x402 Notary — Cryptographic receipts for AI outputs

How a receipt is made

Hash. Sign. Seal. Anchor.

Four steps, each one checkable without trusting us. The order matters — that's why they're numbered.

01 · HASH

Canonical digest

Your prompt, response, model id, and timestamp are canonicalized and hashed. The raw text is discarded immediately.

sha256(canonical_json(record))

02 · SIGN

Ed25519 attestation

The notary signs the hash and timestamps with its published key. Verifiable offline, by anyone, forever.

GET /api/pubkey

03 · SEAL

Merkle batch

Receipts batch into a Merkle tree every 10 minutes. Yours gets an inclusion proof against the batch root.

proof → merkle_root

04 · ANCHOR

Base calldata

Batch roots are written to Base as calldata — public, timestamped, immutable. The chain is the witness, not us.

0xe9c2ff37…e508cfe58e

Privacy, by construction

“We notarize the hash, not your secrets.”

Nothing to leakPrompts, responses, and metadata are hashed, signed, and discarded. The database holds proof material only.

Nothing on-chain but rootsOnly 32-byte Merkle roots touch Base. Your content never appears on a public chain, hashed or otherwise.

You hold the contentVerification works by you supplying the original text. The notary can't reveal what it never kept.

Use it

Three ways in. Zero signups.

The first unpaid request returns an x402 challenge; your client signs a USDC authorization and retries. Settlement lands on Base in seconds, and the receipt arrives in the same response.

MCP · Claude, Cursor, any client

Local with auto-payment

Six tools; the free four need no wallet at all.

{
  "mcpServers": {
    "x402-notary": {
      "command": "npx",
      "args": ["-y", "@forgemeshlabs/x402-notary-mcp"],
      "env": { "WALLET_PRIVATE_KEY": "0x…" }
    }
  }
}

MCP · hosted, nothing to install

Remote endpoint

Free tools execute; paid tools return payment instructions.

https://notary.forgemesh.io/mcp

# streamable HTTP · stateless
# no auth, no config

HTTP · any x402 client

Raw API

Verification is a plain free POST from anywhere.

curl -s https://notary.forgemesh.io/api/verify \
  -H 'content-type: application/json' \
  -d '{"attestation_id":"att_…",
       "prompt":"…","response":"…",
       "model_id":"…"}'

Operation	Price	What you get
POST /api/notarize	$0.001	Signed attestation for one inference
POST /api/notarize/batch	$0.005	Up to 20 receipts in one call — audit-trail rate
POST /api/verify	free	Signature check, hash recompute, Merkle proof
GET /api/receipt/:id	free	Public proof material for any attestation
GET /api/stats	free	Live volume, top models, anchor status
GET /api/pubkey	free	The notary key — verify receipts offline