Skillcheck

skillcheck is a static analyzer for SKILL.md files. It validates frontmatter structure, scores description discoverability, checks file references, and extracts a capability graph from heading and backtick-reference patterns. Run it before committing a skill, plugging it into CI, or publishing to a skill registry.

Prerequisites

• path - the SKILL.md file or directory to validate
• prompt.txt - file path for a saved agent prompt (critique or graph extraction)
• response.json - file path for an agent-provided JSON response

Validate a skill

Pass path to skillcheck for a full structural check against the agentskills.io specification. Validates name constraints, description quality, body sizing, file references, and cross-agent compatibility. The validation report is written to stdout. Exit codes: 0 no errors, 1 errors found, 2 input error (missing file), 3 symbolic passed but semantic critique flagged errors.

skillcheck 
skillcheck  --format json

Review a skill with an agent

skillcheck generates a structured critique prompt for path and ingests response.json as the agent's reply. Save the emitted prompt to prompt.txt. The merged validation report combines symbolic diagnostics and semantic findings from the critique.

skillcheck  --emit-critique-prompt > prompt.txt

Hand prompt.txt to your agent. The agent returns JSON. Save the response as response.json, then ingest it.

skillcheck  --ingest-critique response.json

Pass --critique-agent codex or --critique-agent cursor to select a prompt variant tuned for that platform. The critique JSON schema is identical across all agent targets.

Extract a capability graph

skillcheck extracts the capability graph from heading structure and backtick references in the body of path. Use prompt.txt for emitted graph prompts and ingest response.json from your agent for richer extraction.

Run graph analysis using the heuristic extractor (no agent needed):

skillcheck  --analyze-graph

For richer extraction, emit the graph prompt, run it through your agent, and ingest the response:

skillcheck  --emit-graph-prompt > prompt.txt
skillcheck  --ingest-graph response.json

Print the graph to stdout:

skillcheck  --emit-graph
skillcheck  --emit-graph --format json

When both heuristic and agent graphs are available, skillcheck compares them and emits graph.contradiction.heuristic_disagreement at error severity for agent-claimed edges that the heuristic does not confirm.

Check validation history

Append a record to the validation ledger for each --history run on path. The ledger is stored in .skillcheck-history.json next to the skill file, is append-only, and is safe to commit.

skillcheck  --history
skillcheck  --show-history
skillcheck  --show-history --format json

Each record stores the timestamp, skillcheck version, a 16-character content hash, which validation modes ran, and diagnostic counts. When the skill content matches a prior passing run but the current run fails, skillcheck emits history.skill.regressed to flag rule tightening or a new agent finding.

Outputs

• validation report - diagnostic output written to stdout
• capability graph - graph of capabilities, inputs, and outputs extracted from the skill body
• validation ledger - written to .skillcheck-history.json next to the skill file

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: moonrunnerkc
• Source: moonrunnerkc/skillcheck
• License: MIT

Install and usage instructions live in the source repository linked above.