SKILL.md Validator
Paste a SKILL.md (or drop the file) and get an instant, line-by-line check against the agent skills spec — the same rules our ingestion pipeline enforces before a skill can be listed. Private: it all runs in your browser.
Validator FAQ
What does SKILL.md need to be valid?
The file must start with YAML frontmatter (--- delimiters) containing a name and a description. The name is lowercase letters, numbers and hyphens, max 64 characters. The description is max 1024 characters, written in third person, and should state what the skill does and when to use it. The body should open with a level-1 heading.
Why does my SKILL.md fail with “must start with YAML frontmatter”?
Almost always a stray blank line or comment above the first --- line, or a missing closing --- delimiter. The validator pinpoints which one it is — paste your file to see.
Does the validator upload my file anywhere?
No. Validation runs entirely in your browser. Nothing is sent to a server, logged, or stored.
How long should a SKILL.md be?
Lean. Under ~500 lines, ideally under 150. The standard's pattern is progressive disclosure: SKILL.md carries the procedure, extra detail lives in references/*.md files and runnable code in scripts/, so the agent loads them only when needed.
From valid to verified
A clean validator pass means your skill is well-formed. The directory goes further: every submission is pinned to a commit, license-classified, security-scanned and benchmarked with and without the skill before it earns a listing — see the methodology. Pass the checks? Submit it. Need a skill from scratch? Try the skill builder.