hardhat-metamask-connector

Hardhat MetaMask Connector is a tool to connect your MetaMask wallet with your Hardhat development environment. Deploy and interact with smart contracts using your MetaMask wallet without exposing your mnemonic or private key in code.

Features

• Connect to MetaMask directly from Hardhat scripts
• Deploy contracts using your MetaMask wallet
• Sign transactions through MetaMask UI
• Support for multiple networks (localhost, Polygon, Ethereum, etc.)
• Automatic network switching
• No private keys in code - ever!

Install

npm install @web3camp/hardhat-metamask-connector

or

yarn add @web3camp/hardhat-metamask-connector

Quick Start

⚠️ Important: You must call await signer.getAddress() after getting the signer. This is what triggers the browser to open and establishes the MetaMask connection!

1. Import the connector

import { MetamaskConnector } from "@web3camp/hardhat-metamask-connector";

or

const { MetamaskConnector } = require("@web3camp/hardhat-metamask-connector");

2. Basic Usage

import { ethers } from "hardhat";
import { MetamaskConnector } from "@web3camp/hardhat-metamask-connector";

async function main() {
  // Initialize the connector
  const connector = new MetamaskConnector();

  // Get signer from MetaMask
  const signer = await connector.getSigner();

  // IMPORTANT: You MUST call getAddress() to trigger the browser to open
  // and wait for MetaMask connection. This is a required step!
  const signerAddr = await signer.getAddress();
  console.log("Signer Address:", signerAddr);

  // Now you can deploy contracts using MetaMask
  const MyContract = await ethers.getContractFactory("MyContract");
  const contract = await MyContract.connect(signer).deploy();
  await contract.waitForDeployment();

  console.log("Contract deployed to:", await contract.getAddress());

  // Close the connector when done
  connector.close();
}

main();

3. Run your script

# For localhost network
npx hardhat run scripts/deploy.ts --network localhost

# For Polygon network
npx hardhat run scripts/deploy.ts --network polygon

# For any configured network
npx hardhat run scripts/deploy.ts --network <network-name>

How It Works

1. Initialize connector: new MetamaskConnector() creates a local web server (default port 8989)
2. Get signer: await connector.getSigner() returns a signer object
3. Trigger browser: await signer.getAddress() opens the browser and waits for MetaMask connection
4. Connect MetaMask: Click "Connect to MetaMask" in the browser and approve the connection
5. Network switch: MetaMask automatically switches to the correct network
6. Sign transactions: Approve transactions in MetaMask as they come
7. Script continues: Your Hardhat script receives the signed transactions

Important: You must call await signer.getAddress() before using the signer. This triggers the browser to open and establishes the MetaMask connection. Without this call, the browser won't open!

Configuration

Custom Server Port

// Use a custom port (default is 8989)
const connector = new MetamaskConnector(9000);

Network Configuration

Configure networks in your hardhat.config.ts:

import { HardhatUserConfig } from "hardhat/config";

// You can use any dummy private key here - it won't be used
// This is just to satisfy Hardhat's requirement
const DUMMY_PRIVATE_KEY = "0xac0974bec39a17e36ba4a6b4d238ff944bacb478cbed5efcae784d7bf4f2ff80";

const config: HardhatUserConfig = {
  networks: {
    localhost: {
      url: "http://127.0.0.1:8545",
      chainId: 31337,
    },
    polygon: {
      url: "https://polygon-mainnet.infura.io/v3/YOUR_INFURA_KEY",
      chainId: 137,
      // IMPORTANT: Hardhat requires the accounts field even though we use MetaMask
      // You can use any dummy private key here - it will NOT be used
      accounts: [DUMMY_PRIVATE_KEY]
    },
    mainnet: {
      url: "https://eth.llamarpc.com",
      chainId: 1,
      accounts: [DUMMY_PRIVATE_KEY]
    }
  }
};

export default config;

⚠️ Important Hardhat Quirk: Even though MetaMask Connector doesn't use private keys, Hardhat still requires the accounts field in network configuration for non-localhost networks. You can use any dummy private key (like the default Hardhat test key shown above) - it will never be used. Your actual transactions will be signed by MetaMask!

Complete Example

See the example folder for a full working example:

cd example
npm install
npx hardhat node  # In one terminal
npx hardhat run scripts/deploy.ts --network localhost  # In another terminal

Browser Console Logs

When using the connector, you'll see helpful logs in the browser console (F12):

• Current MetaMask chainId: 0x89 - Shows the connected network
• Switched to chainId: 0x89 - Confirms network switch
• Transaction sent: 0x123... - Transaction hash
• Verify at: https://polygonscan.com/tx/0x123... - Block explorer link

Troubleshooting

Browser doesn't open automatically

• Make sure you called await signer.getAddress() - this is what triggers the browser to open
• If you still have issues, manually open the URL shown in the console (e.g., http://localhost:8989/send-tx)

Wrong network

• The connector will prompt MetaMask to switch to the correct network
• Make sure to approve the network switch in MetaMask

Transaction not appearing on block explorer

• Check the browser console for the chainId - ensure it matches your expected network
• Verify MetaMask is on the correct network

Error: "Cannot read properties of undefined"

• Make sure you have the accounts field in your network configuration in hardhat.config.ts
• Hardhat requires this field even though MetaMask Connector doesn't use it
• Use a dummy private key: accounts: ["0xac0974bec39a17e36ba4a6b4d238ff944bacb478cbed5efcae784d7bf4f2ff80"]

Port already in use

• Change the port: new MetamaskConnector(9000)
• Or kill the process using port 8989

Supported Networks

The connector automatically shows block explorer links for:

• Ethereum Mainnet (etherscan.io)
• Polygon (polygonscan.com)
• Optimism (optimistic.etherscan.io)
• Arbitrum (arbiscan.io)
• Base (basescan.org)
• Any Hardhat local network

The idea

To be continue

• [x] Inject signer to ethers
• [x] Optimize the launch of the browser
• [x] Optimize the webpage
• [ ] Add support of other wallets
  • [ ] Coinbase Wallet
  • [ ] OKX Wallet
  • [ ] WalletConnect

Special thanks

hardhat-metamask-client