Source: wshobson/agents Original Plugin: blockchain-web3

DeFi Protocol Templates

Production-ready templates for common DeFi protocols including staking, AMMs, governance, lending, and flash loans.

When to Use This Skill

Building staking platforms with reward distribution
Implementing AMM (Automated Market Maker) protocols
Creating governance token systems
Developing lending/borrowing protocols
Integrating flash loan functionality
Launching yield farming platforms

Staking Contract

SOLIDITY

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "@openzeppelin/contracts/security/ReentrancyGuard.sol";
import "@openzeppelin/contracts/access/Ownable.sol";

contract StakingRewards is ReentrancyGuard, Ownable {
    IERC20 public stakingToken;
    IERC20 public rewardsToken;

    uint256 public rewardRate = 100; // Rewards per second
    uint256 public lastUpdateTime;
    uint256 public rewardPerTokenStored;

    mapping(address => uint256) public userRewardPerTokenPaid;
    mapping(address => uint256) public rewards;
    mapping(address => uint256) public balances;

    uint256 private _totalSupply;

    event Staked(address indexed user, uint256 amount);
    event Withdrawn(address indexed user, uint256 amount);
    event RewardPaid(address indexed user, uint256 reward);

    constructor(address _stakingToken, address _rewardsToken) {
        stakingToken = IERC20(_stakingToken);
        rewardsToken = IERC20(_rewardsToken);
    }

    modifier updateReward(address account) {
        rewardPerTokenStored = rewardPerToken();
        lastUpdateTime = block.timestamp;

        if (account != address(0)) {
            rewards[account] = earned(account);
            userRewardPerTokenPaid[account] = rewardPerTokenStored;
        }
        _;
    }

    function rewardPerToken() public view returns (uint256) {
        if (_totalSupply == 0) {
            return rewardPerTokenStored;
        }
        return rewardPerTokenStored +
            ((block.timestamp - lastUpdateTime) * rewardRate * 1e18) / _totalSupply;
    }

    function earned(address account) public view returns (uint256) {
        return (balances[account] *
            (rewardPerToken() - userRewardPerTokenPaid[account])) / 1e18 +
            rewards[account];
    }

    function stake(uint256 amount) external nonReentrant updateReward(msg.sender) {
        require(amount > 0, "Cannot stake 0");
        _totalSupply += amount;
        balances[msg.sender] += amount;
        stakingToken.transferFrom(msg.sender, address(this), amount);
        emit Staked(msg.sender, amount);
    }

    function withdraw(uint256 amount) public nonReentrant updateReward(msg.sender) {
        require(amount > 0, "Cannot withdraw 0");
        _totalSupply -= amount;
        balances[msg.sender] -= amount;
        stakingToken.transfer(msg.sender, amount);
        emit Withdrawn(msg.sender, amount);
    }

    function getReward() public nonReentrant updateReward(msg.sender) {
        uint256 reward = rewards[msg.sender];
        if (reward > 0) {
            rewards[msg.sender] = 0;
            rewardsToken.transfer(msg.sender, reward);
            emit RewardPaid(msg.sender, reward);
        }
    }

    function exit() external {
        withdraw(balances[msg.sender]);
        getReward();
    }
}

AMM (Automated Market Maker)

SOLIDITY

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";

contract SimpleAMM {
    IERC20 public token0;
    IERC20 public token1;

    uint256 public reserve0;
    uint256 public reserve1;

    uint256 public totalSupply;
    mapping(address => uint256) public balanceOf;

    event Mint(address indexed to, uint256 amount);
    event Burn(address indexed from, uint256 amount);
    event Swap(address indexed trader, uint256 amount0In, uint256 amount1In, uint256 amount0Out, uint256 amount1Out);

    constructor(address _token0, address _token1) {
        token0 = IERC20(_token0);
        token1 = IERC20(_token1);
    }

    function addLiquidity(uint256 amount0, uint256 amount1) external returns (uint256 shares) {
        token0.transferFrom(msg.sender, address(this), amount0);
        token1.transferFrom(msg.sender, address(this), amount1);

        if (totalSupply == 0) {
            shares = sqrt(amount0 * amount1);
        } else {
            shares = min(
                (amount0 * totalSupply) / reserve0,
                (amount1 * totalSupply) / reserve1
            );
        }

        require(shares > 0, "Shares = 0");
        _mint(msg.sender, shares);
        _update(
            token0.balanceOf(address(this)),
            token1.balanceOf(address(this))
        );

        emit Mint(msg.sender, shares);
    }

    function removeLiquidity(uint256 shares) external returns (uint256 amount0, uint256 amount1) {
        uint256 bal0 = token0.balanceOf(address(this));
        uint256 bal1 = token1.balanceOf(address(this));

        amount0 = (shares * bal0) / totalSupply;
        amount1 = (shares * bal1) / totalSupply;

        require(amount0 > 0 && amount1 > 0, "Amount0 or amount1 = 0");

        _burn(msg.sender, shares);
        _update(bal0 - amount0, bal1 - amount1);

        token0.transfer(msg.sender, amount0);
        token1.transfer(msg.sender, amount1);

        emit Burn(msg.sender, shares);
    }

    function swap(address tokenIn, uint256 amountIn) external returns (uint256 amountOut) {
        require(tokenIn == address(token0) || tokenIn == address(token1), "Invalid token");

        bool isToken0 = tokenIn == address(token0);
        (IERC20 tokenIn_, IERC20 tokenOut, uint256 resIn, uint256 resOut) = isToken0
            ? (token0, token1, reserve0, reserve1)
            : (token1, token0, reserve1, reserve0);

        tokenIn_.transferFrom(msg.sender, address(this), amountIn);

