Build an x402 Payment Server

Create an Express server that charges USDC for API access using the x402 payment protocol. Callers pay per-request in USDC on Base — no accounts, API keys, or subscriptions needed.

How It Works

x402 is an HTTP-native payment protocol. When a client hits a protected endpoint without paying, the server returns HTTP 402 with payment requirements. The client signs a USDC payment and retries with a payment header. The facilitator verifies and settles the payment, and the server returns the response.

Confirm wallet is initialized and authed

npx awal@latest status

If the wallet is not authenticated, refer to the authenticate-wallet skill.

Step 1: Get the Payment Address

Run this to get the wallet address that will receive payments:

npx awal@latest address

Use this address as the payTo value.

Step 2: Set Up the Project

mkdir x402-server && cd x402-server
npm init -y
npm install express x402-express

Create index.js:

const express = require("express");
const { paymentMiddleware } = require("x402-express");

const app = express();
app.use(express.json());

const PAY_TO = "<address from step 1>";

// x402 payment middleware — protects routes below
const payment = paymentMiddleware(PAY_TO, {
  "GET /api/example": {
    price: "$0.01",
    network: "base",
    config: {
      description: "Description of what this endpoint returns",
    },
  },
});

// Protected endpoint
app.get("/api/example", payment, (req, res) => {
  res.json({ data: "This costs $0.01 per request" });
});

app.listen(3000, () => console.log("Server running on port 3000"));

Step 3: Run It

node index.js

Test with curl — you should get a 402 response with payment requirements:

curl -i http://localhost:3000/api/example

API Reference

paymentMiddleware(payTo, routes, facilitator?)

Creates Express middleware that enforces x402 payments.

Route Config

Each key in the routes object is "METHOD /path". The value is either a price string or a config object:

// Simple — just a price
{ "GET /api/data": "$0.05" }