Show HN: X402-express. Pay-per-call HTTP 402 middleware for AI agents on Base L2

Ultra-lightweight x402 payment interceptor for AI Agents and MCP Servers. Monetize any API in 3 lines of code.

npm install m2mcent-sdk
js
import { X402Handler } from 'm2mcent-sdk';

const x402 = new X402Handler({
  rpcUrl: 'https://mainnet.base.org',
  privateKey: process.env.RELAYER_PRIVATE_KEY!,
  recipient: process.env.TREASURY_ADDRESS!
});

// Protect any Express endpoint with a USDC paywall
app.post('/api/analyze', x402.requirePayment("100000"), (req, res) => {
  res.json({ result: "Premium analysis complete", receipt: req.paymentTx });
});

M2MCent implements the x402 Payment Protocol — a machine-native payment standard inspired by HTTP 402:

Agent requests a protected endpointServer responds with402 Payment Required

• payment metadata (Base64 encoded)Agent signs an EIP-712 typed data authorization (gasless for the payer)Server settles atomically on-chain via the M2MCent Escrow contractAgent receives the premium response + transaction receipt

Agent ──► API Server ──► 402 + metadata
Agent ◄── signs EIP-712 authorization
Agent ──► API Server + Payment-Signature header
          └──► Escrow.settle() on Base L2
Agent ◄── Premium Response + tx hash

Non-custodial: Funds flow directly from payer → treasury via on-chain escrow** Gasless for payers**: Uses EIP-3009transferWithAuthorization

(USDC native)Zero-Leak: No agent data is retained after settlement** Atomic**: Payment and service delivery happen in a single request cycle

Perfect for Model Context Protocol servers:

import express from 'express';
import { X402Handler } from 'm2mcent-sdk';

const app = express();
const x402 = new X402Handler({
  rpcUrl: process.env.BASE_RPC_URL!,
  privateKey: process.env.RELAYER_PRIVATE_KEY!,
  recipient: process.env.TREASURY_ADDRESS!
});

// Any MCP tool endpoint becomes monetizable
app.post('/api/tools/analyze', x402.requirePayment("50000"), async (req, res) => {
  const result = await runMCPTool(req.body);
  res.json({ ...result, paymentTx: req.paymentTx });
});

M2MCent powers 100+ production MCP servers on Base Mainnet, processing real USDC micro-payments for AI-to-AI commerce.

MIT © M2MCent