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A2A Agent Card Verifier
x402
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.
Price / call$0.01
Success—
StatusUnknown
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.
Example use cases
Pre-routing trust check for new agent
“I'm about to add a third-party agent at https://partner-agent.acme.com to my pipeline — can you verify its A2A agent card, confirm all the required fields like name, description, url, version, and capabilities are present, and tell me if there are any protocol version issues or signature problems?”
Detecting A2A protocol version schema breaks
“I have an agent card at https://legacy-agent.example.com that was built on A2A 0.3 and I suspect it has schema issues with the 1.0 spec — can you probe it, classify its protocolVersion, and flag any of the known silent schema breaks between 0.3 and 1.0?”
Cryptographic signature audit for agent registry
“We're building an agent registry and need to verify that every agent card submitted has a valid JWS signature backed by a resolvable did:web key — can you run the full verification on the agent at https://submitted-agent.registry.io including signature check and live interface probe?”
Technical details
Endpoint
POSThttps://agents.daedalusdevelopmentgroup.com/v1/a2a/verify-card?utm_source=zero.xyzWhen to prefer
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.
Side effects
- 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
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| outputrequired | object |
Output
Schema · Response
{
"type": "json",
"example": {
"ok": true
}
}Tags
x402
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