Hardhat

Hardhat

Hardhat is the dominant Solidity development framework. It provides compilation, testing, deployment, and debugging for EVM smart contracts. The core value is Hardhat Network — a local EVM that supports console.log, stack traces, and mainnet forking. All configuration lives in hardhat.config.ts.

What You Probably Got Wrong

LLMs frequently generate Hardhat code mixing v1 patterns, ethers v5 syntax, and deprecated plugins. These corrections are non-negotiable.

• ethers v6, not v5 — the API changed fundamentally — Hardhat toolbox now bundles ethers v6. ethers.getContractFactory() returns a different type. parseEther() is a standalone import, not ethers.utils.parseEther(). BigNumber is gone — ethers v6 uses native bigint. If you see BigNumber.from() or ethers.utils.*, you are writing v5 code. Stop.
• hardhat-deploy is NOT the official deployment tool — The official deployment system is Hardhat Ignition (@nomicfoundation/hardhat-ignition). hardhat-deploy by wighawag is a community plugin that is not maintained by the Hardhat team. Use Ignition for new projects.
• @nomicfoundation/hardhat-toolbox replaces individual plugins — Do not install @nomiclabs/hardhat-ethers, @nomiclabs/hardhat-waffle, or hardhat-gas-reporter individually. The hardhat-toolbox meta-plugin includes ethers, chai matchers, coverage, gas reporter, and typechain. The old @nomiclabs/ scoped packages are deprecated.
• npx hardhat compile does NOT generate TypeScript types by default — You must have @nomicfoundation/hardhat-toolbox (or @typechain/hardhat) installed AND run npx hardhat compile to generate types in typechain-types/. The types are not checked into source control.
• hardhat.config.ts is NOT optional for TypeScript — If you use .ts config, you must have ts-node and typescript installed. Hardhat uses ts-node to transpile the config at runtime. Without it, Hardhat silently falls back to looking for .js.
• ethers.getSigners() returns HardhatEthersSigner, not raw ethers Signer — The signer type is HardhatEthersSigner which extends ethers AbstractSigner. It has additional properties like .address as a direct property (not a method). Type your test variables accordingly.
• Hardhat Network resets between test files, not between it() blocks — State persists across it() blocks within the same describe(). Use loadFixture() from @nomicfoundation/hardhat-toolbox/network-helpers to get clean state per test. Do not rely on beforeEach deploying fresh contracts — it is slower and error-prone.
• Forking requires an archive node RPC — hardhat_reset and forking.blockNumber require archive data. Standard RPC endpoints only serve recent state. Use Alchemy or Infura archive tier, or a local archive node.
• console.log in Solidity only works on Hardhat Network — import "hardhat/console.sol" is a Hardhat-specific feature. It does nothing on mainnet, testnets, or other local nodes. Do not leave console.log in production contracts — it wastes gas on the import.
• Constructor arguments for verification must match exactly — npx hardhat verify fails silently when constructor args do not match the deployed bytecode. Use the --constructor-args flag pointing to a JS file that exports the exact arguments used during deployment.

Quick Start

New Project

mkdir my-project && cd my-project
npx hardhat init

Select "Create a TypeScript project". This generates:

my-project/
  contracts/          # Solidity source files
  ignition/modules/   # Hardhat Ignition deployment modules
  test/               # Mocha test files
  hardhat.config.ts   # Central configuration
  package.json
  tsconfig.json

Install Dependencies

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

hardhat-toolbox includes:

• @nomicfoundation/hardhat-ethers — ethers.js integration
• @nomicfoundation/hardhat-chai-matchers — Chai matchers for reverts, events, balance changes
• @nomicfoundation/hardhat-network-helpers — loadFixture, time, mine
• @typechain/hardhat — TypeScript type generation
• hardhat-gas-reporter — gas usage per function
• solidity-coverage — code coverage

Minimal Config

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

const config: HardhatUserConfig = {
  solidity: "0.8.27",
};

export default config;

