Deploy your first smart contract on Sepolia with Hardhat

Hardhat is the most widely used Solidity development environment. It runs on Node.js, integrates with the entire JavaScript ecosystem, and has a rich plugin library. If your team is already JavaScript-heavy, Hardhat is the natural choice.

Prerequisites

• Node.js 20+ installed
• A Sepolia RPC URL (use https://ethereum-sepolia-rpc.publicnode.com for free)
• Sepolia ETH from a faucet — see the faucets page
• Basic Solidity and JavaScript knowledge

1. Create a new project

mkdir my-hardhat-project && cd my-hardhat-project
npm init -y
npm install --save-dev hardhat @nomicfoundation/hardhat-toolbox
npx hardhat init

Choose “Create a JavaScript project” when prompted and accept the defaults.

2. Write your contract

Replace contracts/Lock.sol with a simple counter:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

contract Counter {
    uint256 public count;

    event Incremented(address indexed by, uint256 newCount);

    function increment() external {
        count += 1;
        emit Incremented(msg.sender, count);
    }

    function reset() external {
        count = 0;
    }
}

3. Write a test

Replace test/Lock.js with:

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

describe("Counter", function () {
  async function deploy() {
    const Counter = await ethers.getContractFactory("Counter");
    const counter = await Counter.deploy();
    return { counter };
  }

  it("starts at zero", async function () {
    const { counter } = await deploy();
    expect(await counter.count()).to.equal(0n);
  });

  it("increments", async function () {
    const { counter } = await deploy();
    await counter.increment();
    expect(await counter.count()).to.equal(1n);
  });

  it("resets", async function () {
    const { counter } = await deploy();
    await counter.increment();
    await counter.reset();
    expect(await counter.count()).to.equal(0n);
  });
});

Run the tests locally:

npx hardhat test

4. Configure Sepolia

Open hardhat.config.js and replace its contents:

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

const PRIVATE_KEY = process.env.PRIVATE_KEY;
const SEPOLIA_RPC = process.env.SEPOLIA_RPC || "https://ethereum-sepolia-rpc.publicnode.com";

module.exports = {
  solidity: "0.8.24",
  networks: {
    sepolia: {
      url: SEPOLIA_RPC,
      accounts: PRIVATE_KEY ? [PRIVATE_KEY] : [],
    },
  },
};

Create a .env file (and add it to .gitignore):

PRIVATE_KEY=0xYOUR_PRIVATE_KEY_HERE

Install dotenv support:

npm install dotenv

Add require("dotenv").config(); at the top of hardhat.config.js.

5. Write a deploy script

Create scripts/deploy.js:

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

async function main() {
  const [deployer] = await ethers.getSigners();
  console.log("Deploying from:", deployer.address);

  const Counter = await ethers.getContractFactory("Counter");
  const counter = await Counter.deploy();
  await counter.waitForDeployment();

  console.log("Counter deployed to:", await counter.getAddress());
}

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

6. Deploy to Sepolia

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

You will see something like:

Deploying from: 0xYourAddress
Counter deployed to: 0xDeployedContractAddress

Verify on Sepolia Etherscan by searching for the deployed address.

7. Interact with the contract

Use the Hardhat console to call your contract:

npx hardhat console --network sepolia

const Counter = await ethers.getContractFactory("Counter");
const counter = Counter.attach("0xDeployedContractAddress");

await counter.count();         // 0n
await counter.increment();
await counter.count();         // 1n

Useful commands

Next steps

• Add Hardhat Ignition for reproducible deployments
• Verify your contract on Etherscan with @nomicfoundation/hardhat-verify
• Explore the same contract on Base Sepolia using the OP Stack