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Baazar Quickstart (JavaScript Demo)

A simple demonstration of how to build a pay-to-play web application using the Coinbase Developer Platform (CDP) and X402 protocol. This example shows how to integrate microtransactions into an Express.js app using x402-express and how to consume those APIs securely using x402-fetch.

Features

This demo application demonstrates:

  1. CDP SDK Integration – Setting up a CDP account using the Coinbase SDK
  2. Payment Middleware – Using x402-express to monetize API endpoints
  3. X402 Payments – Handling paid fetch requests via x402-fetch
  4. Game Logic – Building a simple Rock–Paper–Scissors game with payment enforcement
  5. Catalog Discovery – Listing available X402 APIs from the CDP catalog

Prerequisites

  • Node.js 18 or higher
  • pnpm package manager
  • A Coinbase Developer Platform (CDP) account
  • Access to Base Sepolia testnet

Installation

  1. Install dependencies:
pnpm install
  1. Create a .env file in the root directory and include your CDP credentials:
CDP_API_KEY_ID=your_api_key_id_here
CDP_API_KEY_SECRET=your_api_key_secret_here
CDP_WALLET_SECRET=your_wallet_secret_here

Getting CDP Credentials

  1. Visit the CDP Portal
  2. Create a new project or select an existing one
  3. Navigate to Settings > API Keys
  4. Click Create API Key
  5. Download the credentials and place them in your .env file

Usage

You can run both the seller (API server) and buyer (client) parts of the demo.

1. Start the Payment-Enabled Server

node index.js

This server exposes a single paid endpoint:

  • POST /rps/play

    • Price: $0.001 (Base Sepolia testnet)
    • Description: “Pay to play Rock–Paper–Scissors”
    • Input: { "move": "rock" | "paper" | "scissors" }
    • Output: { "serverMove": "...", "userMove": "...", "outcome": "win|lose|draw" }

Example console output:

Server listening at http://localhost:4021

2. Run the Buyer Script

node buyer.js

The script uses:

  • @coinbase/cdp-sdk to load your CDP account
  • x402-fetch to make paid requests
  • decodeXPaymentResponse to read payment receipts

Example output:

Game result: { serverMove: 'rock', userMove: 'paper', outcome: 'win' }
Payment receipt: {...}

3. (Optional) List Publicly Discoverable APIs

node list-catalog.js

This will fetch and print all X402 resources listed in the CDP discovery catalog.

Security Best Practices

  1. Never commit your .env file – Add it to .gitignore
  2. Use testnets – Test on Base Sepolia before mainnet
  3. Rotate keys regularly – Ensure credential hygiene
  4. Validate payment receipts – Always verify payment headers before processing