# Agent402 A2A Card Validator

> Agent402 A2A Card Validator is a paid API for AI agents from agent402.tools, paid per call via x402, $0.002/call, status unknown (last checked 2026-09-15).

Validates an Agent Card JSON object against the A2A (Agent-to-Agent) specification, returning validity status, errors, warnings, and a summary

## Facts

- Endpoint: POST https://agent402.tools/api/a2a-card-validate
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/agent402-a2a-card-validator-4ff5cc77
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_gBDCQ4ewQVWm0Oz0EmvXc

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 agent402-a2a-card-validator-4ff5cc77 -d '<json body>'
```

Example prompt: Can you check if my agent card JSON is valid — here's the card object — and tell me if there are any errors or warnings I need to fix?

## When to prefer this

Use this endpoint when you need to verify that an Agent Card JSON document conforms to the A2A (Agent-to-Agent) specification before publishing or registering it. It is the right choice when debugging why an agent card is being rejected, or when building tooling that programmatically generates agent cards and needs to validate output. Prefer this over manual schema checking when you want actionable error messages and a parsed summary in one call.

## Known failure modes

- Malformed JSON input returns validation errors listing structural issues
- Missing required A2A fields trigger error entries in the errors array
- Unknown or unsupported skill definitions may generate warnings
- Empty card object returns valid:false with descriptive errors
- Passing a JSON string instead of object is supported but malformed strings fail

## How this service works

Validate an A2A (Agent2Agent protocol) Agent Card: required fields, skill shape, transport names, capability flags - spec v0.3 structural core. Returns errors, interop warnings, and a normalized summary (skills, interfaces, capabilities). Deterministic mini-A2A tooling - check a card before your agent trusts it.

## Output

Returns a JSON object with a boolean 'valid' field, an 'errors' array listing any spec violations, a 'warnings' array for non-fatal issues, and a 'summary' object containing the agent name and skill count parsed from the card.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "card": {
   "type": "object",
   "description": "the Agent Card JSON (object or JSON string)"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "valid": true,
  "errors": [],
  "summary": {
   "name": "Sample Weather Agent",
   "skillCount": 1
  },
  "warnings": []
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/agent402-a2a-card-validator-4ff5cc77/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from agent402.tools](https://www.zero.xyz/host/agent402.tools/llms.txt)