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The @delegare/x402 package lets merchants monetize API endpoints using the x402 protocol. It handles the 402 challenge and payment verification — settlement is handled by Delegare’s infrastructure on the Base blockchain.

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Installation

npm install @delegare/x402

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Quick Start

import express from 'express';
import { requireX402Payment } from '@delegare/x402';

const app = express();

app.get('/premium-data',
  requireX402Payment({
    price: '0.05',                  // 5 cents USDC per call
    payTo: '0xYourWalletAddress',   // Your Base wallet
  }),
  (req, res) => {
    res.json({ data: 'premium content' });
  }
);

app.listen(4000);
That’s it. Any AI agent using @delegare/sdk or the Delegare MCP tools will automatically resolve the 402 challenge and pay.

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How It Works

Agent → GET /premium-data → 402 Payment Required (x402 challenge)
Agent → GET /premium-data + X-DELEGARE-MANDATE header
     → Middleware forwards mandate to Delegare API
     → Delegare settles on Base via DelegareRouter contract
     → USDC arrives in your wallet
     → 200 OK + data
The middleware never touches private keys or on-chain logic. Delegare handles settlement; the Base blockchain handles custody; your wallet receives USDC directly.

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Configuration

requireX402Payment({
  // Required
  price: '0.05',                    // Decimal USDC (e.g. "0.05" = 5 cents)
  payTo: '0xYourWallet',            // Base wallet that receives payment

  // Optional
  testMode: true,                   // Use Base Sepolia (default: false)
  apiUrl: 'https://api.sandbox.delegare.dev/v1', // Sandbox API
  resource: '/api/premium-data',    // Override resource ID
  mimeType: 'application/json',     // Content type advertised in challenge
  maxTimeoutSeconds: 3600,          // Payment validity window
});

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Accessing Payment Context

After a successful payment, the middleware attaches metadata to the request: 
app.get('/premium-data',
  requireX402Payment({ price: '0.05', payTo: '0xYourWallet' }),
  (req, res) => {
    const payer = (req as any).x402Payer;        // Payer's wallet address
    const txHash = (req as any).x402Transaction;  // On-chain tx hash

    // You can verify the tx on BaseScan:
    // https://basescan.org/tx/{txHash}

    res.json({ data: '...', paidBy: payer });
  }
);
The X-PAYMENT-RESPONSE header is also set on the response, allowing the agent to confirm payment was settled.

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Testing with Sandbox

For development, use testnet mode: 
requireX402Payment({
  price: '0.01',
  payTo: '0xYourTestnetWallet',
  testMode: true,
  apiUrl: 'https://api.sandbox.delegare.dev/v1',
});
This uses Base Sepolia and testnet USDC — no real funds involved.

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TypeScript Types

The package exports all relevant types: 
import type {
  X402Options,         // Middleware config
  X402Requirement,     // Single entry in 402 challenge
  X402Challenge,       // Full 402 response body
  X402PaymentReceipt,  // Decoded X-PAYMENT-RESPONSE
} from '@delegare/x402';