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Hardhat

By · Reviewed & last updated · Part of Web3 & Solidity Tutorial

Hardhat is the Node.js development environment for Ethereum: local network, console, testing framework, and deployment tooling in one CLI. The workflow is write contract → write test → run the test against an in-memory Hardhat Network → deploy to a real chain. This example covers the full loop for a tiny token contract.

Test and deploy an ERC-20-lite token

EXAMPLE
// contracts/Token.sol
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

contract Token {
    string public name = 'DemoToken';
    string public symbol = 'DEMO';
    uint8  public decimals = 18;
    uint256 public totalSupply;
    mapping(address => uint256) public balanceOf;
    event Transfer(address indexed from, address indexed to, uint256 value);

    constructor(uint256 initialSupply) {
        totalSupply = initialSupply;
        balanceOf[msg.sender] = initialSupply;
        emit Transfer(address(0), msg.sender, initialSupply);
    }

    function transfer(address to, uint256 amount) external returns (bool) {
        require(balanceOf[msg.sender] >= amount, 'insufficient');
        unchecked { balanceOf[msg.sender] -= amount; }
        balanceOf[to] += amount;
        emit Transfer(msg.sender, to, amount);
        return true;
    }
}

// test/Token.ts
import { expect } from 'chai';
import { ethers } from 'hardhat';

describe('Token', () => {
  it('mints supply to deployer and transfers', async () => {
    const [deployer, alice] = await ethers.getSigners();
    const Token = await ethers.getContractFactory('Token');
    const supply = ethers.parseEther('1000');
    const token = await Token.deploy(supply);

    expect(await token.balanceOf(deployer.address)).to.equal(supply);

    await expect(token.transfer(alice.address, ethers.parseEther('10')))
      .to.emit(token, 'Transfer')
      .withArgs(deployer.address, alice.address, ethers.parseEther('10'));

    expect(await token.balanceOf(alice.address))
      .to.equal(ethers.parseEther('10'));
  });
});

// scripts/deploy.ts
import { ethers } from 'hardhat';

async function main() {
  const supply = ethers.parseEther('1000000');
  const token = await ethers.deployContract('Token', [supply]);
  await token.waitForDeployment();
  console.log('Token deployed to', await token.getAddress());
}
main().catch((e) => { console.error(e); process.exit(1); });

// Run: npx hardhat test
// Local deploy: npx hardhat node  (separate terminal)
//               npx hardhat run scripts/deploy.ts --network localhost

Why it matters

Hardhat Network forks mainnet on demand — `npx hardhat node --fork ` gives you a local chain that pretends to be mainnet at the current block. That is how you test against real Uniswap, real USDC, real anything, without paying gas or risking funds.

Tip: Tweak the snippet with Try it Yourself », then sit the quiz at the bottom of the page.

Example

Example
// hardhat.config.ts
import "@nomicfoundation/hardhat-toolbox";
export default {
    solidity: "0.8.24",
    networks: {
        sepolia: {
            url: process.env.SEPOLIA_RPC,
            accounts: [process.env.PRIVATE_KEY!],
        },
    },
};
// npx hardhat test
// npx hardhat run scripts/deploy.ts --network sepolia
Try it Yourself »

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