# Agent Card Witness — AI Agent Identity Verification

> Agent Card Witness — AI Agent Identity Verification is a paid API for AI agents from witness.holoweave.org, paid per call via x402, $0.01/call, status down (last checked 2026-09-15).

Fetches, verifies, and cryptographically attests to an AI agent's published agent card, detecting changes in card content or skills since a previous check.

## Facts

- Endpoint: POST https://witness.holoweave.org/v1/agent-card-witness
- Price: $0.01/call
- Payment: x402
- Status: down
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/agent-card-witness-ai-agent-identity-verification-21654892
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_mcLZtuhZPsoNUxbKKKHXf

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 agent-card-witness-ai-agent-identity-verification-21654892 -d '<json body>'
```

Example prompt: Can you fetch and verify the agent card for https://agent.example.com and give me a signed attestation of its current contents — I want to know if the card digest has changed from 4c1a… that I saw last week.

## When to prefer this

Use this endpoint when you need an independent, cryptographically signed third-party attestation of an AI agent's published identity card — especially for auditing, trust establishment, or change-detection workflows. Prefer it over fetching the agent card yourself when you need tamper-evident proof, when you want to detect capability drift across time using digest comparison, or when downstream systems require a signed witness record rather than a raw HTTP fetch.

## Known failure modes

- Agent card URL is unreachable or returns non-200 status — attestation includes the HTTP status and a failed verdict
- Card JSON is malformed or missing required fields — witness returns an error evidence block
- Expected digest provided but card has changed — verdict is CHANGED rather than UNCHANGED
- Invalid or non-HTTPS URL provided — request rejected with validation error
- Agent card host is behind a bot-blocking rule — fetch may fail or return unexpected content
- Payment of $0.01 USDC not provided or rejected — 402 Payment Required response

## How this service works

Web bot auth debugging for AI agents, priced per check at $0.01. RFC 7638 keyid thumbprint verification, RFC 9421 Ed25519 signature verification, and per-verifier acceptance rules. Signed attestations, published fixtures, sources with dates.

## Output

A signed JSON attestation containing: an ed25519 signature (algorithm, base64 value, key ID), and an attestation body with verdict ('pass'/'fail'), the fetched card URL, card metadata (name, version, interfaces, skill IDs with digests, skill count, card digest), HTTP status, and optionally a comparison result (unchanged/changed vs. the expected digest or skill map).

## Response schema (JSON Schema)

```json
{
 "example": {
  "signature": {
   "alg": "ed25519",
   "value": "base64...",
   "key_id": "aw-attest-2026-08"
  },
  "attestation": {
   "verdict": "pass",
   "endpoint": "agent-card-witness",
   "evidence": {
    "url": "https://agent.example.com/.well-known/agent-card.json",
    "card": {
     "name": "Recipe Agent",
     "skills": {
      "plan-week": "91ac…",
      "find-recipe": "7de0…"
     },
     "version": "1.0.0",
     "interfaces": [
      {
       "url": "https://agent.example.com/a2a",
       "transport": "JSONRPC"
      }
     ],
     "signatures": [],
     "card_digest": "4c1a…",
     "skill_count": 2
    },
    "status": 200,
    "comparison": {
     "unchanged": true,
     "expect_digest": "4c1a…"
    }
   }
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/agent-card-witness-ai-agent-identity-verification-21654892/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from witness.holoweave.org](https://www.zero.xyz/host/witness.holoweave.org/llms.txt)