Reference implementations: Crossmint Agentic Finance

Reference implementations showing AI agents making autonomous blockchain payments using Crossmint wallets.

Prerequisites

Required:

• Node.js 18.17.0+
• npm 9.0.0+
• Crossmint API key - Get one

For blockchain interactions:

• Testnet USDC - Circle faucet
• Basic understanding of smart contracts and wallets

Glossary:

• x402: HTTP payment protocol using 402 Payment Required status code
• A2A: Agent-to-Agent - protocol for AI agents to communicate and transact
• EOA: Externally Owned Account - traditional wallet controlled by private key
• MCP: Model Context Protocol - standard for AI tool integration

Quick Start

Simplest demo:

# Clone repository
git clone https://github.com/crossmint/crossmint-agentic-finance.git
cd crossmint-agentic-finance

# Run basic x402 paywall
cd ping
cp .env.example .env
# Edit .env: Set PAY_TO to your address
npm install
npm run dev

# Test in another terminal
curl -i -H "Accept: application/json" http://localhost:3000/ping
# Returns 402 Payment Required with payment details

Learn the payment flow: See ping/README.md for generating payment headers and testing settlements.

Demos by Use Case

HTTP Paywalls (Start Here)

Minimal servers requiring USDC payment to access endpoints.

Demo	Chain	Description	Complexity
ping	Base Sepolia	Express server, /ping endpoint requires payment	Beginner
weather	Base Sepolia	Express server, /weather?city=X endpoint requires payment	Beginner
ping-crossmint	Base Sepolia	React + Express with Crossmint smart wallet UI integration	Intermediate
pingpong-solana-x402	Solana Devnet	React + Cloudflare Worker, Solana USDC via facilitator	Intermediate

Start with: ping for pure backend, ping-crossmint for full-stack

Agent-to-Agent Payments

Autonomous agents paying each other for services and tool access.

Demo	Architecture	Description	Complexity
hello-eoa-a2a	Client/Server	Minimal A2A with EOA wallets, EIP-3009 authorization	Beginner
hello-crossmint-wallets-a2a	React + Express	A2A demo with Crossmint SDK, direct-transfer verification	Intermediate
send-tweet	Agent Service	Twitter posting agent, requires USDC payment per tweet	Intermediate
events-concierge	Durable Objects	MCP-based event RSVP with autonomous payments	Advanced
cloudflare-agents	Cloudflare Workers	Agent-to-agent payments on Cloudflare edge	Advanced

Start with: hello-eoa-a2a for basics, events-concierge for production patterns

Production/Real World Examples

Real-world implementations with advanced features.

Demo	Type	Description	Complexity
worldstore-agent↗	XMTP Agent	Amazon purchases via AI chat with gasless USDC payments on Base	Advanced
x402-ad-agent↗	Bidding System	Claude-powered agents competing for ad space with autonomous payments	Advanced
events-concierge	agents based calendar slot booking system	event RSVP with payments	Advanced