A2A Agent Card validate

Validate an A2A (Agent2Agent protocol) Agent Card: required fields, skill shape, transport names, capability flags - spec v0.3 structural core. Send POST /api/a2a-card-validate with the required field card and pay $0.002 per call over x402 or MPP, or call it free by solving a proof-of-work challenge. It returns a JSON object with valid, errors, warnings and summary.

Returns errors, interop warnings, and a normalized summary (skills, interfaces, capabilities). Deterministic mini-A2A tooling - check a card before your agent trusts it.

Category: Live public data · Tags: a2a agent2agent agent-card validate interop protocol agents

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Parameters

Example request

curl -i -X POST https://agent402.tools/api/a2a-card-validate \
  -H "Content-Type: application/json" \
  -d '{"card":{"protocolVersion":"0.3.0","name":"Sample Weather Agent","description":"A sample A2A Agent Card served as a static example for card tooling. This describes a fictional weather agent, not a live A2A endpoint.","url":"https://example.com/a2a/v1","preferredTransport":"JSONRPC","version":"1.0.0","provider":{"organization":"Example Org","url":"https://example.com"},"capabilities":{"streaming":true,"pushNotifications":false,"stateTransitionHistory":false},"defaultInputModes":["application/json","text/plain"],"defaultOutputModes":["application/json"],"skills":[{"id":"get-forecast","name":"Get weather forecast","description":"Returns a city'\''s 5-day forecast.","tags":["weather","forecast"],"examples":["What is the weather in Paris this week?"]}]}}'

Without payment this returns HTTP 402 Payment Required with the exact price for a2a-card-validate; any x402 v2 or MPP client pays it and retries.

Example response

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

From an MCP client

catalog.call {
  "slug": "a2a-card-validate",
  "params": {
    "card": {
      "protocolVersion": "0.3.0",
      "name": "Sample Weather Agent",
      "description": "A sample A2A Agent Card served as a static example for card tooling. This describes a fictional weather agent, not a live A2A endpoint.",
      "url": "https://example.com/a2a/v1",
      "preferredTransport": "JSONRPC",
      "version": "1.0.0",
      "provider": {
        "organization": "Example Org",
        "url": "https://example.com"
      },
      "capabilities": {
        "streaming": true,
        "pushNotifications": false,
        "stateTransitionHistory": false
      },
      "defaultInputModes": [
        "application/json",
        "text/plain"
      ],
      "defaultOutputModes": [
        "application/json"
      ],
      "skills": [
        {
          "id": "get-forecast",
          "name": "Get weather forecast",
          "description": "Returns a city's 5-day forecast.",
          "tags": [
            "weather",
            "forecast"
          ],
          "examples": [
            "What is the weather in Paris this week?"
          ]
        }
      ]
    }
  }
}

On the hosted connector at https://agent402.tools/mcp, catalog.call runs a2a-card-validate free (rate-limited, no wallet). Local install: npx -y agent402-mcp.

Errors and behavior

• card is required. An input the tool rejects returns an HTTP 4xx whose body carries error, tool, expected, required and example, so the caller can correct it.
• A paid call that ends in any status of 400 or above is not charged over x402, MPP or a prepaid credits key: settlement is cancelled when the tool fails. The exception is a Tempo push credential, a transfer the buyer sent before the call: it settles before the tool runs, so if the tool then fails the payment is recorded as a refund owed to the paying wallet.
• Free tier: no outbound network call leaves the server for this tool, so proof-of-work (16 leading zero bits of sha256) pays for it.
• A GET or HEAD to /api/a2a-card-validate returns the same 402 quote, so the price can be read without a body.
• An Idempotency-Key header makes a retried paid call replay the first 200 instead of charging again (an answer larger than 1 MB is not replayed).

Paid call (JavaScript agent)

import { wrapFetchWithPayment } from "@x402/fetch";
import { x402Client } from "@x402/core/client";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

const client = new x402Client();
client.setSpendControls?.(false); // keep your own spending ceiling in code
registerExactEvmScheme(client, { signer: privateKeyToAccount(KEY) });
const payFetch = wrapFetchWithPayment(fetch, client);

const res = await payFetch("https://agent402.tools/api/a2a-card-validate", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "card": {
      "protocolVersion": "0.3.0",
      "name": "Sample Weather Agent",
      "description": "A sample A2A Agent Card served as a static example for card tooling. This describes a fictional weather agent, not a live A2A endpoint.",
      "url": "https://example.com/a2a/v1",
      "preferredTransport": "JSONRPC",
      "version": "1.0.0",
      "provider": {
        "organization": "Example Org",
        "url": "https://example.com"
      },
      "capabilities": {
        "streaming": true,
        "pushNotifications": false,
        "stateTransitionHistory": false
      },
      "defaultInputModes": [
        "application/json",
        "text/plain"
      ],
      "defaultOutputModes": [
        "application/json"
      ],
      "skills": [
        {
          "id": "get-forecast",
          "name": "Get weather forecast",
          "description": "Returns a city's 5-day forecast.",
          "tags": [
            "weather",
            "forecast"
          ],
          "examples": [
            "What is the weather in Paris this week?"
          ]
        }
      ]
    }
  }),
});

No wallet? Pay with compute

Fetch a challenge, solve the sha256 puzzle (16 leading zero bits, a fraction of a second of CPU), and resend with the X-Pow-Solution header:

import { createHash } from "node:crypto";
const lz = (b) => { let t = 0; for (const x of b) { if (!x) { t += 8; continue; } t += Math.clz32(x) - 24; break; } return t; };
const c = await (await fetch("https://agent402.tools/api/pow/challenge?slug=a2a-card-validate")).json();
let n = 0;
while (lz(createHash("sha256").update(c.challenge + ":" + n).digest()) < c.difficulty) n++;
await fetch("https://agent402.tools/api/a2a-card-validate", { method: "POST", headers: { "X-Pow-Solution": c.token + ":" + n, "Content-Type": "application/json" }, body: JSON.stringify({"card":{"protocolVersion":"0.3.0","name":"Sample Weather Agent","description":"A sample A2A Agent Card served as a static example for card tooling. This describes a fictional weather agent, not a live A2A endpoint.","url":"https://example.com/a2a/v1","preferredTransport":"JSONRPC","version":"1.0.0","provider":{"organization":"Example Org","url":"https://example.com"},"capabilities":{"streaming":true,"pushNotifications":false,"stateTransitionHistory":false},"defaultInputModes":["application/json","text/plain"],"defaultOutputModes":["application/json"],"skills":[{"id":"get-forecast","name":"Get weather forecast","description":"Returns a city's 5-day forecast.","tags":["weather","forecast"],"examples":["What is the weather in Paris this week?"]}]}}) });

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