Hardhat Setup Skill

This skill provides templates, scripts, and best practices for setting up Hardhat-based Solidity projects.

When to Use

Use this skill when:

• Initializing a new Hardhat project
• Adding Hardhat to an existing Solidity codebase
• Configuring Hardhat settings (networks, plugins, etc.)
• Setting up Hardhat in a hybrid Foundry/Hardhat project
• Updating Hardhat configuration

Prerequisites: Node.js and npm/yarn/pnpm must be installed

Integration with Framework Detection

Before using this skill, reference the

framework-detection

• Check if Hardhat is already configured
• Determine if this is a hybrid setup
• Avoid overwriting existing configuration

Quick Setup

Basic Initialization

# Initialize new Hardhat project
npm init -y
npm install --save-dev hardhat
npx hardhat init

# Or with yarn
yarn init -y
yarn add --dev hardhat
npx hardhat init

Project Structure

Hardhat creates this structure:

project/
├── hardhat.config.js     # Configuration
├── .env                  # Environment variables
├── package.json          # Dependencies
├── contracts/            # Contract source files
│   └── Lock.sol          # Example contract
├── test/                 # Test files
│   └── Lock.js           # Example test
├── scripts/              # Deployment scripts
│   └── deploy.js         # Example script
└── ignition/             # Hardhat Ignition (deployment modules)

Configuration Templates

hardhat.config.js

See

./templates/hardhat.config.js

Key Configuration Sections:

require("@nomicfoundation/hardhat-toolbox");
require("dotenv").config();

module.exports = {
  solidity: {
    version: "0.8.30",
    settings: {
      optimizer: {
        enabled: true,
        runs: 200
      }
    }
  },
  networks: {
    hardhat: {},
    sepolia: {
      url: process.env.SEPOLIA_RPC_URL || "",
      accounts: process.env.PRIVATE_KEY ? [process.env.PRIVATE_KEY] : []
    }
  },
  etherscan: {
    apiKey: process.env.ETHERSCAN_API_KEY
  }
};

hardhat.config.ts

See

./templates/hardhat.config.ts

TypeScript Configuration:

import { HardhatUserConfig } from "hardhat/config";
import "@nomicfoundation/hardhat-toolbox";
import "dotenv/config";

const config: HardhatUserConfig = {
  solidity: "0.8.30",
  networks: {
    sepolia: {
      url: process.env.SEPOLIA_RPC_URL || "",
      accounts: process.env.PRIVATE_KEY ? [process.env.PRIVATE_KEY] : []
    }
  }
};

export default config;

Environment Variables

See

./templates/.env.example

Essential Variables:

# RPC URLs
MAINNET_RPC_URL=
SEPOLIA_RPC_URL=

# Private Keys (NEVER commit actual keys)
PRIVATE_KEY=

# Etherscan API Keys
ETHERSCAN_API_KEY=

# Gas Settings
GAS_PRICE=

Essential Plugins

Hardhat Toolbox (Recommended)

Includes all essential plugins:

npm install --save-dev @nomicfoundation/hardhat-toolbox

Includes:

• @nomicfoundation/hardhat-ethers

  - Ethers.js integration

• @nomicfoundation/hardhat-chai-matchers

  - Chai matchers for testing

• @nomicfoundation/hardhat-verify

  - Contract verification

• hardhat-gas-reporter

  - Gas usage reporting

• solidity-coverage

  - Code coverage

• @typechain/hardhat

  - TypeScript types for contracts

Individual Plugins

# Contract verification
npm install --save-dev @nomicfoundation/hardhat-verify

# Gas reporting
npm install --save-dev hardhat-gas-reporter

# Code coverage
npm install --save-dev solidity-coverage

# OpenZeppelin Upgrades
npm install --save-dev @openzeppelin/hardhat-upgrades

Common Configurations

1. Multiple Networks

networks: {
  mainnet: {
    url: process.env.MAINNET_RPC_URL,
    accounts: [process.env.PRIVATE_KEY],
    chainId: 1
  },
  sepolia: {
    url: process.env.SEPOLIA_RPC_URL,
    accounts: [process.env.PRIVATE_KEY],
    chainId: 11155111
  },
  arbitrum: {
    url: process.env.ARBITRUM_RPC_URL,
    accounts: [process.env.PRIVATE_KEY],
    chainId: 42161
  }
}

2. High Optimization for Production

solidity: {
  version: "0.8.30",
  settings: {
    optimizer: {
      enabled: true,
      runs: 10000
    },
    viaIR: true
  }
}

3. Multiple Solidity Versions

solidity: {
  compilers: [
    {
      version: "0.8.30",
      settings: {
        optimizer: { enabled: true, runs: 200 }
      }
    },
    {
      version: "0.8.20",
      settings: {
        optimizer: { enabled: true, runs: 200 }
      }
    }
  ]
}

4. Gas Reporter Configuration

gasReporter: {
  enabled: process.env.REPORT_GAS === "true",
  currency: "USD",
  coinmarketcap: process.env.COINMARKETCAP_API_KEY,
  outputFile: "gas-report.txt",
  noColors: true
}

