{"uid":"cap_thx5BZ_LpuMahcMlxxA6z","slug":"forgesignals-x402-transaction-witness-attestation-92a3e881","name":"ForgeSignals x402 Transaction Witness & Attestation","description":"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.","url":"https://forgesignals.org/attest","method":"POST","headers":{},"bodySchema":{"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"}}},"responseSchema":null,"example":null,"exampleRequest":null,"tags":["x402"],"displayCostAmount":"0.02","displayCostAsset":"USDC","priceDynamic":false,"priceHint":null,"priceStatus":"priced","priceSource":"probe","requiresHandshake":false,"reviewCount":0,"rating":{"score":"0.00","successRate":"0.00","reviews":0,"stars":null,"state":"unrated"},"availabilityStatus":"unknown","priceObserved":null,"sessionDeposit":null,"pricing":{"kind":"static","summary":"$0.02/call","primary":{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.02","per":"call","confidence":"exact"},"accepted":[{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.02","per":"call","confidence":"exact"}]},"paymentMethods":[{"uid":"pm_YVha1fiYJmASgES_i31eE","protocol":"x402","methodType":"crypto","chain":"base","mode":"charge","costAmount":"0.02","costPer":"request","priority":0,"asset":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","unit":"request","depositMicros":null,"planRef":null}],"brandName":null,"brandSlug":null,"brandBaseUrl":null,"brandDocsUrl":null,"whatItDoes":"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.","exampleAgentPrompt":"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....","exampleUseCases":[{"title":"Buyer disputes advertised API price","prompt":"I just paid for an x402 API call at https://api.someprovider.com/query and I want a third-party witness to record what price and payee the endpoint was advertising right now — my Base settlement tx is 0xdeadbeef... and I'm the buyer submitting this."},{"title":"Seller proves delivery to client","prompt":"As the seller, I want ForgeSignals to attest that I responded correctly to an x402 request from https://myapi.io/endpoint — here's the sha256 of the response body I delivered: a1b2c3..., and the settlement transaction on Base is 0x99ffcc...."},{"title":"Audit trail for automated agent payments","prompt":"My agent just completed an x402 micropayment to https://dataservice.io/feed — please create an attestation binding nonce req-7f3a to the settlement tx 0x112233... so I have a tamper-evident audit record of exactly what was advertised and paid."}],"resultDescription":"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.","failureModes":["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"],"whenToPreferThis":"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.","instructions":null,"reviewSummary":null,"reviewSummaryHighlights":null,"reviewSummaryConcerns":null,"reviewSummaryGeneratedAt":null,"activationCount":0,"lastUsedAt":null,"lastSuccessfullyRanAt":null,"lastHealthCheckAt":"2026-09-14T12:34:02.866Z","isFirstParty":false}