x402 Protocol — USDC Micropayments for AI Agents & LLM APIs

npm install @xpaylabs/x402

import { pay } from '@xpaylabs/x402';

const response = await pay('https://api.example.com/weather', {
  amount: '0.001',       // USDC amount
  network: 'base-sepolia',
  privateKey: '0x...',   // buyer's EVM private key
});

console.log(response.data);     // response body
console.log(response.paymentId); // on-chain tx hash

import { XPayClient } from '@xpaylabs/x402';

const client = new XPayClient({
  privateKey: '0x...',
  network: 'base-sepolia',
  facilitatorUrl: 'https://x402-facilitator-testnet.vercel.app/api',
});

const res1 = await client.request('https://api.example.com/weather', {
  amount: '0.001',
});
const res2 = await client.request('https://api.example.com/weather', {
  amount: '0.001',
});

import { extractPaymentId } from '@xpaylabs/x402';

const paymentId = extractPaymentId(response.headers);
console.log(paymentId); // "0xabc...123"

npm install @x402/express

import express from 'express';
import { x402Middleware } from '@x402/express';

const app = express();

app.use(x402Middleware({
  network: 'base-sepolia',
  facilitatorUrl: 'https://x402-facilitator-testnet.vercel.app/api',
  evmAddress: '0x...',       // seller's USDC receiving address
}));

// Paid route — client must include valid x402 payment
app.get('/api/generate', (req, res) => {
  // req.x402 contains decoded payment info
  res.json({ result: 'llm response', paymentId: req.x402.paymentId });
});

// Public route — no payment required
app.get('/health', (req, res) => {
  res.json({ status: 'ok' });
});

AI Agent (buyer)                    AI API (seller)
      │                                   │
      │  1. POST /api/generate            │
      │     (no payment yet)              │
      │                                   │
      │  2. 402 Payment Required          │
      │     { amount: "0.001" }           │
      │                                   │
      │  3. Submit USDC Transfer (on-chain)│
      │     via x402 facilitator          │
      │                                   │
      │  4. retry with x402 auth header   │
      │                                   │
      │  5. 200 OK + response             │
      │     (paymentId in headers)        │