# Witness Fact Notarization

> 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.

## Facts

- Endpoint: POST https://witness.outbid.sh/witness
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/witness-fact-notarization-61e72ed1
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_Q7o9Tpba8gHRVufdwDEpy

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability witness-fact-notarization-61e72ed1 -d '<json body>'
```

Example prompt: Can you get an independent signed receipt attesting to this fact: 'Company XYZ agreed to deliver 500 units by June 30, 2025'? I need a cryptographic witness record I can reference later.

## When to prefer this

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.

## Known failure modes

- 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

## 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.

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/witness-fact-notarization-61e72ed1/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from witness.outbid.sh](https://www.zero.xyz/host/witness.outbid.sh/llms.txt)