x402 Payments: a facilitator for paid APIs and AI agents

import express from "express";
import { paymentMiddleware } from "@cryptoapis-io/x402-merchant-sdk/express";

const app = express();
const pay = paymentMiddleware({
  apiKey: process.env.CRYPTOAPIS_API_KEY,
  payTo: "0xYourBaseAddress",  // paid to you in USDC
});
const USDC_BASE = "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913";

// Unpaid calls get 402 Payment Required with the price: $0.01.
app.get("/api/forecast",
  pay({ network: "eip155:8453", asset: USDC_BASE, amount: "10000" }),
  (req, res) => res.json({ forecast: "sunny", payer: req.x402.payer }));

import { createX402Fetch } from "@cryptoapis-io/x402-buyer-sdk";
import { Wallet } from "ethers";

// The key is yours. It never leaves your process.
const wallet = new Wallet(process.env.PRIVATE_KEY);
const fetch402 = createX402Fetch({
  apiKey: process.env.CRYPTOAPIS_API_KEY,
  walletId: process.env.X402_WALLET_ID,  // has spending limits
  signer: { signTypedData: (td) => wallet.signTypedData(td.domain, td.types, td.message) },
});

// Pays the 402 challenge, then retries.
const res = await fetch402("https://api.example.com/api/forecast");

// Your MCP client config
{ "mcpServers": { "x402-pay": {
  "command": "npx",
  "args": ["-y", "@cryptoapis-io/mcp-x402-pay"],
  "env": {
    "X402_WALLET_ID": "YOUR_AGENT_WALLET_ID",
    "X402_ALLOWED_HOSTS": "api.example.com"
  }
} } }

// The agent can now call x402_pay (signs locally)
// and x402_discover (finds paid APIs and their prices).