QR code

Generate a QR code PNG from any text or URL. ?text=…&size=256 (128-1024). Send GET /api/qr with the required field text and pay $0.001 per call over x402 or MPP, or call it free by solving a proof-of-work challenge. It returns raw bytes, not JSON, with Content-Type image/png.

Try in playground →

Parameters

Example request

curl -i "https://agent402.tools/api/qr?text=https%3A%2F%2Fagent402.tools&size=256"

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

Example response

A 200 carries raw bytes, not JSON, with Content-Type image/png: the file itself.

From an MCP client

catalog.call {
  "slug": "qr",
  "params": {
    "text": "https://agent402.tools",
    "size": "256"
  }
}

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

Errors and behavior

• text is 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 canceled 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 POST with a JSON body to /api/qr is served as this GET, with the body as the input.
• An Idempotency-Key header does not replay this tool's answer: the replay cache holds JSON answers only, so a retried paid call runs and is charged again.

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?.({ maxAmountPerPayment: "$0.001" }); // refuse any quote above this tool's price
registerExactEvmScheme(client, { signer: privateKeyToAccount(KEY) });
const payFetch = wrapFetchWithPayment(fetch, client);

const res = await payFetch("https://agent402.tools/api/qr?text=https%3A%2F%2Fagent402.tools&size=256");

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=qr")).json();
let n = 0;
while (lz(createHash("sha256").update(c.challenge + ":" + n).digest()) < c.difficulty) n++;
await fetch("https://agent402.tools/api/qr?text=https%3A%2F%2Fagent402.tools&size=256", { method: "GET", headers: { "X-Pow-Solution": c.token + ":" + n } });

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