USDCx Bridge

Bridge USDC to Stacks using ChatGPT. No contracts. No complexity. Just conversation.

The first conversational bridge interface built on ChatGPT's Apps SDK and Model Context Protocol.

What It Does

Talk to ChatGPT, connect your wallets (MetaMask + Leather), and bridge USDC between Ethereum and Stacks—all without leaving the chat interface.

Why It Exists

Bridging USDC to Stacks today requires manual smart contract calls, complex address encoding (c32 → bytes32), and waiting 15-60 minutes with zero visibility.

USDCx Bridge makes it as easy as describing what you want in plain English.

How It Works

1. Natural language - "Bridge 50 USDC to Stacks"
2. Widget appears - React component renders in ChatGPT
3. Connect wallets - MetaMask for Ethereum, Leather for Stacks
4. Sign & bridge - One click, you sign with your wallet
5. Track live - See confirmations and ETA in real-time

Features

• ✅ Conversational interface - No technical knowledge required
• ✅ Your wallets, your control - We never custody funds
• ✅ Live status tracking - Know exactly what's happening
• ✅ Built on official protocols - Circle xReserve + Stacks attestation
• ✅ Open source - Verify everything
• ✅ First MCP blockchain app - Sets the standard

Quick Start

1. Enable Developer Mode in ChatGPT settings

2. Create a custom app and add this MCP server:

https://usdcxbridge.fly.dev/mcp

3. Type in ChatGPT:

"Bridge USDC to Stacks"

That's it. The widget will appear and guide you through the rest.

Tech Stack

Backend

• @modelcontextprotocol/sdk - MCP server
• viem - Ethereum contract interactions
• @stacks/transactions - Stacks operations
• Node.js + TypeScript

Frontend (Widgets)

• React + TypeScript
• viem - Ethereum wallet connections
• @stacks/connect - Stacks wallet integration

Bridge Infrastructure

• Circle xReserve (Ethereum smart contracts)
• Stacks attestation service

Security

• ✅ You connect your own wallets
• ✅ You sign every transaction
• ✅ We never custody your funds
• ✅ We never access your private keys
• ✅ Uses official Circle xReserve protocol

Development

Prerequisites

• Node.js 18+
• npm or pnpm

Installation

# Clone repo
git clone https://github.com/yourusername/usdcx-bridge.git
cd usdcx-bridge

# Install dependencies
npm install

# Build everything (server + widgets)
npm run build

# Run MCP server locally (stdio mode)
npm start

# Run HTTP server (for ChatGPT integration)
npm run start:http

# Test with MCP inspector
npm test

Environment Variables

Create a .env file:

# Ethereum Network (mainnet or testnet)
ETHEREUM_NETWORK=testnet
ETHEREUM_RPC_URL=https://ethereum-sepolia.publicnode.com

# Stacks Network
STACKS_NETWORK=testnet

# Contract Addresses (Testnet)
XRESERVE_CONTRACT=0x008888878f94C0d87defdf0B07f46B93C1934442
USDC_CONTRACT=0x1c7D4B196Cb0C7B01d743Fbc6116a902379C7238
STACKS_USDCX_CONTRACT=ST1PQHQKV0RJXZFY1DGX8MNSNYVE3VGZJSRTPGZGM.usdcx-v1

# HTTP Server
PORT=3001
BASE_URL=http://localhost:3001

Project Structure

usdcx-bridge/
├── src/
│   ├── server/
│   │   ├── index.ts           # MCP server (stdio mode)
│   │   ├── http-server.ts     # HTTP wrapper for ChatGPT
│   │   └── lib/
│   │       ├── ethereum.ts    # Ethereum/xReserve logic
│   │       ├── stacks.ts      # Stacks/USDCx logic
│   │       └── helpers.ts     # Address encoding utilities
│   └── widgets/
│       ├── DepositWidget.tsx      # Ethereum → Stacks
│       ├── WithdrawalWidget.tsx   # Stacks → Ethereum
│       ├── StatusWidget.tsx       # Transaction tracking
│       └── hooks/
│           ├── useMetaMask.ts     # MetaMask integration
│           └── useLeather.ts      # Leather wallet integration
├── dist/                      # Built files
├── package.json
├── tsconfig.json
└── README.md

