Assurance Attest

What it does

Signed receipt for one agent action. Post an x402 payment intent or MCP tool call (optional policy + settlement outcome) and get a canonical HMAC-signed record: binding hash, verdict, findings, and a free public verify URL third parties can check without trusting your agent's logs. Loop it after every payment or tool call to build a tamper-evident audit trail. Canonicalization hermes-stable-json-v1; org history and probes available on Assurance plans.

• ✓Binds an x402 payment or MCP tool call to a canonical HMAC-signed record
• ✓Optional policy evaluation and settlement outcome in the same record
• ✓Free public verify endpoint — third parties check it without trusting your logs

Input schema

Top-level request fields. Nested shapes are shown in the example above and the OpenAPI spec.

How to call it over x402

1. 1. Send the request. The first unpaid call returns HTTP 402 with an x402 payment challenge — $0.05, USDC on Base, and the recipient.
2. 2. Pay per call. Your x402 client signs the USDC payment and retries automatically — no API key, no account, no subscription. New to x402?
3. 3. Read the result. HTTP 200 returns the computed values plus evidence-backed findings.

With the x402 fetch client (Node / TypeScript)

import { wrapFetchWithPayment } from "@x402/fetch";
import { privateKeyToAccount } from "viem/accounts";

const account = privateKeyToAccount(process.env.AGENT_WALLET_KEY);
const pay = wrapFetchWithPayment(fetch, account); // USDC on Base

const res = await pay("https://hermesplant.com/api/agent-services/assurance/attest", {
  method: "POST",
  headers: { "content-type": "application/json" },
  body: JSON.stringify({
  "protocol": "x402",
  "subject": {
    "runId": "run-42",
    "purpose": "enrich leads"
  },
  "intent": {
    "resourceUrl": "https://api.example.com/search",
    "method": "POST",
    "network": "eip155:8453",
    "amountUnits": "7000",
    "payTo": "0x6d6E695b09861467c7d462f5AAF31cF3540B9192"
  },
  "outcome": {
    "outcome": "fulfilled",
    "settlementId": "0xsettle",
    "responseStatus": 200
  }
}),
});

const result = await res.json();

Inspect the 402 with curl

curl -i -X POST https://hermesplant.com/api/agent-services/assurance/attest \
  -H "content-type: application/json" \
  -d '{"protocol":"x402","subject":{"runId":"run-42","purpose":"enrich leads"},"intent":{"resourceUrl":"https://api.example.com/search","method":"POST","network":"eip155:8453","amountUnits":"7000","payTo":"0x6d6E695b09861467c7d462f5AAF31cF3540B9192"},"outcome":{"outcome":"fulfilled","settlementId":"0xsettle","responseStatus":200}}'
# → HTTP/1.1 402 Payment Required  (x402 challenge: price, USDC asset, Base network, recipient)
# → sign the USDC-on-Base payment and retry to receive HTTP 200

Prefer no wallet? Get a free API key (250 calls/mo) and send it as X-API-Key instead of signing an x402 payment — the same call, no crypto, ideal for looping over many records.

Prefer zero code? This endpoint is also exposed as a tool on the Hermes Plant MCP server, so an MCP-capable agent can call it with its own x402 wallet.