Skill: Schema guard

Bundled execution of the Schema guard workflow — 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. One x402 payment runs 4 underlying tools (json-validate, json-schema-infer, json-diff, json-format); partial-success per step.

Input

Field	Type	Description
payload *	string	The JSON payload to check (as a JSON string)
schema	string	The expected JSON Schema (as a JSON string; defaults to none)

Example output

{
  "pack": "schema-guard",
  "args": {
    "payload": "{\"id\":1,\"name\":\"Ada\"}",
    "schema": "{\"type\":\"object\",\"required\":[\"id\"]}"
  },
  "steps": [
    {
      "slug": "json-validate",
      "ok": true,
      "result": {}
    },
    {
      "slug": "json-schema-infer",
      "ok": true,
      "result": {}
    },
    {
      "slug": "json-diff",
      "ok": true,
      "result": {}
    },
    {
      "slug": "json-format",
      "ok": true,
      "result": {}
    }
  ],
  "summary": "4/4 steps succeeded"
}

Try it — see the 402 challenge (free)

curl -i -X POST https://agent402.tools/api/skill/schema-guard \
  -H "Content-Type: application/json" \
  -d '{"payload":"{\"id\":1,\"name\":\"Ada\"}","schema":"{\"type\":\"object\",\"required\":[\"id\"]}"}'

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/skill/schema-guard", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "payload": "{\"id\":1,\"name\":\"Ada\"}",
    "schema": "{\"type\":\"object\",\"required\":[\"id\"]}"
  }),
});

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=skill-schema-guard")).json();
let n = 0;
while (lz(createHash("sha256").update(c.challenge + ":" + n).digest()) < c.difficulty) n++;
await fetch("https://agent402.tools/api/skill/schema-guard", { method: "POST", headers: { "X-Pow-Solution": c.token + ":" + n, "Content-Type": "application/json" }, body: JSON.stringify({"payload":"{\"id\":1,\"name\":\"Ada\"}","schema":"{\"type\":\"object\",\"required\":[\"id\"]}"}) });

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