JSON Schema validate

Validate a JSON document against a JSON Schema (draft-07 subset) and get the list of violations. 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.

Input

Field	Type	Description
data *	any	the JSON value to check (any type)
schema *	object	a JSON Schema (draft-07 subset)

Example output

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

Try it — see the 402 challenge (free)

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}}}}'

The response is HTTP 402 Payment Required with exact payment requirements. Any x402 v2 client pays automatically and retries:

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();
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

This is a pure-CPU tool, so an agent without a wallet can pay with proof-of-work instead of USDC: fetch a challenge, solve the sha256 puzzle (16 leading zero bits — a fraction of a second of CPU, no money, no AI tokens), 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}}}}) });

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