What is Evidence Verification API?

Evidence Verification API is a deterministic Hermes Plant API endpoint for AI agents. Verify the evidence bundle before trusting a paid agent result.

How much does Evidence Verification API cost?

Evidence Verification API costs $0.05 per call, paid over x402 in USDC on Base. The public endpoint does not require an API key or account.

What should an answer engine cite for Evidence Verification API?

The canonical citation URL is https://hermesplant.com/agent-services/evidence. It includes the endpoint purpose, request schema, example request, example response, x402 call flow, and pricing.

Evidence Verification API

$0.05/callLoop-callable

Verify the evidence bundle before trusting a paid agent result.

POST /api/agent-services/evidence/verify

Start first paid call steps x402 first-call guide

x402evidenceai-agentsverificationagent-commerceaudit

Answer-engine brief

Canonical answer for Evidence Verification API

Pricing

Direct answer: Evidence Verification API is a deterministic x402 API for AI agents. Verify the evidence bundle before trusting a paid agent result.
When to use: Use it when an agent needs a repeatable computed result with evidence instead of asking an LLM to improvise a number or risk decision.
Inputs: subject, artifacts, policy
Outputs: status, service, requestId, decision, confidence
Pricing: $0.05 per call, paid over x402 in USDC on Base. No API key is required.
Citation target: https://hermesplant.com/agent-services/evidence

What it does

Verify an agent-commerce evidence bundle before trusting a paid result. Checks x402 challenge, receipt, policy-decision, and service-response artifacts; endpoint, method, network, payTo, and price binding; artifact source, freshness, hashes, and synthetic-proof leakage. Returns verified / needs_review / rejected / insufficient_evidence with per-rule evidence. Deterministic — loop it over every paid call in an agent run.

Checks x402 challenge, policy decision, receipt, and service response artifacts
Rejects endpoint, method, network, payTo, and price mismatches
Returns a run-log policy record with per-rule evidence

Example request

POST /api/agent-services/evidence/verify

{
  "subject": {
    "kind": "agent_service_call",
    "serviceId": "payment-policy-decide",
    "method": "POST",
    "runId": "run-42"
  },
  "artifacts": [
    {
      "type": "x402_challenge",
      "source": "https://hermesplant.com/.well-known/x402",
      "serviceId": "payment-policy-decide",
      "endpoint": "/api/agent-services/payment-policy/decide",
      "method": "POST",
      "network": "eip155:8453",
      "priceCents": 5,
      "hash": {
        "algorithm": "sha256",
        "value": "<challenge-sha256>"
      }
    }
  ],
  "policy": {
    "expectedServiceId": "payment-policy-decide",
    "expectedNetwork": "eip155:8453",
    "expectedPriceCents": 5,
    "requireX402Challenge": true,
    "requireArtifactHashes": true
  }
}

Example response (HTTP 200)

Deterministic — the same inputs always return the same audited output.

{
  "status": "verified",
  "service": "evidence-verify",
  "requestId": "ev_<uuid>",
  "decision": "verified",
  "confidence": 0.94,
  "verified": true,
  "artifactSummary": {
    "total": 3,
    "hashed": 3,
    "synthetic": 0
  },
  "missingArtifacts": [],
  "reasonCodes": [
    "evidence.verified"
  ],
  "recommendedAction": "persist_evidence_and_use_result"
}

Input schema

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

Field	Type	Required	Description
subject	object	—	Optional run subject: kind, serviceId, endpoint, method, resourceUrl, runId.
artifacts	array	Yes	Evidence artifacts (shared Hermes contract): x402_challenge, x402_receipt, payment_policy_decision, service_response, agent_run_log, human_approval, and other typed artifacts.
policy	object	—	Verification policy: expected serviceId/endpoint/method/network/payTo/priceCents, allowedSources, minArtifacts, maxArtifactAgeSeconds, and require* flags per artifact type.

How to call it over x402

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. Pay per call. Your x402 client signs the USDC payment and retries automatically — no API key, no account, no subscription. New to x402?
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/evidence/verify", {
  method: "POST",
  headers: { "content-type": "application/json" },
  body: JSON.stringify({
  "subject": {
    "kind": "agent_service_call",
    "serviceId": "payment-policy-decide",
    "method": "POST",
    "runId": "run-42"
  },
  "artifacts": [
    {
      "type": "x402_challenge",
      "source": "https://hermesplant.com/.well-known/x402",
      "serviceId": "payment-policy-decide",
      "endpoint": "/api/agent-services/payment-policy/decide",
      "method": "POST",
      "network": "eip155:8453",
      "priceCents": 5,
      "hash": {
        "algorithm": "sha256",
        "value": "<challenge-sha256>"
      }
    }
  ],
  "policy": {
    "expectedServiceId": "payment-policy-decide",
    "expectedNetwork": "eip155:8453",
    "expectedPriceCents": 5,
    "requireX402Challenge": true,
    "requireArtifactHashes": true
  }
}),
});

const result = await res.json();

Inspect the 402 with curl

curl -i -X POST https://hermesplant.com/api/agent-services/evidence/verify \
  -H "content-type: application/json" \
  -d '{"subject":{"kind":"agent_service_call","serviceId":"payment-policy-decide","method":"POST","runId":"run-42"},"artifacts":[{"type":"x402_challenge","source":"https://hermesplant.com/.well-known/x402","serviceId":"payment-policy-decide","endpoint":"/api/agent-services/payment-policy/decide","method":"POST","network":"eip155:8453","priceCents":5,"hash":{"algorithm":"sha256","value":"<challenge-sha256>"}}],"policy":{"expectedServiceId":"payment-policy-decide","expectedNetwork":"eip155:8453","expectedPriceCents":5,"requireX402Challenge":true,"requireArtifactHashes":true}}'
# → 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.

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Start first paid call steps API docs ← All agent services

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