JSON Schema validate

Validate a JSON document against a JSON Schema (draft-07 subset) and get the list of violations. Send POST /api/json-validate with the required fields data and schema and pay $0.001 per call over x402 or MPP, or call it free by solving a proof-of-work challenge. It returns a JSON object with valid and errors.

Supports type, required, properties, items, enum, const, min/max, length, pattern, format, anyOf/allOf/oneOf/not, additionalProperties. Deterministic - check an agent's structured output before you trust it.

Category: Live public data · Tags: json-schema validate structured-output draft-07

TRY IN PLAYGROUND →

Parameters

Example request

curl -i -X POST https://agent402.tools/api/json-validate \
  -H "Content-Type: application/json" \
  -d '{"data":{"name":"x","age":3},"schema":{"type":"object","required":["name"],"properties":{"name":{"type":"string"},"age":{"type":"integer","minimum":0}}}}'

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

Example response

{
  "valid": true,
  "errors": []
}

From an MCP client

catalog.call {
  "slug": "json-validate",
  "params": {
    "data": {
      "name": "x",
      "age": 3
    },
    "schema": {
      "type": "object",
      "required": [
        "name"
      ],
      "properties": {
        "name": {
          "type": "string"
        },
        "age": {
          "type": "integer",
          "minimum": 0
        }
      }
    }
  }
}

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

Errors and behavior

• data and schema are 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/json-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/json-validate", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "data": {
      "name": "x",
      "age": 3
    },
    "schema": {
      "type": "object",
      "required": [
        "name"
      ],
      "properties": {
        "name": {
          "type": "string"
        },
        "age": {
          "type": "integer",
          "minimum": 0
        }
      }
    }
  }),
});

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=json-validate")).json();
let n = 0;
while (lz(createHash("sha256").update(c.challenge + ":" + n).digest()) < c.difficulty) n++;
await fetch("https://agent402.tools/api/json-validate", { method: "POST", headers: { "X-Pow-Solution": c.token + ":" + n, "Content-Type": "application/json" }, body: JSON.stringify({"data":{"name":"x","age":3},"schema":{"type":"object","required":["name"],"properties":{"name":{"type":"string"},"age":{"type":"integer","minimum":0}}}}) });

Part of these workflows

JSON Schema validate is one step in these 3 skill packs, each sold as a single call:

• Schema guard - Contract-test a JSON payload in one call: validate it against your schema, infer the schema the payload actually implies, diff the two to expose drift, and return a normalized pretty-print.
• JSON pipeline - Validate, pretty-print, and convert JSON to CSV in one pass - the complete JSON processing workflow.
• Webhook secure intake - The production ingest path for every incoming webhook: verify the provider signature (GitHub / Stripe / Shopify / Slack, constant-time, replay-window enforced), schema-validate the now-trusted body against the provider envelope, fingerprint the raw bytes for redelivery dedup, normalize the event timestamp to UTC + epoch, and redact PII before anything hits a log. Five pure-CPU tools - the accept-or-reject gate, run on every event.

Related tools