First Compile + Test

npx hardhat compile
npx hardhat test

Configuration

Multi-Network Setup

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

const config: HardhatUserConfig = {
  solidity: {
    version: "0.8.27",
    settings: {
      optimizer: {
        enabled: true,
        runs: 200,
      },
      viaIR: false,
    },
  },
  networks: {
    hardhat: {
      chainId: 31337,
    },
    sepolia: {
      url: process.env.SEPOLIA_RPC_URL ?? "",
      accounts: process.env.DEPLOYER_PRIVATE_KEY
        ? [process.env.DEPLOYER_PRIVATE_KEY]
        : [],
    },
    mainnet: {
      url: process.env.MAINNET_RPC_URL ?? "",
      accounts: process.env.DEPLOYER_PRIVATE_KEY
        ? [process.env.DEPLOYER_PRIVATE_KEY]
        : [],
    },
    arbitrum: {
      url: process.env.ARBITRUM_RPC_URL ?? "",
      accounts: process.env.DEPLOYER_PRIVATE_KEY
        ? [process.env.DEPLOYER_PRIVATE_KEY]
        : [],
      chainId: 42161,
    },
    base: {
      url: process.env.BASE_RPC_URL ?? "",
      accounts: process.env.DEPLOYER_PRIVATE_KEY
        ? [process.env.DEPLOYER_PRIVATE_KEY]
        : [],
      chainId: 8453,
    },
  },
  etherscan: {
    apiKey: {
      mainnet: process.env.ETHERSCAN_API_KEY ?? "",
      sepolia: process.env.ETHERSCAN_API_KEY ?? "",
      arbitrumOne: process.env.ARBISCAN_API_KEY ?? "",
      base: process.env.BASESCAN_API_KEY ?? "",
    },
  },
  gasReporter: {
    enabled: process.env.REPORT_GAS === "true",
    currency: "USD",
    coinmarketcap: process.env.COINMARKETCAP_API_KEY,
  },
};

export default config;

Compiler Settings

solidity: {
  compilers: [
    {
      version: "0.8.27",
      settings: {
        optimizer: { enabled: true, runs: 200 },
        evmVersion: "cancun",
      },
    },
    {
      version: "0.8.20",
      settings: {
        optimizer: { enabled: true, runs: 1000 },
      },
    },
  ],
  overrides: {
    "contracts/Legacy.sol": {
      version: "0.8.17",
    },
  },
},

Multiple compiler versions let you compile contracts with different Solidity requirements in the same project.

Forking Configuration

networks: {
  hardhat: {
    forking: {
      url: process.env.MAINNET_RPC_URL ?? "",
      blockNumber: 19_000_000,
      enabled: true,
    },
  },
},

Pin blockNumber for deterministic tests. Without it, tests depend on live chain state and break when state changes.

Testing

Test Structure with Fixtures

import { expect } from "chai";
import { ethers } from "hardhat";
import { loadFixture } from "@nomicfoundation/hardhat-toolbox/network-helpers";

describe("Token", function () {
  async function deployTokenFixture() {
    const [owner, alice, bob] = await ethers.getSigners();
    const initialSupply = ethers.parseEther("1000000");

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

    return { token, owner, alice, bob, initialSupply };
  }

  describe("Deployment", function () {
    it("should set the correct total supply", async function () {
      const { token, initialSupply } = await loadFixture(deployTokenFixture);
      expect(await token.totalSupply()).to.equal(initialSupply);
    });

    it("should assign total supply to owner", async function () {
      const { token, owner, initialSupply } = await loadFixture(deployTokenFixture);
      expect(await token.balanceOf(owner.address)).to.equal(initialSupply);
    });
  });

  describe("Transfers", function () {
    it("should transfer tokens between accounts", async function () {
      const { token, owner, alice } = await loadFixture(deployTokenFixture);
      const amount = ethers.parseEther("100");

      await expect(token.transfer(alice.address, amount))
        .to.changeTokenBalances(token, [owner, alice], [-amount, amount]);
    });

    it("should revert on insufficient balance", async function () {
      const { token, alice, bob } = await loadFixture(deployTokenFixture);
      const amount = ethers.parseEther("1");

      await expect(token.connect(alice).transfer(bob.address, amount))
        .to.be.revertedWithCustomError(token, "ERC20InsufficientBalance");
    });
  });
});

