💧 First Smart Contract — Faucet on Ethereum Sepolia

This is my first smart contract built and deployed with Hardhat 3, written in Solidity 0.8.28, and tested using Mocha + Chai + Ethers v6.
It implements a simple Faucet, which allows users to withdraw small amounts of ETH with a cooldown time between withdrawals.

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🧩 Overview

Contract: Faucet.sol
Network: Sepolia (chainId 11155111)
Address: 0xcAC087aF249117F2a4Ef479c528749C858D6A8a2
Deployer: 0xeC0760E041Ff8C5377cCB8d123d90D3F96d0fba9
Verified on: Blockscout

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⚙️ Smart Contract Description

Faucet.sol

A simple faucet that:

• allows anyone to fund it by sending ETH,
• allows each address to withdraw up to 0.1 ETH,
• enforces a 1-hour cooldown between withdrawals per address.

Main features

• Uses custom errors (AmountZero, AmountTooHigh, CooldownActive, InsufficientFaucetBalance) → cheaper gas than revert strings.
• Emits events:
  • Funded(address from, uint256 amount)
  • Withdraw(address to, uint256 amount)
• Safe transfer pattern with call{value: _amount} and CEI (Checks–Effects–Interactions).

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🧪 Testing

All tests are simulated locally using Hardhat’s built-in network (no real gas or ETH needed).

Run the suite:

npx hardhat test

It covers:

• ✅ Faucet funding (receive + Funded event)
• ✅ Successful withdrawals within limits
• ✅ Reverts on zero or excessive amounts
• ✅ Reverts if faucet balance is insufficient
• ✅ Cooldown logic (CooldownActive revert + success after 1h)

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🚀 Deployment

Deployment script: scripts/deploy.ts

Deploy to Sepolia

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

Expected output example:

Network: sepolia (chainId 11155111)
Faucet deployed to: 0xcAC087aF249117F2a4Ef479c528749C858D6A8a2
Deploy tx hash: 0x0359ebde17a703e77f9687fd41b70c4cc939ca6fd88fd96af334b4753ae1096c
Deploying contract with account: 0xeC0760E041Ff8C5377cCB8d123d90D3F96d0fba9

Verify on Etherscan

Make sure you have an API key in .env:

ETHERSCAN_API_KEY=your_key_here

Then run:

npx hardhat verify --network sepolia 0xcAC087aF249117F2a4Ef479c528749C858D6A8a2

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🧰 Environment Setup

Requirements

• Node.js ≥ 18
• Hardhat 3
• TypeScript
• Ethers v6

Install dependencies

npm install

Environment variables (.env)

SEPOLIA_RPC_URL=https://eth-sepolia.g.alchemy.com/v2/your-key
SEPOLIA_PRIVATE_KEY=0xabc123...   # private key of your Sepolia wallet
ETHERSCAN_API_KEY=your-etherscan-key

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🧠 Useful Hardhat Commands

Command	Description
npx hardhat compile	Compile contracts
npx hardhat test	Run test suite
npx hardhat run scripts/deploy.ts --network sepolia	Deploy to Sepolia
npx hardhat verify --network sepolia <address>	Verify on Etherscan
npx hardhat console --network sepolia	Open interactive console

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🪙 Example Usage

Fund the Faucet

Send ETH directly to the contract address:

0xcAC087aF249117F2a4Ef479c528749C858D6A8a2

Withdraw from the Faucet

Call:

withdraw(uint256 _amount)

Example: _amount = 0.05 ether

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🧑‍💻 Tech Stack

• Solidity 0.8.28
• Hardhat 3 + Ethers v6
• TypeScript
• Chai / Mocha for testing
• Dotenv for config
• Blockscout / Etherscan for verification

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🏁 Next Steps

• ✅ Add faucetBalance() public view
• 🧪 Expand test coverage for reentrancy checks
• 🌐 Deploy also to Optimism testnet
• 📜 Write a frontend DApp with Viem + React to interact with the faucet

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✨ Author

Made with ❤️ by Valentina First Smart Contract project – Ethereum Bootcamp @ Alchemy University (2025)