Hardhat Framework Skill

Expert-level usage of Hardhat, the most popular Ethereum development environment.

Capabilities

• Configuration: Set up hardhat.config.js for multi-network
• Testing: Write tests with ethers.js/viem
• Plugins: Use plugins (upgrades, gas-reporter, coverage)
• Local Network: Run Hardhat Network for development
• Deployment: Execute scripts and manage deployments
• Forking: Fork mainnet for testing
• TypeChain: Generate TypeScript typings

Installation

# Create project
mkdir my-project && cd my-project
npm init -y

# Install Hardhat
npm install --save-dev hardhat

# Initialize project
npx hardhat init

# Install common dependencies
npm install --save-dev @nomicfoundation/hardhat-toolbox

Configuration

hardhat.config.js

require("@nomicfoundation/hardhat-toolbox");
require("@openzeppelin/hardhat-upgrades");
require("hardhat-gas-reporter");
require("solidity-coverage");

/** @type import('hardhat/config').HardhatUserConfig */
module.exports = {
  solidity: {
    version: "0.8.20",
    settings: {
      optimizer: {
        enabled: true,
        runs: 200,
      },
      viaIR: false,
    },
  },

  networks: {
    hardhat: {
      forking: {
        url: process.env.MAINNET_RPC_URL,
        blockNumber: 18000000,
      },
    },
    sepolia: {
      url: process.env.SEPOLIA_RPC_URL,
      accounts: [process.env.PRIVATE_KEY],
    },
    mainnet: {
      url: process.env.MAINNET_RPC_URL,
      accounts: [process.env.PRIVATE_KEY],
    },
  },

  etherscan: {
    apiKey: process.env.ETHERSCAN_API_KEY,
  },

  gasReporter: {
    enabled: true,
    currency: "USD",
    coinmarketcap: process.env.COINMARKETCAP_API_KEY,
  },

  paths: {
    sources: "./contracts",
    tests: "./test",
    cache: "./cache",
    artifacts: "./artifacts",
  },
};

TypeScript Configuration

// hardhat.config.ts
import { HardhatUserConfig } from "hardhat/config";
import "@nomicfoundation/hardhat-toolbox";
import "@openzeppelin/hardhat-upgrades";

const config: HardhatUserConfig = {
  solidity: "0.8.20",
  networks: {
    sepolia: {
      url: process.env.SEPOLIA_RPC_URL || "",
      accounts: process.env.PRIVATE_KEY ? [process.env.PRIVATE_KEY] : [],
    },
  },
};

export default config;

Testing

Basic Test

// test/Token.test.js
const { expect } = require("chai");
const { ethers } = require("hardhat");

describe("Token", function () {
  let token;
  let owner;
  let addr1;

  beforeEach(async function () {
    [owner, addr1] = await ethers.getSigners();

    const Token = await ethers.getContractFactory("Token");
    token = await Token.deploy();
    await token.waitForDeployment();
  });

  describe("Deployment", function () {
    it("Should set the right owner", async function () {
      expect(await token.owner()).to.equal(owner.address);
    });

    it("Should assign total supply to owner", async function () {
      const ownerBalance = await token.balanceOf(owner.address);
      expect(await token.totalSupply()).to.equal(ownerBalance);
    });
  });

  describe("Transactions", function () {
    it("Should transfer tokens", async function () {
      await token.transfer(addr1.address, 50);
      expect(await token.balanceOf(addr1.address)).to.equal(50);
    });

    it("Should emit Transfer event", async function () {
      await expect(token.transfer(addr1.address, 50))
        .to.emit(token, "Transfer")
        .withArgs(owner.address, addr1.address, 50);
    });

    it("Should fail if sender lacks funds", async function () {
      await expect(
        token.connect(addr1).transfer(owner.address, 1)
      ).to.be.revertedWith("Insufficient balance");
    });
  });
});

TypeScript Test

// test/Token.test.ts
import { expect } from "chai";
import { ethers } from "hardhat";
import { Token } from "../typechain-types";

describe("Token", function () {
  let token: Token;

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

  it("Should deploy successfully", async function () {
    expect(await token.getAddress()).to.be.properAddress;
  });
});

Fork Testing

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

describe("Fork Test", function () {
  const USDC_ADDRESS = "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48";
  const WHALE = "0x47ac0Fb4F2D84898e4D9E7b4DaB3C24507a6D503";

  beforeEach(async function () {
    // Impersonate whale account
    await network.provider.request({
      method: "hardhat_impersonateAccount",
      params: [WHALE],
    });
  });

  it("Should transfer USDC from whale", async function () {
    const whale = await ethers.getSigner(WHALE);
    const usdc = await ethers.getContractAt("IERC20", USDC_ADDRESS);

    const [, recipient] = await ethers.getSigners();
    const amount = ethers.parseUnits("1000", 6);

    await usdc.connect(whale).transfer(recipient.address, amount);
    expect(await usdc.balanceOf(recipient.address)).to.equal(amount);
  });
});

Deployment Scripts

Basic Deployment

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

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

  console.log("Token deployed to:", await token.getAddress());

  // Verify on Etherscan
  if (hre.network.name !== "hardhat") {
    await hre.run("verify:verify", {
      address: await token.getAddress(),
      constructorArguments: [],
    });
  }
}

main().catch((error) => {
  console.error(error);
  process.exitCode = 1;
});

Upgradeable Deployment

// scripts/deploy-upgradeable.js
const { ethers, upgrades } = require("hardhat");

async function main() {
  const Token = await ethers.getContractFactory("TokenV1");

  // Deploy proxy
  const token = await upgrades.deployProxy(Token, [], {
    initializer: "initialize",
  });
  await token.waitForDeployment();

  console.log("Proxy deployed to:", await token.getAddress());
}

main();

Upgrade Script

// scripts/upgrade.js
const { ethers, upgrades } = require("hardhat");

async function main() {
  const PROXY_ADDRESS = "0x...";

  const TokenV2 = await ethers.getContractFactory("TokenV2");
  const token = await upgrades.upgradeProxy(PROXY_ADDRESS, TokenV2);

  console.log("Token upgraded");
}

main();

Hardhat Tasks

// hardhat.config.js
task("accounts", "Prints accounts", async (taskArgs, hre) => {
  const accounts = await hre.ethers.getSigners();
  for (const account of accounts) {
    console.log(account.address);
  }
});

task("balance", "Prints balance")
  .addParam("account", "The account address")
  .setAction(async (taskArgs, hre) => {
    const balance = await hre.ethers.provider.getBalance(taskArgs.account);
    console.log(hre.ethers.formatEther(balance), "ETH");
  });

Commands

# Compile
npx hardhat compile

# Test
npx hardhat test
npx hardhat test --grep "transfer"

# Coverage
npx hardhat coverage

# Run script
npx hardhat run scripts/deploy.js --network sepolia

# Console
npx hardhat console --network localhost

# Node
npx hardhat node

# Verify
npx hardhat verify --network mainnet <address>

Process Integration

Best Practices

1. Use TypeScript for type safety
2. Configure multiple networks
3. Use environment variables
4. Enable gas reporting
5. Generate coverage reports
6. Verify contracts on explorers

See Also

• skills/foundry-framework/SKILL.md - Alternative framework
• skills/openzeppelin/SKILL.md - Contract libraries
• Hardhat Documentation