Dependencies Management

Installing OpenZeppelin

# OpenZeppelin Contracts
npm install @openzeppelin/contracts

# OpenZeppelin Upgrades Plugin
npm install --save-dev @openzeppelin/hardhat-upgrades

Installing Common Libraries

# Ethers.js (usually included with hardhat-toolbox)
npm install ethers

# Chai for testing
npm install --save-dev chai

# Dotenv for environment variables
npm install --save-dev dotenv

Initialization Script

See

./scripts/init-hardhat.sh

Usage:

# Basic initialization
./scripts/init-hardhat.sh

# With project name
./scripts/init-hardhat.sh my-project

# With TypeScript
./scripts/init-hardhat.sh my-project --typescript

What the script does:

1. Checks if Node.js is installed
2. Initializes npm/yarn project
3. Installs Hardhat and essential plugins
4. Creates configuration files
5. Sets up .gitignore
6. Installs OpenZeppelin contracts
7. Creates example contract and test

Hybrid Setup (Hardhat + Foundry)

When adding Hardhat to an existing Foundry project:

1. Initialize Hardhat Without Overwriting

# Initialize npm project
npm init -y

# Install Hardhat
npm install --save-dev hardhat
npx hardhat init  # Choose "Create an empty hardhat.config.js"

2. Configure Shared Directories

// hardhat.config.js
module.exports = {
  paths: {
    sources: "./src",      // Use Foundry's src dir
    tests: "./test",       // Shared test dir
    cache: "./cache_hardhat",  // Separate cache
    artifacts: "./artifacts"
  },
  solidity: "0.8.30"
};

3. Update .gitignore

# Hardhat
artifacts/
cache/
cache_hardhat/
node_modules/
coverage/
coverage.json
typechain-types/

# Foundry
out/
lib/

# Environment
.env
.env.local

4. Shared Dependencies

# Install OpenZeppelin via npm (for Hardhat)
npm install @openzeppelin/contracts

# Foundry can reference node_modules
# Add to foundry.toml:
# libs = ["node_modules", "lib"]

Testing Setup

Basic Test Structure (JavaScript)

const { expect } = require("chai");
const { ethers } = require("hardhat");

describe("MyContract", function () {
  let myContract;
  let owner;

  beforeEach(async function () {
    [owner] = await ethers.getSigners();
    const MyContract = await ethers.getContractFactory("MyContract");
    myContract = await MyContract.deploy();
  });

  it("Should work correctly", async function () {
    // Test implementation
    expect(await myContract.someFunction()).to.equal(expectedValue);
  });
});

Basic Test Structure (TypeScript)

import { expect } from "chai";
import { ethers } from "hardhat";
import { MyContract } from "../typechain-types";

describe("MyContract", function () {
  let myContract: MyContract;

  beforeEach(async function () {
    const MyContract = await ethers.getContractFactory("MyContract");
    myContract = await MyContract.deploy();
  });

  it("Should work correctly", async function () {
    expect(await myContract.someFunction()).to.equal(expectedValue);
  });
});

Running Tests

# Run all tests
npx hardhat test

# Run specific test
npx hardhat test test/MyContract.test.js

# With gas reporting
REPORT_GAS=true npx hardhat test

# With coverage
npx hardhat coverage

Security Best Practices for Private Keys

⚠️ CRITICAL: Never store production private keys in .env files!

Recommended Approaches (in order of preference)

1. Hardware Wallets (Most Secure - Production)

Install the Ledger plugin:

npm install --save-dev @nomicfoundation/hardhat-ledger

Configure in

hardhat.config.js

require("@nomicfoundation/hardhat-ledger");

module.exports = {
  networks: {
    mainnet: {
      url: process.env.MAINNET_RPC_URL,
      ledgerAccounts: [
        "0xYourLedgerAddress"
      ]
    }
  }
};

Deploy with Ledger:

npx hardhat run scripts/deploy.js --network mainnet

2. Hardhat Configuration Variables (Recommended - Built-in)

Hardhat 2.x+ includes built-in support for secure configuration variables:

# Set a configuration variable (prompts for value, stores encrypted)
npx hardhat vars set PRIVATE_KEY

# List all configuration variables
npx hardhat vars list

# Delete a variable
npx hardhat vars delete PRIVATE_KEY

Use in

hardhat.config.js

const { vars } = require("hardhat/config");

module.exports = {
  networks: {
    sepolia: {
      url: vars.get("SEPOLIA_RPC_URL"),
      accounts: [vars.get("PRIVATE_KEY")]
    }
  }
};

This stores encrypted values in your home directory and prompts for decryption when needed.

