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name: blockchain-web3 description: Solidity smart contracts, Web3 development, DeFi protocols, NFTs, EVM chains, Hardhat/Foundry tooling, and blockchain security. Use when writing smart contracts, building dApps, auditing contract security, or integrating Web3 wallets.

Blockchain & Web3 Development

Smart Contract Development (Solidity)

Contract Structure

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/access/Ownable.sol";

contract MyToken is ERC20, Ownable {
    constructor() ERC20("MyToken", "MTK") Ownable(msg.sender) {
        _mint(msg.sender, 1000000 * 10 ** decimals());
    }
}

Security Patterns

• Checks-Effects-Interactions: Validate → update state → external calls
• Reentrancy guard: Use OpenZeppelin ReentrancyGuard or nonReentrant
• Access control: Ownable, AccessControl, or custom modifiers
• Integer safety: Solidity 0.8+ has built-in overflow checks
• Pull over push: Let users withdraw rather than sending funds

Common Vulnerabilities

Vulnerability	Prevention
Reentrancy	nonReentrant modifier, CEI pattern
Front-running	Commit-reveal schemes, flashbot protection
Oracle manipulation	Use Chainlink, TWAP over spot prices
Unchecked return values	Always check transfer() return or use safeTransfer
Delegatecall injection	Never delegatecall to user-supplied addresses

Development Tooling

Hardhat

npx hardhat init
npx hardhat compile
npx hardhat test
npx hardhat deploy --network sepolia

Foundry

forge init
forge build
forge test -vvv
forge script script/Deploy.s.sol --rpc-url $RPC --broadcast

Frontend Integration (ethers.js v6 / viem)

// viem (recommended for new projects)
import { createPublicClient, http } from 'viem'
import { mainnet } from 'viem/chains'

const client = createPublicClient({ chain: mainnet, transport: http() })
const balance = await client.getBalance({ address: '0x...' })

// wagmi hooks (React)
import { useAccount, useBalance, useContractWrite } from 'wagmi'
const { address } = useAccount()
const { data: balance } = useBalance({ address })

DeFi Patterns

• AMM: Constant product formula (x * y = k), concentrated liquidity
• Lending: Overcollateralized loans, liquidation mechanisms, interest rate models
• Staking: Reward distribution with rewardPerToken accumulator pattern
• Governance: Token-weighted voting, timelock controllers, proposal lifecycle

Gas Optimization

• Use calldata over memory for read-only params
• Pack structs (smaller types together for slot efficiency)
• Use unchecked blocks for safe arithmetic
• Minimize storage reads/writes (cache in memory)
• Use events instead of storage for data that doesn't need on-chain access