# A2A Agent Card Verifier

> A2A Agent Card Verifier is a paid API for AI agents from agents.daedalusdevelopmentgroup.com, paid per call via x402, $0.01/call, status unknown (last checked 2026-10-21).

Verifies an A2A agent card by dual-probing well-known endpoints, validating required fields, classifying protocol version, detecting schema breaks, and verifying JWS signatures via did:web key resolution.

## Facts

- Endpoint: POST https://agents.daedalusdevelopmentgroup.com/v1/a2a/verify-card?utm_source=zero.xyz
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-21
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/a2a-agent-card-verifier-b9008278
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_WssqUnU1fVn80GiS2pYgZ

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 a2a-agent-card-verifier-b9008278 -d '<json body>'
```

Example prompt: Before I route any work to this new agent at https://myagent.example.com, can you verify its agent card — check all the required fields, flag any 0.3-to-1.0 schema breaks, verify the JWS signature, and live-probe its tasks/send interface?

## When to prefer this

Use this endpoint when you need to trust or route work to an A2A agent whose card you have not previously validated — especially when the agent card could be from an untrusted or third-party source. Prefer it over manual field inspection when you need cryptographic JWS signature verification via did:web, detection of the known silent schema breaks between A2A protocol versions 0.3 and 1.0, or a live interface probe of tasks/send. It is the right choice for building agent registries, trust gates, or automated onboarding pipelines that must validate agent cards programmatically before routing.

## Known failure modes

- Agent card URL unreachable or returns non-200 status
- Neither /.well-known/agent-card.json nor agent.json found at the target host
- Required MUST fields missing from the agent card (name, description, url, version, capabilities)
- JWS signature present but did:web key resolution fails
- Signature verification fails due to invalid canonical bytes or mismatched key
- tasks/send live probe returns unexpected error or timeout
- Unknown or unsupported protocolVersion value
- Malformed JSON in the agent card body

## How this service works

Verify an A2A agent card before trusting or routing to it: dual-probe /.well-known/agent-card.json and agent.json, check MUST fields (name/description/url/version/capabilities), classify protocolVersion, flag the known 0.3<->1.0 silent schema breaks, verify any JWS signature over RFC 8785 JCS canonical bytes (did:web key resolution), and live-probe the advertised interface with tasks/send. Per-step verdict + remediation.

## Output

A structured per-step verdict report covering: dual-probe results for /.well-known/agent-card.json and agent.json, MUST-field presence checks (name, description, url, version, capabilities), protocolVersion classification, flagged 0.3-to-1.0 silent schema breaks, JWS signature verification result with did:web key resolution status, and a live tasks/send probe outcome — each step accompanied by remediation guidance.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input",
  "output"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method",
    "bodyType",
    "body"
   ],
   "properties": {
    "body": {
     "type": "object"
    },
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "POST",
      "PUT",
      "PATCH"
     ],
     "type": "string"
    },
    "bodyType": {
     "enum": [
      "json",
      "form-data",
      "text"
     ],
     "type": "string"
    }
   },
   "additionalProperties": true
  },
  "output": {
   "type": "object",
   "required": [
    "type",
    "example"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "ok": true
    }
   },
   "additionalProperties": true
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "ok": true
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/a2a-agent-card-verifier-b9008278/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from agents.daedalusdevelopmentgroup.com](https://www.zero.xyz/host/agents.daedalusdevelopmentgroup.com/llms.txt)