# ForgeSignals x402 Transaction Witness & Attestation

> ForgeSignals x402 Transaction Witness & Attestation is a paid API for AI agents from forgesignals.org, paid per call via x402, $0.02/call, status unknown (last checked 2026-09-14).

Acts as a third-party witness for x402 micropayment transactions: signs the endpoint's advertised price and payee at call time, optionally verifies a Base blockchain settlement transaction, and records a response hash as an asserted claim.

## Facts

- Endpoint: POST https://forgesignals.org/attest
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/forgesignals-x402-transaction-witness-attestation-92a3e881
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_thx5BZ_LpuMahcMlxxA6z

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 forgesignals-x402-transaction-witness-attestation-92a3e881 -d '<json body>'
```

Example prompt: Witness the x402 transaction I just made with https://api.example.com/data — the settlement tx hash on Base is 0xabc123..., submitted by the buyer, and here's the SHA256 of the response I got: d4f8e2....

## When to prefer this

Choose this endpoint when you need cryptographically-grounded, third-party evidence of an x402 micropayment interaction — specifically to prove what a given endpoint advertised (price, payee) at a specific moment in time, and to optionally bind an on-chain Base settlement transaction to that advertisement. It is not a reputation system or a fraud score — it produces labelled evidence. Prefer it over self-attestation when there is a dispute, audit requirement, or multi-party accountability need around x402 API payments. Retrieval and verification of existing attestations are free; only creation costs $0.02 USDC.

## Known failure modes

- Invalid or unreachable x402 endpoint URL — endpoint liveness check fails
- Settlement tx hash not found or not yet confirmed on Base
- Settlement tx amount or payee does not match what the endpoint advertised
- Malformed SHA256 format for response_sha256 field
- Rate limiting or quota exceeded for the $0.02 paid attestation calls
- Network timeout when querying the Base blockchain for tx verification

## How this service works

Third-party witness for an x402 transaction. Signs what the endpoint advertised right now, verifies a settlement transaction on Base against that advertised price and payee, and binds an optional party-submitted response hash - each claim labelled witnessed or asserted. Evidence, not a reputation score. Retrieval and verification of attestations are free.

## Output

An attestation record containing witnessed claims (what the endpoint advertised — price and payee — at the moment of the call) and optionally asserted claims (the caller-submitted response hash). Each claim is labelled as either 'witnessed' (independently verified by ForgeSignals) or 'asserted' (party-submitted, recorded but not independently proven). If a settlement_tx is provided, the result includes on-chain verification against Base confirming whether the USDC payment matches the advertised payee and price.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "url": {
   "type": "string",
   "description": "the x402 endpoint the transaction was with"
  },
  "submitted_by": {
   "type": "string",
   "description": "optional label for who is submitting (buyer/seller)"
  },
  "request_nonce": {
   "type": "string",
   "description": "optional nonce tying the attestation to one specific request"
  },
  "settlement_tx": {
   "type": "string",
   "description": "optional Base tx hash of the USDC payment to verify on-chain"
  },
  "response_sha256": {
   "type": "string",
   "description": "optional sha256 of the response body you received; recorded as an ASSERTED claim, never as proof"
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/forgesignals-x402-transaction-witness-attestation-92a3e881/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from forgesignals.org](https://www.zero.xyz/host/forgesignals.org/llms.txt)