Architecture

ChatGPT
    ↓
MCP Server (tools: prepareDeposit, prepareWithdrawal, checkStatus)
    ↓
React Widgets (wallet connection + transaction signing)
    ↓
Smart Contracts (xReserve on Ethereum, usdcx-v1 on Stacks)

MCP Tools

The server exposes these tools to ChatGPT:

prepareDeposit

Prepares USDC → USDCx bridge transaction (Ethereum to Stacks)

Parameters:

• amount - Amount of USDC to bridge
• stacksRecipient - Destination Stacks address
• userEthereumAddress - User's Ethereum address

Returns: Widget URL for MetaMask signing

prepareWithdrawal

Prepares USDCx → USDC withdrawal transaction (Stacks to Ethereum)

Parameters:

• amount - Amount of USDCx to withdraw (minimum 4.80)
• ethereumRecipient - Destination Ethereum address
• stacksAddress - User's Stacks address

Returns: Widget URL for Leather signing

checkStatus

Checks transaction status on either chain

Parameters:

• txHash - Transaction hash
• chain - Either "ethereum" or "stacks"

Returns: Status widget with live updates

getBalances

Gets USDC and USDCx balances

Parameters:

• ethereumAddress (optional)
• stacksAddress (optional)

Returns: Balance information

healthCheck

Verifies bridge contracts are operational

Returns: System status

Deployment

Docker

# Build image
docker build -t usdcx-bridge .

# Run container
docker run -p 3001:3001 usdcx-bridge

Fly.io

# Install flyctl
curl -L https://fly.io/install.sh | sh

# Deploy
fly deploy

Manual

# Build
npm run build

# Start
NODE_ENV=production npm run start:http

Testing

Local Testing with MCP Inspector

npm test

This opens the MCP inspector for testing tools locally.

Test Deposit Flow

1. Get testnet USDC from Sepolia faucet
2. In ChatGPT: "Bridge 5 USDC to ST1PQHQKV0RJXZFY1DGX8MNSNYVE3VGZJSRTPGZGM"
3. Click widget link
4. Connect MetaMask
5. Approve USDC (if needed)
6. Sign bridge transaction
7. Wait ~15 minutes
8. Check USDCx balance on Stacks

Test Withdrawal Flow

1. Ensure you have USDCx on Stacks testnet
2. In ChatGPT: "Withdraw 5 USDCx to 0xYourEthereumAddress"
3. Click widget link
4. Connect Leather wallet
5. Sign burn transaction
6. Wait ~25-45 minutes
7. Check USDC balance on Ethereum

Troubleshooting

Widget not loading

• Check that npm run build completed successfully
• Verify HTTP server is running on correct port
• Check browser console for errors

MetaMask connection fails

• Install MetaMask extension
• Switch to Sepolia testnet
• Refresh page and try again

Leather connection fails

• Install Leather wallet
• Create/import Stacks wallet
• Ensure on testnet mode

Transaction stuck

• Check transaction on block explorer
• For Ethereum: https://sepolia.etherscan.io
• For Stacks: https://explorer.hiro.so (testnet)
• Bridge can take 15-60 minutes depending on attestation

Contributing

Contributions welcome! Please:

1. Fork the repo
2. Create a feature branch
3. Make your changes
4. Add tests
5. Submit a pull request

License

MIT License - see LICENSE file

Links

• Documentation: MCP Protocol Docs
• Circle xReserve: Official Docs
• Stacks USDCx: GitHub
• Report Issues: GitHub Issues

Acknowledgments

Built with:

• ChatGPT Apps SDK
• Model Context Protocol
• Circle's xReserve Protocol
• Stacks Blockchain
• Viem & wagmi
• React

Made with ❤️ for the Bitcoin & Ethereum ecosystems