Key Testing Patterns

Event Assertions

await expect(token.transfer(alice.address, amount))
  .to.emit(token, "Transfer")
  .withArgs(owner.address, alice.address, amount);

Custom Error Assertions

await expect(vault.withdraw(amount))
  .to.be.revertedWithCustomError(vault, "InsufficientBalance")
  .withArgs(currentBalance, amount);

Ether Balance Changes

await expect(payable.withdraw())
  .to.changeEtherBalances([payable, owner], [-amount, amount]);

Time Manipulation

import { time } from "@nomicfoundation/hardhat-toolbox/network-helpers";

await time.increase(3600);
await time.increaseTo(targetTimestamp);
await time.latestBlock();
const latest = await time.latest();

Impersonating Accounts

import { impersonateAccount, setBalance } from "@nomicfoundation/hardhat-toolbox/network-helpers";

const whaleAddress = "0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045";
await impersonateAccount(whaleAddress);
await setBalance(whaleAddress, ethers.parseEther("100"));

const whale = await ethers.getSigner(whaleAddress);
await token.connect(whale).transfer(recipient, amount);

Mining Control

import { mine, mineUpTo } from "@nomicfoundation/hardhat-toolbox/network-helpers";

await mine(10);
await mineUpTo(20_000_000);

Gas Reporter

Enable gas reporting in tests:

REPORT_GAS=true npx hardhat test

Output shows gas per function call and deployment cost.

Coverage

npx hardhat coverage

Generates coverage/ directory with HTML report. Coverage runs on a modified EVM — some tests may behave differently under coverage (gas-dependent assertions will fail).

Deployment with Hardhat Ignition

Hardhat Ignition is the declarative deployment system. Define what to deploy, Ignition handles execution order, retries, and state tracking.

Basic Module

// ignition/modules/Token.ts
import { buildModule } from "@nomicfoundation/hardhat-ignition/modules";
import { parseEther } from "ethers";

const TokenModule = buildModule("TokenModule", (m) => {
  const initialSupply = m.getParameter("initialSupply", parseEther("1000000"));

  const token = m.contract("Token", [initialSupply]);

  return { token };
});

export default TokenModule;

Deploy Command

npx hardhat ignition deploy ignition/modules/Token.ts --network sepolia

Module with Dependencies

// ignition/modules/Protocol.ts
import { buildModule } from "@nomicfoundation/hardhat-ignition/modules";

const ProtocolModule = buildModule("ProtocolModule", (m) => {
  const registry = m.contract("Registry");

  const vault = m.contract("Vault", [registry]);

  m.call(registry, "setVault", [vault]);

  const controller = m.contract("Controller", [registry, vault]);

  m.call(registry, "setController", [controller]);

  return { registry, vault, controller };
});

export default ProtocolModule;

Ignition resolves the dependency graph automatically. vault deploys after registry because it takes registry as a constructor arg. m.call() executes after the contract it references is deployed.

Parameters

const owner = m.getParameter("owner");
const fee = m.getParameter("fee", 300n);

Pass parameters via JSON file or CLI:

npx hardhat ignition deploy ignition/modules/Token.ts \
  --network sepolia \
  --parameters ignition/parameters.json

{
  "TokenModule": {
    "initialSupply": "1000000000000000000000000"
  }
}

Deployment State

Ignition stores deployment state in ignition/deployments/<deployment-id>/. This directory tracks which contracts deployed, their addresses, and which calls executed. Do not delete it — Ignition uses it for resumption and verification.

Verify After Deploy

npx hardhat ignition verify <deployment-id>

This reads constructor args from the deployment state. No need to specify them manually.

