SKILL.md validator
Check a skill against the spec, then against five real runtimes.
Paste your SKILL.md, or drop the file. Structural checks run against the specification’s own field constraints; portability checks run against what’s documented for Claude Code, Codex, Cursor, OpenClaw, and Hermes Agent. Nothing you paste leaves the browser — there’s no upload, no model call, and no result URL.
The standard ships its own reference validator, skills-ref validate, which checks the format. This adds what that doesn’t: per-runtime portability against documented behaviour for five runtimes, and heuristic signals on whether the description reads as a trigger condition. See every rule this checker knows about at the rule reference.
Pasted text has no filename or folder — drop the file instead to check those too.
Where this checker's rules come from
- SKILL.md, the formatEvery frontmatter field and its real constraints, and where five runtime implementations diverge from the spec.
- Agent Skills Not WorkingThe diagnostic reference this checker's portability rules are drawn from, including the verified issues cited by number.
- Agent Skills CompatibilityWhat travels between runtimes, with explicit evidence levels for each claim.
- The rule referenceEvery check this validator runs, as its own page — what it is, where it comes from, and how to fix it.