Verify a Claude Agent Skill.
Check whether a Claude Agent Skill is registered in the public ledger. Search by registration number (SA-YYYY-NNNNNN) or by the SHA-256 fingerprint of the .mdc or SKILL.md file. Free, instant, no account required.
Need to compute a SHA-256 hash? See the command-line examples below.
Three reasons to check before you trust.
Confirm authorship
Someone sent you a Claude Skill they claim to have authored. Look up the registration number — you'll see the original author name and the registration date, anchored cryptographically.
Detect modifications
If the SHA-256 fingerprint of the file you have doesn't match the one on the certificate, the file has been modified — even by a single character. The hash never lies.
Check before publishing
Before publishing a Skill or licensing one, verify it's not already registered by someone else. A two-second hash check prevents an authorship dispute later.
Bytes in, bytes out. No trust required.
Every registration is content-addressed by the SHA-256 hash of the exact bytes of the .mdc or SKILL.mdfile. Identical bytes produce identical hashes; any change — even a single character — produces a completely different fingerprint. Compute the hash locally, compare against what's on the certificate and at /v/<reg>, and you have a yes/no answer that doesn't require trusting SkillAuthor.
# macOS / Linux
shasum -a 256 my-skill.mdc
# Windows PowerShell
Get-FileHash my-skill.mdc -Algorithm SHA256Paste the 64-character hex output into the search box above. If a registration exists, you'll land on its public verification page.
Common questions.
- Is verification free?
- Yes. Verifying any registration on the Claude Agent Skills Registry is free and instant. No account, no API key, no login.
- How do I find the registration number?
- The registration number is in the format
SA-YYYY-NNNNNN. It's printed on the PDF certificate, in the certificate filename, and shown at the top of every public verification page. - What if I only have the .mdc file?
- Compute its SHA-256 hash locally with
shasum -a 256 your-skill.mdcand paste the 64-character hex string into the search box. If the file is registered, you'll be taken straight to its verification page. - What does it mean if no registration is found?
- The exact bytes of that file have never been registered with SkillAuthor. Anyone — including you — can register theirs for $39 one-time.
- Can I verify without using skillauthor.com?
- Yes. The PDF certificate is self-contained: it carries the SHA-256 fingerprint on its face. Run
shasum -a 256on the original file locally and compare against the hash on the certificate. No internet required.
Need to register a skill?
Verification is for skills already on the Claude Agent Skills Registry. To add your own — $39 one-time, permanent record, QR-coded certificate, semantic near-duplicate protection.