An agent decides whether to use a skill from two lines of frontmatter. Skill Check reads your SKILL.md the way an installer does and lists what would stop it loading or triggering. Free, no sign-up, and your file never leaves your browser.
Six well-known public skill collections, checked on 13 November 2026. A failure means the file breaks the Agent Skills format. A warning is a judgement call, and we say which below.
Each SKILL.md was run through the same code as the checker above, at these commits: anthropics/skills 2c5958e (20 skills), obra/superpowers 22f0b46 (15), vercel-labs/agent-skills 1a2c79d (9), wshobson/agents 9c61ab2 (185), K-Dense-AI/claude-scientific-skills 2d2065f (177) and ComposioHQ/awesome-claude-skills be2a406 (864).
The same checks as check_skill.py, the open validator inside tune-skill. A test compares this page's code with that script on 1,342 skill folders, and they agree on every one.
--- lines.references/.references/, scripts/, examples/ and assets/ path the body names is in the folder. GitHub links only.The checker finds what a script can find. The harder problems need a reader: a description that promises what the body does not do, two skills that answer the same request, a handoff with no format. That is what a tune-up covers.
$0
The open skill we use for every tune-up. Your own agent runs it.
$19 per skill. Launch price, usually $29
We audit one skill by hand and send it back fixed.
$99 up to 5 skills
For skills that share a repo or hand work to each other.
Prices in USD, before any local taxes. Ordering opens an email to us; we reply with a secure payment link, and the clock starts when you pay. More than five skills, or private ones? See custom work.
Nowhere. The check is a script that runs in this page, and pasted text is never sent to us or stored. If you give a GitHub link, your browser fetches the public file directly from GitHub, or from jsDelivr's public mirror of GitHub when GitHub's lookup limit is used up. You can read the script at /check/check-core.js.
No. It means nothing in the file's shape is stopping it. Whether an agent picks your skill for the right request depends on what the description says and on the other skills installed beside it, and no script can judge that. Test it on real requests.
No. Fix every FAIL. A WARN is a question to answer: a skill with no neighbours does not need a "Not for" line, and a heading that differs from the name on purpose is fine.
One email with three things: your SKILL.md as a replacement file, a list of findings that each quote the line and give the smallest fix, and a short set of test requests that should and should not trigger the skill. We tell you which checks we ran and which we could not.
If the audit finds nothing worth changing, we refund the full amount without being asked. If you are unhappy with what you get back, reply within 14 days and we refund you. Refunds go back to the original payment method.
Yes. Paste the file into your order email with anything sensitive removed. We read it to do the work and do not publish or reuse it. We never need access to your repo, your systems or your API keys.
GitHub allows 60 anonymous lookups an hour from one network address, which a shared office or mobile network can use up. When that happens the page finds the skill through jsDelivr's public mirror instead and the check carries on. One check is skipped on that route, whether the files the body points to exist, and the result says so.
Tell us what it should do and what it does instead. For one skill it is $19 at the launch price (usually $29), back in two working days, refunded if we find nothing to change.