How to Prove You Created Your Claude Agent Skill in 2026.

By mid-2026, AI Agent Skills — small .mdc and SKILL.md files that teach Claude or another agent framework a specific competency — are real intellectual property. The good ones get reused, forked, copied, and occasionally claimed by someone else. A practical question follows: if someone later says they authored your Skill, what do you actually have to push back with?

This guide walks through what authorship proof means for Agent Skills, the cryptographic primitives that matter, the approaches developers actually use (most of them weaker than they look), and a step-by-step process for registering a Claude Agent Skill in a way that anyone can independently verify.

What “proving authorship” actually means

The phrase “proving authorship” gets used loosely. In practice it splits into two related but different claims:

• Existence at time T. A specific file existed, in a specific form, at a specific moment. This is a factual claim about bytes and time.
• Attribution to person P. A specific person asserted authorship of that file at that time. This is a social claim, recorded as a name on a record.

Authorship proof systems can't replace copyright law, which arises automatically when a work is fixed. What they do is generate independent, machine-checkable evidence that shifts the burden of disproof onto anyone who later claims the work was theirs. If your file existed (bit-for-bit) on date X and theirs shows up on date Y > X, that's a fact a third party can verify without trusting either of you.

For Claude Agent Skills specifically, the unit of proof is the file itself: the exact bytes of your .mdc or SKILL.md. Comments, frontmatter, tool definitions, prompt scaffolding — all of it. Change a single character and the proof targets a different artefact.

The cryptographic primitives that actually matter

The technology underneath any credible authorship system is surprisingly small. Three pieces.

SHA-256 — what it does and doesn't do

SHA-256 produces a 256-bit fingerprint of any byte sequence. Two identical files always produce the same fingerprint; two files differing by even a single character produce completely different fingerprints. Reverse-engineering a file from its fingerprint is computationally infeasible.

That last property matters. The hash is a one-way commitment: publishing the hash is equivalent to publishing the file from a “you can verify but can't reconstruct” standpoint. Combined with a timestamp, the hash anchors a specific artefact to a specific moment.

What SHA-256 doesn't do: it doesn't prove who created the file, and it doesn't prove the file is original. It proves that this exact byte sequence existed when the hash was computed.

UTC timestamps — and why they're worth bothering with

A hash on its own only says “this file existed somewhere, sometime.” A timestamp pins it to a moment. The only timestamps worth anything in this context are timestamps you can't backdate: ones recorded by an independent third party, in UTC, with second-level precision.

Self-signed timestamps (a date stamp in your own log file, a comment in your README) don't carry weight in a dispute because you control both the file and the timestamp. The point of a registry is exactly to break that loop — a timestamp recorded somewhere you can't edit after the fact.

Public verification URLs

The last piece is verifiability without trust. Anyone — a collaborator, a journalist, a court — should be able to start with two things: your file and your registration number, and arrive at a yes/no answer without contacting you or trusting any single party.

Concretely: a public URL of the form /v/<reg> resolves to a page showing the hash, timestamp, declared author name, and filename. A verifier runs shasum -a 256 the-file.mdclocally, compares to the hash on the page, and that's it. No accounts, no signed JWTs, no API keys. The PDF certificate carries the same hash on its face — so even if the verifier can't reach the registry online, the cert is self-contained evidence.

Approaches developers actually use

Most developers reach for one of three approaches when they want authorship proof. The first two have well-known weaknesses worth understanding.

1. Git commit history

A git repository's commit graph records when files were added and modified. For open-source authors, this is the de facto authorship proof: the public commit dates on a GitHub repository are independently observable and hard to backdate (GitHub records receive-time, not commit-time, in many surface areas).

The weakness: git timestamps are commit metadata you control. A local commit can be backdated trivially with GIT_COMMITTER_DATE. Public push timestamps are harder to fake but only matter once you've actually pushed, and many Agent Skills live in private repos or are shared as standalone files. If your Skill was developed internally before going public, your push date doesn't prove first authorship.

2. Internal docs, screenshots, Slack timestamps

A surprising number of developers rely on internal artefacts: “I have a screenshot from January,” “our Notion has the timestamp,” “the Slack message dates it.” These don't survive contact with adversarial examination. Internal systems can be edited; the burden of proving non-tampering falls on you, and most teams can't actually meet it.

3. A cryptographic registry

The third approach is registering the file with an independent service that records the SHA-256 hash and a UTC timestamp, then publishes a verification URL. The Claude Agent Skills Registry (SkillAuthor) is one such service, designed specifically for .mdc and SKILL.md files.

The mechanics are deliberately simple: the file is hashed in your browser before upload, the registry hashes it again on receipt to confirm, a payment closes the registration, and a PDF certificate is issued with the hash, timestamp, registration number, and a QR code. The hash and timestamp are then publicly resolvable via a permanent URL.

Step-by-step: registering your Claude Agent Skill

Step 1 — Hash your file locally first

Before you upload anything, prove to yourself that you know what you're registering. Run:

shasum -a 256 your-skill.mdc

Copy the 64-character hex string. This is what should appear on your certificate. If the registry returns a different hash, something went wrong — the bytes that arrived are not the bytes you intended to send.

Step 2 — Submit through the registry form

On the register page, drop the file. Your browser computes SHA-256 locally and shows you the hash before the file leaves the page. This is by design: you get instant feedback about what's being registered, and you can compare against the hash you computed in Step 1.

The form also runs an exact-duplicate check at this point. If someone has already registered the byte-identical file, you see a warning showing their registration number and date — you can still proceed with your own registration (each registration is its own ledger entry), but you go in informed.

Then supply your author name and email. The name is what gets printed on the certificate. The email is for the receipt and for any near-duplicate alert correspondence; it's not published.

Step 3 — Complete payment and receive the certificate

Payment is a one-time $39 USD via Stripe Checkout. As soon as Stripe confirms the payment, the registry handler runs a single database transaction that mints a sequential registration number (format SA-YYYY-NNNNNN), sets the registered-at timestamp to the second, and records the hash. By design, this is atomic: two concurrent payment confirmations for the same checkout session cannot both produce registrations, and the registration number cannot ever be duplicated.

You then receive a PDF certificate via email and as a download on the success page. The certificate carries: registration number, your declared name, filename, SHA-256 fingerprint, UTC timestamp, and a QR code that resolves to the public verification page at /v/<reg>.

How third parties (including a court) verify your claim

The protocol for an independent verifier is intentionally short:

1. Obtain the file in question — the original .mdc or SKILL.md you registered.
2. Run shasum -a 256 file.mdc locally.
3. Open the public verification page (printed on the certificate) or scan the QR code. Compare the hash shown there with the hash produced in step 2.
4. A match means the bytes are identical, and the registry timestamp tells the verifier when those exact bytes were committed. A mismatch means the file in question is not the registered one.

The PDF certificate is self-contained — it carries the hash and timestamp on its face, so even if the registry is unreachable, the cert can be checked against any copy of the original file. That's the property that makes the proof durable.

What to do today

If you ship Claude Agent Skills — open source, internal, or commercial — registering each meaningful version is cheap, permanent, and gives you something concrete to point at later. $39 one-time, no accounts, no subscriptions, and the registration sticks around regardless of whether SkillAuthor does. Register the version you care about now, before you need the proof.