JSON query

Extract a value from JSON by dot/bracket path, e.g. "items[2].name".

Input

Field	Type	Description
json *	any	JSON value (or a JSON string of one)
path *	string	Path like "a.b[0].c"

Example output

{
  "found": true,
  "value": "b"
}

Try it - see the 402 challenge (free)

curl -i -X POST https://agent402.tools/api/json-query \
  -H "Content-Type: application/json" \
  -d '{"json":{"items":[{"name":"a"},{"name":"b"}]},"path":"items[1].name"}'

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-query", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "json": {
      "items": [
        {
          "name": "a"
        },
        {
          "name": "b"
        }
      ]
    },
    "path": "items[1].name"
  }),
});

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-query")).json();
let n = 0;
while (lz(createHash("sha256").update(c.challenge + ":" + n).digest()) < c.difficulty) n++;
await fetch("https://agent402.tools/api/json-query", { method: "POST", headers: { "X-Pow-Solution": c.token + ":" + n, "Content-Type": "application/json" }, body: JSON.stringify({"json":{"items":[{"name":"a"},{"name":"b"}]},"path":"items[1].name"}) });

Part of these workflows

This tool is one step in 2 curated multi-tool workflows - agents can fetch the whole sequence as an MCP prompt or call https://agent402.tools/api/skill-packs/{slug}/prompt.

• API investigation - Point at an unknown API endpoint and figure out how to use it: auth scheme, content type, version, rate limits, OpenAPI/Swagger spec discovery, and JSON response structure. The deterministic recon workflow before writing a single line of integration code.
• CSV profile - Hand the pack a CSV and get back a column-by-column profile: descriptive stats, outliers, pairwise correlations, and a baseline linear regression. The deterministic 'what's in this dataset?' workup before deciding what to actually model.

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