--- name: ethereum-wingman description: Ethereum development tutor and builder for Scaffold-ETH 2 projects. Triggers on "build", "create", "dApp", "smart contract", "Solidity", "DeFi", "Ethereum", "web3", or any blockchain development task. ALWAYS uses fork mode to test against real protocol state. license: MIT metadata: author: BuidlGuidl version: "2.0.0" ---

Ethereum Wingman

Comprehensive Ethereum development guide for AI agents. Covers smart contract development, DeFi protocols, security best practices, and the SpeedRun Ethereum curriculum.

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AI AGENT INSTRUCTIONS - READ THIS FIRST

Default Stack: Scaffold-ETH 2 with Fork Mode

When a user wants to BUILD any Ethereum project, follow these steps:

Step 1: Create Project

npx create-eth@latest
# Select: foundry (recommended), target chain, project name

Step 2: Fix Polling Interval

Edit packages/nextjs/scaffold.config.ts and change:

pollingInterval: 30000,  // Default: 30 seconds (way too slow!)

to:

pollingInterval: 3000,   // 3 seconds (much better for development)

Step 3: Install & Fork a Live Network

cd <project-name>
yarn install
yarn fork --network base  # or mainnet, arbitrum, optimism, polygon

Step 4: Enable Auto Block Mining (REQUIRED!)

# In a new terminal, enable interval mining (1 block/second)
cast rpc anvil_setIntervalMining 1

Without this, block.timestamp stays FROZEN and time-dependent logic breaks!

Optional: Make it permanent by editing packages/foundry/package.json to add --block-time 1 to the fork script.

Step 5: Deploy to Local Fork (FREE!)

yarn deploy

Step 6: Start Frontend

yarn start

Step 7: Test the Frontend

After the frontend is running, open a browser and test the app:

1. Navigate to http://localhost:3000
2. Take a snapshot to get page elements (burner wallet address is in header)
3. Click the faucet to fund the burner wallet with ETH
4. Transfer tokens from whales if needed (use burner address from page)
5. Click through the app to verify functionality

Use the cursor-browser-extension MCP tools for browser automation. See tools/testing/frontend-testing.md for detailed workflows.

DO NOT:

• Run yarn chain (use yarn fork --network instead!)
• Manually run forge init or set up Foundry from scratch
• Manually create Next.js projects
• Set up wallet connection manually (SE2 has RainbowKit pre-configured)

Why Fork Mode?

yarn chain (WRONG)              yarn fork --network base (CORRECT)
└─ Empty local chain            └─ Fork of real Base mainnet
└─ No protocols                 └─ Uniswap, Aave, etc. available
└─ No tokens                    └─ Real USDC, WETH exist
└─ Testing in isolation         └─ Test against REAL state

Address Data Available

Token, protocol, and whale addresses are in data/addresses/:

• tokens.json - WETH, USDC, DAI, etc. per chain
• protocols.json - Uniswap, Aave, Chainlink per chain
• whales.json - Large token holders for test funding

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THE MOST CRITICAL CONCEPT

NOTHING IS AUTOMATIC ON ETHEREUM.

Smart contracts cannot execute themselves. There is no cron job, no scheduler, no background process. For EVERY function that "needs to happen":

1. Make it callable by ANYONE (not just admin)
2. Give callers a REASON (profit, reward, their own interest)
3. Make the incentive SUFFICIENT to cover gas + profit

Always ask: "Who calls this function? Why would they pay gas?"

If you can't answer this, your function won't get called.

Examples of Proper Incentive Design

// LIQUIDATIONS: Caller gets bonus collateral
function liquidate(address user) external {
    require(getHealthFactor(user) < 1e18, "Healthy");
    uint256 bonus = collateral * 5 / 100; // 5% bonus
    collateralToken.transfer(msg.sender, collateral + bonus);
}

// YIELD HARVESTING: Caller gets % of harvest
function harvest() external {
    uint256 yield = protocol.claimRewards();
    uint256 callerReward = yield / 100; // 1%
    token.transfer(msg.sender, callerReward);
}

// CLAIMS: User wants their own tokens
function claimRewards() external {
    uint256 reward = pendingRewards[msg.sender];
    pendingRewards[msg.sender] = 0;
    token.transfer(msg.sender, reward);
}

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Critical Gotchas (Memorize These)

1. Token Decimals Vary

USDC = 6 decimals, not 18!

// BAD: Assumes 18 decimals - transfers 1 TRILLION USDC!
uint256 oneToken = 1e18;

// GOOD: Check decimals
uint256 oneToken = 10 ** token.decimals();

Common decimals:

• USDC, USDT: 6 decimals
• WBTC: 8 decimals
• Most tokens (DAI, WETH): 18 decimals

2. ERC-20 Approve Pattern Required

Contracts cannot pull tokens directly. Two-step process:

// Step 1: User approves
token.approve(spenderContract, amount);

// Step 2: Contract pulls tokens
token.transferFrom(user, address(this), amount);

Never use infinite approvals:

// DANGEROUS
token.approve(spender, type(uint256).max);

// SAFE
token.approve(spender, exactAmount);

3. No Floating Point in Solidity

Use basis points (1 bp = 0.01%):

// BAD: This equals 0
uint256 fivePercent = 5 / 100;

// GOOD: Basis points
uint256 FEE_BPS = 500; // 5% = 500 basis points
uint256 fee = (amount * FEE_BPS) / 10000;

4. Reentrancy Attacks

External calls can call back into your contract:

// SAFE: Checks-Effects-Interactions pattern
function withdraw() external nonReentrant {
    uint256 bal = balances[msg.sender];
    balances[msg.sender] = 0; // Effect BEFORE interaction
    (bool success,) = msg.sender.call{value: bal}("");
    require(success);
}

Always use OpenZeppelin's ReentrancyGuard.

5. Never Use DEX Spot Prices as Oracles

Flash loans can manipulate spot prices instantly:

// SAFE: Use Chainlink
function getPrice() internal view returns (uint256) {
    (, int256 price,, uint256 updatedAt,) = priceFeed.latestRoundData();
    require(block.timestamp - updatedAt < 3600, "Stale");
    require(price > 0, "Invalid");
    return uint256(price);
}

6. Vault Inflation Attack

First depositor can steal funds via share manipulation:

// Mitigation: Virtual offset
function convertToShares(uint256 assets) public view returns (uint256) {
    return assets.mulDiv(totalSupply() + 1e3, totalAssets() + 1);
}

7. Use SafeERC20

Some tokens (USDT) don't return bool on transfer:

import "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
using SafeERC20 for IERC20;

token.safeTransfer(to, amount); // Handles non-standard tokens

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Scaffold-ETH 2 Development

Project Structure

packages/
├── foundry/              # Smart contracts
│   ├── contracts/        # Your Solidity files
│   └── script/           # Deploy scripts
└── nextjs/
    ├── app/              # React pages
    └── contracts/        # Generated ABIs + externalContracts.ts

Essential Hooks

// Read contract data
const { data } = useScaffoldReadContract({
  contractName: "YourContract",
  functionName: "greeting",
});

// Write to contract
const { writeContractAsync } = useScaffoldWriteContract("YourContract");

// Watch events
useScaffoldEventHistory({
  contractName: "YourContract",
  eventName: "Transfer",
  fromBlock: 0n,
});

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SpeedRun Ethereum Challenges

Reference these for hands-on learning:

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