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

> Source: <https://github.com/Evozim/m2mcent-sdk>
> Published: 2026-06-04 03:57:29+00:00

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 endpoint**Server responds** with`402 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 contract**Agent 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
```

| Parameter | Description | Required |
|---|---|---|
`rpcUrl` |
Base Mainnet RPC endpoint | ✅ |
`privateKey` |
Relayer wallet private key (for settlement) | ✅ |
`recipient` |
Treasury address to receive payments | ✅ |

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

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

| Parameter | Value |
|---|---|
Network |
Base Mainnet (Chain ID: 8453) |
USDC Contract |
`0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913` |
Escrow Contract |
`0xf3c3416A843d13C944554A54Ac274BB7fF264BcC` |
Settlement |
Atomic, sub-second finality |

Perfect for [Model Context Protocol](https://modelcontextprotocol.io) servers:

``` python
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](https://github.com/Evozim/m2mcent-sdk)