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Required Software

All examples require Node.js 18.17.0 or higher and npm 9.0.0 or higher.Check your versions:
node --version  # Should be v18.17.0 or higher
npm --version   # Should be 9.0.0 or higher
Install or update Node.js:
  • macOS/Linux: Use nvm 
    nvm install 18
nvm use 18
  • Windows: Download from nodejs.org
Required to clone the repository:
git --version
Install Git from git-scm.com if needed.
Recommended editors:
  • VS Code with TypeScript extensions
  • WebStorm or other JetBrains IDEs
  • Cursor for AI-assisted development

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Crossmint API Key

Some examples (particularly those using Crossmint smart wallets) require a Crossmint API key.
1

Sign up for Crossmint

Visit the Crossmint Console and create an account.
2

Get your API key

In the console, navigate to API Keys and create a new key for development.
Keep your API key secret. Never commit it to version control or share it publicly.
3

Configure environment

Add your API key to the .env file in the demo you’re running:
.env
CROSSMINT_API_KEY=your_api_key_here
The basic demos (ping, weather) don’t require a Crossmint API key. Start with those if you want to explore without signing up.

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Blockchain Prerequisites

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Testnet USDC Tokens

All demos use testnet USDC on either Base Sepolia or Solana Devnet. You’ll need testnet tokens to:
  • Make payments as a client/agent
  • Receive payments as a service provider
  • Test settlement verification
1

Get Base Sepolia USDC

Use the Circle testnet faucet:
  1. Visit faucet.circle.com
  2. Select Base Sepolia network
  3. Enter your wallet address
  4. Request testnet USDC (you’ll receive ~10 USDC)
You can request tokens once per day per address.
2

Get Solana Devnet USDC (if needed)

For Solana demos, use the Circle faucet:
  1. Visit faucet.circle.com
  2. Select Solana Devnet network
  3. Enter your Solana wallet address
  4. Request testnet USDC
3

Verify your balance

For Base Sepolia, check your balance on Basescan Sepolia.For Solana, use Solana Explorer (Devnet).

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Wallet Setup

For EVM-based demos, you need a wallet on Base Sepolia:Option 1: MetaMask
  1. Install MetaMask
  2. Add Base Sepolia network:
    • Network Name: Base Sepolia
    • RPC URL: https://sepolia.base.org
    • Chain ID: 84532
    • Currency Symbol: ETH
    • Block Explorer: https://sepolia.basescan.org
  3. Get testnet ETH from Base Sepolia faucet for gas
Option 2: Private Key Generate a new wallet for testing:
# Using cast (from Foundry)
cast wallet new

# Or using Node.js
node -e "console.log(require('ethers').Wallet.createRandom().privateKey)"
Only use test wallets with testnet tokens. Never use your main wallet’s private key.

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Understanding Key Terms

Before diving into the demos, familiarize yourself with these concepts:
x402 is an HTTP payment protocol using the 402 Payment Required status code.
  • Server returns 402 with payment requirements when a resource needs payment
  • Client generates a payment authorization header (X-PAYMENT)
  • Server verifies the payment and grants access
Learn more in x402 Protocol Concepts
A2A is a protocol for AI agents to communicate and transact autonomously.
  • Agents discover each other’s capabilities and pricing
  • Payments are made programmatically without human intervention
  • Enables agent-to-agent marketplaces and service networks
Learn more in A2A Payments
An EOA is a traditional blockchain wallet controlled by a private key.
  • User has full control via private key
  • Requires gas tokens (ETH, SOL) for transactions
  • Compatible with all standard wallets (MetaMask, Phantom, etc.)
Most basic demos use EOA wallets for simplicity.
Smart wallets (also called smart contract wallets) are programmable wallets.
  • Can execute complex logic (spending limits, multi-sig, etc.)
  • Crossmint smart wallets support gasless transactions
  • Enable features like email-based recovery and session keys
Learn more in Smart Wallets Concepts
MCP is a standard for integrating tools with AI models.
  • Allows AI agents to discover and use external tools
  • Payment-gated MCP tools enable autonomous agent economies
  • Used in advanced demos like events-concierge
Learn more at modelcontextprotocol.org
USDC (USD Coin) is a stablecoin pegged 1:1 to the US Dollar.
  • All demos use USDC for payments (not ETH or SOL)
  • Testnet USDC has no real value and is free from faucets
  • Production systems use mainnet USDC for real payments
Token addresses:
  • Base Sepolia: 0x036CbD53842c5426634e7929541eC2318f3dCF7e
  • Solana Devnet: 4zMMC9srt5Ri5X14GAgXhaHii3GnPAEERYPJgZJDncDU

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Development Tools (Optional)

These tools can enhance your development experience:

Foundry

EVM development toolkit with cast for wallet operations

Solana CLI

Command-line tools for Solana development

Thunder Client

VS Code extension for testing HTTP endpoints

Postman

API testing tool with support for custom headers

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Verification Checklist

Before starting the demos, ensure you have:
1

Software installed

  • Node.js 18.17.0+
  • npm 9.0.0+
  • Git
2

Accounts created

  • Crossmint account (optional for basic demos)
  • Wallet on Base Sepolia or Solana Devnet
3

Tokens acquired

  • Testnet USDC from Circle faucet
  • Testnet ETH or SOL for gas (if using EOA wallets)
4

Ready to code

  • Repository cloned: git clone https://github.com/crossmint/crossmint-agentic-finance.git
  • Environment variables configured

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Next Steps

Quick Start

Run your first paywall server in 5 minutes

x402 Protocol

Learn how the payment protocol works

HTTP Paywalls

Build payment-protected API endpoints

Agent-to-Agent

Create autonomous payment agents
Need help? Join the Crossmint Discord or check the GitHub discussions.

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