Attest a settled call on Base

Write an on-chain attestation (Ethereum Attestation Service on Base) that binds a call you paid for to the bytes you received: the tool slug, sha256 of the JSON response, the settlement chain and transaction, the payer, the time served and the price, signed by this server's wallet. Send POST /api/attest with the required field tx and pay $0.050 per call over x402 with USDC on an EVM chain (the paying wallet is the identity). It returns a JSON object with uid, attestationUrl, attestTx, block, existing and 7 more.

Give it the settlement transaction from the PAYMENT-RESPONSE (or Payment-Receipt) header of any settled call; the attestation UID and its public page on base.easscan.org come back. Use it when an agent has to prove afterwards what data it acted on. Only the buyer can attest a sale: this call must be paid with a signed EVM authorization from the same wallet, and sales of wallet-scoped routes (memory, usage) are never attestable. The record is public and permanent: it names the payer and the tool. One attestation per sale (a repeat returns the existing UID); refused, uncharged, when the transaction is not a sale of this server, when the response was streamed or binary, or when Base gas would exceed the tool's own ceiling.

Category: Routing & delegation · Tags: attestation eas provenance receipt audit base x402

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Parameters

Example request

curl -i -X POST https://agent402.tools/api/attest \
  -H "Content-Type: application/json" \
  -d '{"tx":"0x2f1fecade9bd945e7817c11e5a34cafe6b349dd8c92a7587efed1de476bddfeb"}'

Without payment this returns HTTP 402 Payment Required with the exact price for attest; any x402 v2 or MPP client pays it and retries.

Example response

{
  "uid": "0x5b4d0c1e8f7a4c2d9e0b6a3f1c8d7e6b5a4f3e2d1c0b9a8f7e6d5c4b3a2f1e0d",
  "attestationUrl": "https://base.easscan.org/attestation/view/0x5b4d0c1e8f7a4c2d9e0b6a3f1c8d7e6b5a4f3e2d1c0b9a8f7e6d5c4b3a2f1e0d",
  "attestTx": "0x9c8b7a6f5e4d3c2b1a0f9e8d7c6b5a4f3e2d1c0b9a8f7e6d5c4b3a2f1e0d9c8b",
  "block": "50829611",
  "existing": false,
  "attester": "0x77065d81e18ad403BCD6e9A0616b288e16744121",
  "chain": "eip155:8453",
  "eas": "0x4200000000000000000000000000000000000021",
  "schemaUid": "0x2a4e6c8d0f1b3a5c7e9d1f3b5a7c9e1d3f5b7a9c1e3d5f7b9a1c3e5d7f9b1a3c",
  "schema": "string slug,bytes32 responseSha256,string settlementNetwork,string settlementTx,string payer,uint64 servedAt,uint64 priceMicroUsd",
  "data": {
    "slug": "crypto-price",
    "responseSha256": "0x7d2a9b1c4e6f8a0b2c4d6e8f0a1b3c5d7e9f1a3b5c7d9e1f3a5b7c9d1e3f5a7b",
    "settlementNetwork": "eip155:8453",
    "settlementTx": "0x2f1fecade9bd945e7817c11e5a34cafe6b349dd8c92a7587efed1de476bddfeb",
    "payer": "0x902dcf34e53695bdea2ffb354b1a2e58bd598256",
    "servedAt": "2026-09-03T15:16:06.000Z",
    "priceUsd": 0.01
  },
  "verify": {
    "responseDigest": "sha256 over the exact JSON bytes you received for that call; compare with responseSha256",
    "payment": "follow settlementTx on eip155:8453: the payer paid this server's payTo",
    "attestation": "fetch the UID on https://base.easscan.org (or read EAS 0x4200000000000000000000000000000000000021 on Base): attester must be this server's wallet, schema must match"
  }
}

From an MCP client

catalog.call {
  "slug": "attest",
  "params": {
    "tx": "0x2f1fecade9bd945e7817c11e5a34cafe6b349dd8c92a7587efed1de476bddfeb"
  }
}

The hosted connector at https://agent402.tools/mcp needs a payment for attest; the stdio package pays it from a wallet or from AGENT402_CREDITS_KEY (wallet only for this tool). Local install: npx -y agent402-mcp.

Errors and behavior

• tx is required. An input the tool rejects returns an HTTP 4xx whose body carries error, tool, expected, required and example, so the caller can correct it.
• A paid call that ends in any status of 400 or above is not charged over x402 or MPP: settlement is cancelled when the tool fails.
• Wallet-only: this tool reaches the network or stored state, so it has no proof-of-work tier.
• Identity-bound: results are keyed to the wallet that signed the payment, so only EVM x402 payments are accepted; credits keys and Tempo are refused.
• A GET or HEAD to /api/attest returns the same 402 quote, so the price can be read without a body.
• An Idempotency-Key header makes a retried paid call replay the first 200 instead of charging again (an answer larger than 1 MB is not replayed).

Paid call (JavaScript agent)

import { wrapFetchWithPayment } from "@x402/fetch";
import { x402Client } from "@x402/core/client";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

const client = new x402Client();
client.setSpendControls?.(false); // keep your own spending ceiling in code
registerExactEvmScheme(client, { signer: privateKeyToAccount(KEY) });
const payFetch = wrapFetchWithPayment(fetch, client);

const res = await payFetch("https://agent402.tools/api/attest", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "tx": "0x2f1fecade9bd945e7817c11e5a34cafe6b349dd8c92a7587efed1de476bddfeb"
  }),
});

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