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Witness Fact Notarization
x402
Witness Fact Notarization is a paid API for AI agents from witness.outbid.sh, paid per call via x402, $0.01/call, status unknown (last checked 2026-09-14).
Creates an independently signed receipt attesting to a fact or statement, providing cryptographic proof of witnessing at a point in time.
Price / call$0.01
Success—
StatusUnknown
How this service works
Paid, attributable, perishable observation of public web facts. Run POST /quote first (free): a 200 means the experiment can be performed; only then pay POST /witness ($0.01 USDC via x402, Base or Solana) for a signed receipt. Receipts bind their full method, expire in 1h, and are rendered with contradictions and expiry visible at GET /observatory. Agent docs: /llms.txt and /skill.md. Signing key: GET /pubkey. Payment descriptor: GET /.well-known/x402. robots.txt disallows /witness for crawlers.
Output
A signed receipt containing a cryptographic attestation of the submitted fact or statement, including a timestamp and independent signature that can be used to prove the fact was witnessed at a specific point in time.
Example use cases
Legal agreement timestamp proof
“I need to record and independently witness the fact that our contract terms were agreed upon today — can you get a signed receipt attesting to: 'Client Acme Corp accepted terms v2.3 on 2025-06-15'?”
AI agent output provenance
“Can you get a witness receipt for this AI-generated report summary so I can prove what the model said at this exact moment: 'Risk assessment score: 7.2, generated by model v4.1 on 2025-06-15'?”
Audit trail for data pipeline
“I need a cryptographic attestation that this data hash existed at this point in time — please witness the fact: 'Dataset checksum sha256:abc123def456 was validated clean at pipeline step 3 on 2025-06-15'.”
Technical details
Endpoint
POSThttps://witness.outbid.sh/witnessWhen to prefer
Choose this endpoint when you need an independent, cryptographically signed attestation of a fact or statement at a specific moment in time — particularly for audit trails, legal evidence, AI output provenance, or any situation where a trusted third-party witness signature adds value. Prefer this over simple hashing or self-signed records when independent verification and non-repudiation are required.
Side effects
- Payment not included or insufficient USDC — request rejected with 402
- Empty or missing fact/statement body — validation error
- Malformed request payload — 400 bad request
- Service unavailable — 503 or timeout
- Receipt signing failure — internal error on the provider side
Tags
x402
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