# Agent Card Validator (A2A) by Synthora

> Agent Card Validator (A2A) by Synthora is a paid API for AI agents from agentcard.hergertsynthora.com, paid per call via x402, $0.01/call, status unknown (last checked 2026-09-15).

Validates an A2A Agent Card URL or JSON against the A2A specification, returning a compatibility score, schema errors, and warnings

## Facts

- Endpoint: POST https://agentcard.hergertsynthora.com/service
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/agent-card-validator-a2a-by-synthora-8d5a8386
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_jdFqRgbA0OJIU-buCSM6J

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-validator-a2a-by-synthora-8d5a8386 -d '<json body>'
```

Example prompt: Can you validate my A2A agent card at https://myagent.example.com/.well-known/agent-card.json and tell me the compatibility score, any schema errors, and whether my security scheme and endpoint are properly configured?

## When to prefer this

Use this endpoint when you need to deterministically validate an A2A Agent Card against the official spec before publishing or integrating it — especially when you need a signed compatibility score for trust verification, endpoint reachability confirmation, or skill schema compliance checking in the agent economy.

## Known failure modes

- Invalid or unreachable URL returns endpoint reachability error
- Malformed JSON in card field returns parse error
- Agent card missing required fields returns schema_errors with details
- Network timeout on reachability check returns warning
- Payment not processed (x402) returns 402 response

## How this service works

Agent Card Validator (A2A): given an Agent Card URL or JSON, deterministically validates it against the A2A spec — required fields, skill schemas, endpoint reachability, security schemes, provider transparency — and returns a compatibility_score, schema_errors and warnings. The trust layer for the agent economy. Deterministic, Ed25519-signed. 0.01 USDC via x402 on Base. SYNTHORA.

## Output

Returns a compatibility_score (numeric, Ed25519-signed), a list of schema_errors identifying spec violations (missing required fields, malformed skill schemas, invalid security schemes), and warnings for soft issues like provider transparency gaps and unreachable endpoints.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "url": {
   "type": "string",
   "description": "URL of the A2A Agent Card (.well-known/agent-card.json)"
  },
  "card": {
   "type": "object",
   "description": "Or paste the Agent Card JSON directly"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "ok": true,
  "niche": "agent_card",
  "result": {
   "signed": "ed25519",
   "verdict": "buena",
   "warnings": [
    "falta campo recomendado: documentationUrl"
   ],
   "skills_count": 1,
   "schema_errors": [],
   "a2a_conformant": true,
   "endpoint_status": 200,
   "pricing_declared": false,
   "security_declared": true,
   "compatibility_score": 82
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/agent-card-validator-a2a-by-synthora-8d5a8386/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from agentcard.hergertsynthora.com](https://www.zero.xyz/host/agentcard.hergertsynthora.com/llms.txt)