Contract Verification

Automatic (After Ignition Deploy)

npx hardhat ignition verify sepolia-deployment

Manual

npx hardhat verify --network sepolia \
  0xYOUR_CONTRACT_ADDRESS \
  "constructor_arg_1" \
  "constructor_arg_2"

Complex Constructor Args

Create a file for arguments:

// arguments.ts
export default [
  "0xTokenAddress",
  1000n,
  "My Token",
];

npx hardhat verify --network sepolia \
  --constructor-args arguments.ts \
  0xYOUR_CONTRACT_ADDRESS

Multi-Chain Verification

The etherscan.apiKey config accepts a map:

etherscan: {
  apiKey: {
    mainnet: process.env.ETHERSCAN_API_KEY ?? "",
    arbitrumOne: process.env.ARBISCAN_API_KEY ?? "",
    optimisticEthereum: process.env.OPTIMISTIC_ETHERSCAN_API_KEY ?? "",
    base: process.env.BASESCAN_API_KEY ?? "",
    polygon: process.env.POLYGONSCAN_API_KEY ?? "",
  },
},

Custom Chain Verification

For chains not natively supported by hardhat-verify:

etherscan: {
  apiKey: {
    monad: process.env.MONAD_EXPLORER_API_KEY ?? "",
  },
  customChains: [
    {
      network: "monad",
      chainId: 10143,
      urls: {
        apiURL: "https://explorer.monad.xyz/api",
        browserURL: "https://explorer.monad.xyz",
      },
    },
  ],
},

Hardhat Network

Console.log in Solidity

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.27;

import "hardhat/console.sol";

contract Vault {
    mapping(address => uint256) public balances;

    function deposit() external payable {
        console.log("Deposit from %s: %s wei", msg.sender, msg.value);
        balances[msg.sender] += msg.value;
    }
}

Remove console.log before deploying to production. It compiles to no-ops on non-Hardhat networks but the import still costs deployment gas.

Stack Traces

Hardhat Network provides Solidity stack traces on reverts. No configuration needed — revert reasons and the exact line number appear in test output automatically.

JSON-RPC Methods

Hardhat Network exposes additional JSON-RPC methods:

// Snapshot and revert (alternative to fixtures for special cases)
const snapshotId = await ethers.provider.send("evm_snapshot", []);
await ethers.provider.send("evm_revert", [snapshotId]);

// Set block timestamp
await ethers.provider.send("evm_setNextBlockTimestamp", [1700000000]);
await ethers.provider.send("evm_mine", []);

// Set account balance
await ethers.provider.send("hardhat_setBalance", [
  "0xAddress",
  "0xDE0B6B3A7640000", // 1 ETH in hex
]);

// Set storage slot directly
await ethers.provider.send("hardhat_setStorageAt", [
  contractAddress,
  "0x0", // slot 0
  "0x0000000000000000000000000000000000000000000000000000000000000001",
]);

// Reset fork
await ethers.provider.send("hardhat_reset", [
  {
    forking: {
      jsonRpcUrl: process.env.MAINNET_RPC_URL,
      blockNumber: 19_000_000,
    },
  },
]);

Mainnet Forking

Fork mainnet to test against real protocol state:

// hardhat.config.ts
networks: {
  hardhat: {
    forking: {
      url: process.env.MAINNET_RPC_URL ?? "",
      blockNumber: 19_500_000,
    },
  },
},

// test/ForkTest.ts
import { ethers } from "hardhat";

const USDC = "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48";
const WHALE = "0x47ac0Fb4F2D84898e4D9E7b4DaB3C24507a6D503"; // Binance hot wallet

describe("Fork Tests", function () {
  it("should read USDC balance on fork", async function () {
    const usdc = await ethers.getContractAt("IERC20", USDC);
    const balance = await usdc.balanceOf(WHALE);
    expect(balance).to.be.greaterThan(0n);
  });
});

Custom Tasks

Basic Task

// hardhat.config.ts (or tasks/accounts.ts if you split tasks into files)
import { task } from "hardhat/config";

task("accounts", "Prints the list of accounts", async (_taskArgs, hre) => {
  const accounts = await hre.ethers.getSigners();
  for (const account of accounts) {
    console.log(account.address);
  }
});

npx hardhat accounts

Task with Arguments

import { task } from "hardhat/config";

