JSON Schema infer

Infer a draft-07 JSON Schema from sample JSON document(s). Send one sample as json, or several as samples. Heuristic merge rules: required = keys present in every sample, conflicting types become a type union, integer widens to number, and string formats (date-time, date, email, uri, uuid) are detected from values. Complements json-validate.

Input

Field	Type	Description
json	any	a sample JSON document (object or JSON string)
samples	array	alternative: 1-50 sample documents merged into one schema

Example output

{
  "schema": {
    "$schema": "http://json-schema.org/draft-07/schema#",
    "type": "object",
    "properties": {
      "name": {
        "type": "string"
      },
      "age": {
        "type": "integer"
      }
    },
    "required": [
      "name",
      "age"
    ]
  },
  "samples": 1
}

Try it — see the 402 challenge (free)

curl -i -X POST https://agent402.tools/api/json-schema-infer \
  -H "Content-Type: application/json" \
  -d '{"json":{"name":"Ada","age":36,"active":true,"tags":["pioneer"],"joined":"1843-10-18"}}'

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-schema-infer", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "json": {
      "name": "Ada",
      "age": 36,
      "active": true,
      "tags": [
        "pioneer"
      ],
      "joined": "1843-10-18"
    }
  }),
});

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-schema-infer")).json();
let n = 0;
while (lz(createHash("sha256").update(c.challenge + ":" + n).digest()) < c.difficulty) n++;
await fetch("https://agent402.tools/api/json-schema-infer", { method: "POST", headers: { "X-Pow-Solution": c.token + ":" + n, "Content-Type": "application/json" }, body: JSON.stringify({"json":{"name":"Ada","age":36,"active":true,"tags":["pioneer"],"joined":"1843-10-18"}}) });

Part of these workflows

This tool is one step in a curated multi-tool workflow — agents can fetch the whole sequence as an MCP prompt or call https://agent402.tools/api/skill-packs/{slug}/prompt.

• 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.

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