3. hardhat-keystore Plugin (Encrypted Keystore)

Similar to Foundry's

cast wallet

npm install --save-dev hardhat-keystore

Configure in

hardhat.config.js

require("hardhat-keystore");

module.exports = {
  networks: {
    sepolia: {
      url: process.env.SEPOLIA_RPC_URL,
      accounts: {
        mnemonic: keystore.getMnemonic(),
        // or
        privateKey: keystore.getPrivateKey("deployer")
      }
    }
  }
};

4. hardhat-secure-accounts Plugin (Third-Party Alternative)

npm install --save-dev hardhat-secure-accounts

Creates encrypted keystore files:

# Create new encrypted account
npx hardhat accounts:create

# Import existing private key
npx hardhat accounts:import --name deployer

Use in scripts:

const { getSecureAccount } = require("hardhat-secure-accounts");

async function main() {
  const signer = await getSecureAccount("deployer");
  // Use signer for deployment
}

5. Interactive Environment Variable (Development Only)

Prompt for private key at runtime (doesn't store on disk):

const readline = require("readline");

async function getPrivateKey() {
  const rl = readline.createInterface({
    input: process.stdin,
    output: process.stdout
  });

  return new Promise((resolve) => {
    rl.question("Enter private key: ", (answer) => {
      rl.close();
      resolve(answer);
    });
  });
}

async function main() {
  const privateKey = await getPrivateKey();
  const wallet = new ethers.Wallet(privateKey, ethers.provider);
  // Use wallet for deployment
}

6. .env Variables (Development/Testing ONLY)

⚠️ Use ONLY for local development or testnet testing with non-production keys!

require("dotenv").config();

module.exports = {
  networks: {
    sepolia: {
      url: process.env.SEPOLIA_RPC_URL,
      accounts: process.env.PRIVATE_KEY ? [process.env.PRIVATE_KEY] : []
    }
  }
};

If using .env:

• ✅ Only use accounts created specifically for development/testing
• ✅ Never reuse production private keys
• ✅ Keep test funds minimal
• ✅ Add .env to .gitignore
• ❌ Never commit .env to version control
• ❌ Never use for mainnet deployments

Deployment Setup

Basic Deployment Script

// scripts/deploy.js
const hre = require("hardhat");

async function main() {
  const MyContract = await hre.ethers.getContractFactory("MyContract");
  const myContract = await MyContract.deploy();
  await myContract.waitForDeployment();

  console.log("MyContract deployed to:", await myContract.getAddress());
}

main()
  .then(() => process.exit(0))
  .catch((error) => {
    console.error(error);
    process.exit(1);
  });

Deploy Commands

# Deploy to local network
npx hardhat run scripts/deploy.js

# Deploy to Sepolia with hardware wallet (RECOMMENDED for production)
npx hardhat run scripts/deploy.js --network sepolia
# (Ledger will prompt for approval)

# Deploy to Sepolia with Hardhat vars (RECOMMENDED for all deployments)
# First time: npx hardhat vars set PRIVATE_KEY
npx hardhat run scripts/deploy.js --network sepolia

# Development only: with .env private key
npx hardhat run scripts/deploy.js --network sepolia

# Verify contract
npx hardhat verify --network sepolia DEPLOYED_CONTRACT_ADDRESS

Best Practices

1. Secure private key management - Use hardware wallets or Hardhat Configuration Variables for all deployments; never store production keys in .env
2. Use hardhat-toolbox - Includes all essential plugins
3. TypeScript for large projects - Better type safety and IDE support
4. Comprehensive .env.example - Document all required environment variables (but discourage private keys)
5. Separate networks - Configure all networks you'll deploy to
6. Gas reporting - Enable gas reports for optimization
7. Code coverage - Run coverage regularly
8. Contract verification - Always verify deployed contracts
9. Version lock dependencies - Use exact versions in package.json

Troubleshooting

Issue: "hardhat: command not found"

# Use npx
npx hardhat compile

# Or install globally (not recommended)
npm install -g hardhat

Issue: Module not found errors

# Clear cache and reinstall
rm -rf node_modules package-lock.json
npm install

Issue: Compilation errors with OpenZeppelin

# Ensure correct import paths
import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

Issue: Network connection errors

# Check RPC URL in .env
# Test with curl
curl -X POST -H "Content-Type: application/json" \
  --data '{"jsonrpc":"2.0","method":"eth_blockNumber","params":[],"id":1}' \
  $SEPOLIA_RPC_URL

Quick Reference

npx hardhat init

npm install <package>

npx hardhat compile

npx hardhat test

npx hardhat coverage

REPORT_GAS=true npx hardhat test

npx hardhat run scripts/deploy.js

npx hardhat verify

npx hardhat clean

Template Files

This skill provides the following templates:

• ./templates/hardhat.config.js

  - JavaScript configuration

• ./templates/hardhat.config.ts

  - TypeScript configuration

• ./templates/.env.example

  - Environment variables template

• ./templates/deploy-script.js

  - Deployment script template

Scripts

This skill provides the following scripts:

• ./scripts/init-hardhat.sh

  - Automated project initialization

Next Steps After Setup:

1. Configure

   hardhat.config.js

   for your networks
2. Copy

   .env.example

   to

   .env

   and fill in values
3. Install required dependencies with

   npm install

4. Write contracts in

   contracts/

5. Write tests in

   test/

6. Run

   npx hardhat test

   to verify setup