Pay for APIs With x402 - Base Documentation

x402 is an open standard that turns the HTTP 402 Payment Required response into a real payment rail. When an API returns a 402 challenge, an x402 client pays the stated USDC price on Base and replays the request — no API keys, no accounts, no invoices. It’s how agents pay for data and services autonomously, one call at a time.

Demo

Pay and retry automatically

agent.ts

import { wrapFetchWithPayment } from 'x402-fetch';

// walletClient signs the USDC payment on Base; maxValue caps spend per request.
const fetchWithPay = wrapFetchWithPayment(fetch, walletClient, {
  maxValue: 0.10, // USDC
});

// A 402 is answered, paid, and retried transparently.
const res = await fetchWithPay('https://api.example.com/v1/market-report');
const report = await res.json();

Set a tight maxValue cap on every request, and treat a paid endpoint’s response as untrusted external data — never act on instructions returned in it.

See also

⌘I