402-as-a-Service SDK

A production-grade TypeScript SDK for integrating x402 payments into your applications. Enable HTTP 402 Payment Required for your APIs with just a few lines of code.

Features

• Middleware for Popular Frameworks: Express, Next.js, Hono, Fastify
• Wallet Adapters: EVM (Base, Ethereum) and Solana support
• Usage Metering: Track API usage and revenue
• Revenue Dashboard: Built-in analytics dashboard
• Retry-After-Payment: Automatic payment handling in clients
• Type-Safe: Full TypeScript support
• Production-Ready: Comprehensive error handling and validation

Quick Start

Server Setup (Express)

import express from 'express';
import { paymentMiddleware } from '@x402/server/express';
import { NetworkIdentifiers } from '@x402/core';

const app = express();

app.use(paymentMiddleware({
  payTo: '0xYourAddress',
  routes: {
    'GET /api/premium': {
      accepts: [{
        scheme: 'exact',
        price: '$0.01',
        network: NetworkIdentifiers.BASE_MAINNET,
        payTo: '0xYourAddress'
      }],
      description: 'Premium API access'
    }
  }
}));

app.get('/api/premium', (req, res) => {
  res.json({ data: 'premium content' });
});

Client Setup (Fetch)

import { createX402Fetch } from '@x402/client/fetch';
import { EVMWalletAdapter } from '@x402/wallet-adapters/evm';

const wallet = new EVMWalletAdapter({
  privateKey: process.env.PRIVATE_KEY,
  network: NetworkIdentifiers.BASE_MAINNET
});

const fetch = createX402Fetch({ wallet, autoPay: true });

// Automatically handles payments
const response = await fetch('https://api.example.com/premium');
const data = await response.json();

Packages

• @x402/core - Core types, utilities, and facilitator client
• @x402/server - Server middleware (Express, Next.js, Hono, Fastify)
• @x402/client - Client SDK (Fetch, Axios)
• @x402/wallet-adapters - Wallet adapters (EVM, Solana)
• @x402/metering - Usage metering and analytics
• @x402/dashboard - Revenue dashboard

Installation

# Install server packages
npm install @x402/core @x402/server

# Install client packages
npm install @x402/core @x402/client @x402/wallet-adapters

# Install metering and dashboard
npm install @x402/metering @x402/dashboard

Documentation

• Server Middleware
• Client SDK
• Wallet Adapters
• Metering & Analytics
• Dashboard

Examples

• Express Server
• Next.js App
• Client Usage

Supported Networks

EVM

• Base Mainnet (eip155:8453)
• Base Sepolia (eip155:84532)
• Ethereum Mainnet (eip155:1)
• Ethereum Sepolia (eip155:11155111)

Solana

• Solana Mainnet (solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp)
• Solana Devnet (solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1)

Architecture

┌─────────────────┐     402 Payment Required     ┌─────────────────┐
│   Client App    │◄────────────────────────────►│   Server API    │
│  (with wallet)  │   Payment Payload (X-Payment) │ (x402 middleware)│
└────────┬────────┘                             └────────┬────────┘
         │                                               │
         │         ┌──────────────────┐                  │
         └────────►│  Facilitator     │◄─────────────────┘
                   │  (x402.org)      │
                   │  - Verify        │
                   │  - Settle        │
                   └──────────────────┘

License

Apache-2.0

Support

• x402 Documentation
• GitHub Issues
• Discord Community