x402

x402 — HTTP Payment Protocol

Overview

x402 is an open payment protocol from Coinbase that revives the HTTP 402 (Payment Required) status code for instant, automatic stablecoin micropayments. It enables APIs and services to be monetized natively over HTTP — no accounts, sessions, or traditional payment processors required. Both human clients and AI agents can pay programmatically.

How It Works

Client                          Server                      Facilitator
  │                               │                             │
  │── GET /weather ──────────────►│                             │
  │◄── 402 Payment Required ─────│                             │
  │    (price, payTo, network)    │                             │
  │                               │                             │
  │── sign payment ──────────────►│                             │
  │   (PAYMENT-SIGNATURE header)  │── verify + settle ────────►│
  │                               │◄── confirmation ────────────│
  │◄── 200 OK (content) ─────────│                             │

Server Middleware

Express (TypeScript)

import { paymentMiddleware, x402ResourceServer } from "@x402/express";
import { ExactEvmScheme } from "@x402/evm/exact/server";
import { HTTPFacilitatorClient } from "@x402/core/server";

const resourceServer = new x402ResourceServer(
  new HTTPFacilitatorClient({ url: "https://x402.org/facilitator" })
);
resourceServer.register("eip155:84532", new ExactEvmScheme());

app.use(paymentMiddleware(
  {
    "GET /weather": {
      accepts: {
        scheme: "exact",
        price: "$0.001",
        network: "eip155:84532",
        payTo: "0xYourAddress",
      },
    },
  },
  resourceServer,
));

Flask (Python)

from flask import Flask
from x402.flask.middleware import PaymentMiddleware

app = Flask(__name__)
payment_middleware = PaymentMiddleware(app)

payment_middleware.add(
    path="/weather",
    price="$0.001",
    pay_to_address="0xYourAddress",
    network="base-sepolia",
)

@app.route("/weather")
def get_weather():
    return {"report": {"weather": "sunny", "temperature": 70}}