setup-x402-server

Add x402 Paywall to Your Server

Protect any Express endpoint with x402 payments. Users pay USDC to access your API.

The test client below is an independent @dexterai/x402 SDK integration. It is not the OpenDexter MCP runtime and does not inherit OpenDexter identity, authority, limits, or receipts. Never substitute it for a blocked OpenDexter account-bound operation.

Steps

1. Install the SDK:

npm install @dexterai/[email protected] @dexterai/[email protected]

1. Add the middleware to any Express route:

import express from 'express';
import { x402Middleware } from '@dexterai/x402/server';

const app = express();

app.get('/api/premium-data',
  x402Middleware({
    payTo: 'YOUR_SOLANA_ADDRESS', // Replace with your wallet address
    amount: '0.01',               // $0.01 per request
  }),
  (req, res) => {
    // This only runs after successful payment
    res.json({
      data: 'premium content',
      payer: req.x402?.payer,
      transaction: req.x402?.transaction,
    });
  }
);

app.listen(3000);

1. Test with curl — first request gets a 402:

curl -i http://localhost:3000/api/premium-data
# HTTP/1.1 402 Payment Required
# PAYMENT-REQUIRED: eyJ4NDAy...

1. Test with a funded x402 client:

import { createKeypairWallet, payAndFetch } from '@dexterai/x402/client';

const solana = await createKeypairWallet(process.env.SOLANA_PRIVATE_KEY!);

const paid = await payAndFetch(
  'http://localhost:3000/api/premium-data',
  { method: 'GET' },
  { solana },
  { maxAmountAtomic: '10000', solanaRpcUrl: process.env.SOLANA_RPC_URL },
);
if (!paid.ok) throw new Error(`${paid.reason}: ${paid.detail ?? ''}`);
if (!paid.response) throw new Error('Payment settled without a merchant response');
const res = paid.response;
console.log(await res.json());
// { data: "premium content", payer: "2SB3V...", transaction: "5xK9..." }

Options

• Dynamic pricing: Use getAmount: (req) => calculatePrice(req.body) for request-dependent pricing.
• EVM chains: Set network: 'eip155:8453' for Base instead of Solana.
• Multi-chain: Pass a network array and a per-network payTo map.