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

npx hardhat balance --account 0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266

Task Calling Other Tasks

task("deploy-and-verify", "Deploys and verifies a contract")
  .addParam("name", "Contract name")
  .setAction(async (taskArgs, hre) => {
    await hre.run("compile");

    const Contract = await hre.ethers.getContractFactory(taskArgs.name);
    const contract = await Contract.deploy();
    await contract.waitForDeployment();

    const address = await contract.getAddress();
    console.log(`${taskArgs.name} deployed to: ${address}`);

    if (hre.network.name !== "hardhat" && hre.network.name !== "localhost") {
      console.log("Waiting for block confirmations...");
      await contract.deploymentTransaction()?.wait(5);

      await hre.run("verify:verify", {
        address,
        constructorArguments: [],
      });
    }
  });

TypeScript Configuration

tsconfig.json

{
  "compilerOptions": {
    "target": "ES2020",
    "module": "commonjs",
    "esModuleInterop": true,
    "forceConsistentCasingInFileNames": true,
    "strict": true,
    "skipLibCheck": true,
    "resolveJsonModule": true,
    "outDir": "./dist",
    "declaration": true
  },
  "include": [
    "./scripts",
    "./test",
    "./typechain-types"
  ],
  "files": [
    "./hardhat.config.ts"
  ]
}

Type-Safe Contract Interaction

After npx hardhat compile, TypeChain generates types in typechain-types/:

import { Token } from "../typechain-types";

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

  async function deployFixture() {
    const Token = await ethers.getContractFactory("Token");
    token = await Token.deploy(ethers.parseEther("1000000"));
    return { token };
  }
});

The Token type provides autocomplete for all contract methods with proper argument and return types.

Importing Artifacts

import TokenArtifact from "../artifacts/contracts/Token.sol/Token.json";

const token = new ethers.Contract(address, TokenArtifact.abi, signer);

Plugin Ecosystem

Essential Plugins

Installing a Plugin

npm install --save-dev @openzeppelin/hardhat-upgrades @openzeppelin/contracts

// hardhat.config.ts
import "@openzeppelin/hardhat-upgrades";

All plugins are activated by importing them in hardhat.config.ts. No other registration needed.

Common Patterns

Environment Variable Handling

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

dotenv.config();

function getRequiredEnv(key: string): string {
  const value = process.env[key];
  if (!value) {
    throw new Error(`Missing required environment variable: ${key}`);
  }
  return value;
}

const config: HardhatUserConfig = {
  solidity: "0.8.27",
  networks: {
    mainnet: {
      url: getRequiredEnv("MAINNET_RPC_URL"),
      accounts: [getRequiredEnv("DEPLOYER_PRIVATE_KEY")],
    },
  },
};

export default config;

Contract Size Check

npm install --save-dev hardhat-contract-sizer

// hardhat.config.ts
import "hardhat-contract-sizer";

const config: HardhatUserConfig = {
  contractSizer: {
    alphaSort: true,
    runOnCompile: true,
    disambiguatePaths: false,
    strict: true, // fail if any contract exceeds 24KB
  },
};

Parallel Test Execution

npx hardhat test --parallel

Tests must be isolated (use loadFixture) for parallel execution. Shared mutable state between tests will cause flaky failures.

Hardhat vs Foundry

Use Hardhat when: TypeScript integration matters, complex deployment orchestration, large plugin ecosystem needed, team knows JS/TS better than Solidity.

Use Foundry when: Speed matters, fuzz testing needed, team prefers Solidity-native tooling.

Both can coexist in the same project with hardhat-foundry plugin.

Reference

• Official Docs: https://hardhat.org/docs
• Hardhat Ignition: https://hardhat.org/ignition
• GitHub: https://github.com/NomicFoundation/hardhat
• Plugin Directory: https://hardhat.org/hardhat-runner/plugins
• Hardhat Network Reference: https://hardhat.org/hardhat-network/docs/reference
• ethers v6 Docs: https://docs.ethers.org/v6/