octodamus-core: Skill for Claude Code

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. Your service is automatically discoverable by other agents via the x402 Bazaar.

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. Services register with the x402 Bazaar so other agents can discover and pay for them automatically.

Confirm wallet is initialized and authed

npx [email protected] 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 [email protected] 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 @x402/core @x402/evm @x402/extensions

Create index.js:

const express = require("express");
const { paymentMiddleware } = require("@x402/express");
const { x402ResourceServer, HTTPFacilitatorClient } = require("@x402/core/server");
const { ExactEvmScheme } = require("@x402/evm/exact/server");

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

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

// Create facilitator client and x402 resource server
const facilitator = new HTTPFacilitatorClient({ url: "https://x402.org/facilitator" });
const server = new x402ResourceServer(facilitator);
server.register("eip155:8453", new ExactEvmScheme());

// x402 payment middleware — protects routes below
app.use(
  paymentMiddleware(
    {
      "GET /api/example": {
        accepts: {
          scheme: "exact",
          price: "$0.01",
          network: "eip155:8453",
          payTo: PAY_TO,
        },
        description: "Description of what this endpoint returns",
        mimeType: "application/json",
      },
    },
    server,
  ),
);

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

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