| Check | What It Catches |
|---|---|
| 23.1-tool-count-high | Server exposes >20 tools (consider intent grouping or code-orchestration) |
| 23.1-tool-count-strong | Server exposes >40 tools (strong code-orchestration candidate, Cloudflare 2-tool reference) |
| 23.1-api-mirror | 3+ CRUD verb prefixes against the same noun (1:1 OpenAPI mirror smell) |
Pro adds full Cat 23: CIMD-OAuth detection, MCP Apps usage, code-orchestration adoption, server-delivered skills pairing, remote vs local availability, destructive flag annotations, and user-vs-agent distinction enforcement.
OWASP Agentic Top 10 (26.x)
Maps the OWASP Top 10 for Agentic Applications (2026) onto author-time text signals. The category only scores a skill with an agent surface (declares tools beyond Read/Glob/Grep, ingests external content, orchestrates subagents, or performs consequential actions); a plain text-formatting skill reports not-applicable. SkillCheck Free runs the 8 items with a deterministic signal:
| Check | What It Catches |
|---|---|
| ASI-02 Tool Misuse | allowed-tools: */all (critical), unconstrained Bash, or 5+ tools with no rationale |
| ASI-03 Identity Abuse | caller-identity-override params (as_user, impersonate, run_as, etc.) |
| ASI-04 Supply Chain | unpinned dependency installs (pip install x, npm install x, npx x@latest) |
| ASI-05 Code Execution | eval/exec/pickle.loads/subprocess shell=True or curl ... | sh |
| ASI-08 Cascading Failure | uncapped loops or fan-out ("retry until", "loop until") |
| ASI-09 Trust Exploitation | destructive op (rm -rf, git push --force, send/merge) with no confirmation gate nearby |
| ASI-10 Rogue Agents | safeguard-disabling flags (--no-verify, --force) or long-running tasks with no kill switch |
| ASI-11 Untraceability | consequential actions with zero logging/audit language |
Pro adds the 7 grader items (ASI-01 goal hijack, ASI-06 memory poisoning, ASI-07 subagent trust, and the intent-reading halves of ASI-02/03/09/10): SkillCheck builds an evidence-loaded rubric pack and your own AI agent judges it, with no API key needed.
Severity Levels
| Level | Meaning | Action |
|---|---|---|
| Critical | Skill may not function | Must fix |
| Warning | Best practice violation | Should fix |
| Suggestion | Could be improved | Nice to have |
| Strength | Good practice detected | Keep it up |
Free vs Pro
| Feature | Free | Pro |
|---|---|---|
| Structure validation | Yes | Yes |
| Body & naming checks | Yes | Yes |
| Semantic consistency | Yes | Yes |
| Quality patterns | Yes | Yes |
| Design Pattern Classification | Detection | Deep checks |
| Knowledge Density | Hollow content | Full density analysis |
| OWASP Agentic Top 10 | 8 deterministic checks | Grader pack your AI evaluates |
| Artifact Contract Validation | - | Yes |
| Trigger Collision Detection | - | Yes |
| Eval Kit (test prompt generation) | - | Yes |
| Anti-slop detection | - | Yes |
| Security scanning | - | Yes |
| Token budget analysis | - | Yes |
| WCAG accessibility | - | Yes |
| Enterprise readiness | - | Yes |
| Production readiness | - | Yes |
| Agent Readiness (L0-L3) | - | Yes |
| MCP server integration | - | Yes |
| CI/CD binary | - | Yes |
Get Pro: getskillcheck.com
Prerequisites
- Claude Code (or any AI assistant with file Read capability)
- Works on macOS, Linux, Windows
- No dependencies required
How It Works
SkillCheck Free is itself a skill/rule file. When you say "skillcheck", your AI assistant reads the validation rules and applies them to your target skill. No external API calls, no binaries - just your assistant following instructions.
Contributing
Found a bug or have a suggestion? Open an issue at github.com/olgasafonova/SkillCheck-Free/issues
Links
- Website: getskillcheck.com
- Specification: agentskills.io
- Pro version: SkillCheck Pro
License
MIT - see LICENSE
Built by Olga Safonova