        // 0.3% fee
        uint256 amountInWithFee = (amountIn * 997) / 1000;
        amountOut = (resOut * amountInWithFee) / (resIn + amountInWithFee);

        tokenOut.transfer(msg.sender, amountOut);

        _update(
            token0.balanceOf(address(this)),
            token1.balanceOf(address(this))
        );

        emit Swap(msg.sender, isToken0 ? amountIn : 0, isToken0 ? 0 : amountIn, isToken0 ? 0 : amountOut, isToken0 ? amountOut : 0);
    }

    function _mint(address to, uint256 amount) private {
        balanceOf[to] += amount;
        totalSupply += amount;
    }

    function _burn(address from, uint256 amount) private {
        balanceOf[from] -= amount;
        totalSupply -= amount;
    }

    function _update(uint256 res0, uint256 res1) private {
        reserve0 = res0;
        reserve1 = res1;
    }

    function sqrt(uint256 y) private pure returns (uint256 z) {
        if (y > 3) {
            z = y;
            uint256 x = y / 2 + 1;
            while (x < z) {
                z = x;
                x = (y / x + x) / 2;
            }
        } else if (y != 0) {
            z = 1;
        }
    }

    function min(uint256 x, uint256 y) private pure returns (uint256) {
        return x <= y ? x : y;
    }
}

Governance Token

SOLIDITY

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Votes.sol";
import "@openzeppelin/contracts/access/Ownable.sol";

contract GovernanceToken is ERC20Votes, Ownable {
    constructor() ERC20("Governance Token", "GOV") ERC20Permit("Governance Token") {
        _mint(msg.sender, 1000000 * 10**decimals());
    }

    function _afterTokenTransfer(
        address from,
        address to,
        uint256 amount
    ) internal override(ERC20Votes) {
        super._afterTokenTransfer(from, to, amount);
    }

    function _mint(address to, uint256 amount) internal override(ERC20Votes) {
        super._mint(to, amount);
    }

    function _burn(address account, uint256 amount) internal override(ERC20Votes) {
        super._burn(account, amount);
    }
}

contract Governor is Ownable {
    GovernanceToken public governanceToken;

    struct Proposal {
        uint256 id;
        address proposer;
        string description;
        uint256 forVotes;
        uint256 againstVotes;
        uint256 startBlock;
        uint256 endBlock;
        bool executed;
        mapping(address => bool) hasVoted;
    }

    uint256 public proposalCount;
    mapping(uint256 => Proposal) public proposals;

    uint256 public votingPeriod = 17280; // ~3 days in blocks
    uint256 public proposalThreshold = 100000 * 10**18;

    event ProposalCreated(uint256 indexed proposalId, address proposer, string description);
    event VoteCast(address indexed voter, uint256 indexed proposalId, bool support, uint256 weight);
    event ProposalExecuted(uint256 indexed proposalId);

    constructor(address _governanceToken) {
        governanceToken = GovernanceToken(_governanceToken);
    }

    function propose(string memory description) external returns (uint256) {
        require(
            governanceToken.getPastVotes(msg.sender, block.number - 1) >= proposalThreshold,
            "Proposer votes below threshold"
        );

        proposalCount++;
        Proposal storage newProposal = proposals[proposalCount];
        newProposal.id = proposalCount;
        newProposal.proposer = msg.sender;
        newProposal.description = description;
        newProposal.startBlock = block.number;
        newProposal.endBlock = block.number + votingPeriod;

        emit ProposalCreated(proposalCount, msg.sender, description);
        return proposalCount;
    }

    function vote(uint256 proposalId, bool support) external {
        Proposal storage proposal = proposals[proposalId];
        require(block.number >= proposal.startBlock, "Voting not started");
        require(block.number <= proposal.endBlock, "Voting ended");
        require(!proposal.hasVoted[msg.sender], "Already voted");

        uint256 weight = governanceToken.getPastVotes(msg.sender, proposal.startBlock);
        require(weight > 0, "No voting power");

        proposal.hasVoted[msg.sender] = true;

        if (support) {
            proposal.forVotes += weight;
        } else {
            proposal.againstVotes += weight;
        }

        emit VoteCast(msg.sender, proposalId, support, weight);
    }

    function execute(uint256 proposalId) external {
        Proposal storage proposal = proposals[proposalId];
        require(block.number > proposal.endBlock, "Voting not ended");
        require(!proposal.executed, "Already executed");
        require(proposal.forVotes > proposal.againstVotes, "Proposal failed");

        proposal.executed = true;

        // Execute proposal logic here

        emit ProposalExecuted(proposalId);
    }
}

Flash Loan

SOLIDITY

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";

interface IFlashLoanReceiver {
    function executeOperation(
        address asset,
        uint256 amount,
        uint256 fee,
        bytes calldata params
    ) external returns (bool);
}

contract FlashLoanProvider {
    IERC20 public token;
    uint256 public feePercentage = 9; // 0.09% fee

    event FlashLoan(address indexed borrower, uint256 amount, uint256 fee);

    constructor(address _token) {
        token = IERC20(_token);
    }

    function flashLoan(
        address receiver,
        uint256 amount,
        bytes calldata params
    ) external {
        uint256 balanceBefore = token.balanceOf(address(this));
        require(balanceBefore >= amount, "Insufficient liquidity");

        uint256 fee = (amount * feePercentage) / 10000;

        // Send tokens to receiver
        token.transfer(receiver, amount);

        // Execute callback
        require(
            IFlashLoanReceiver(receiver).executeOperation(
                address(token),
                amount,
                fee,
                params
            ),
            "Flash loan failed"
        );

        // Verify repayment
        uint256 balanceAfter = token.balanceOf(address(this));
        require(balanceAfter >= balanceBefore + fee, "Flash loan not repaid");

        emit FlashLoan(receiver, amount, fee);
    }
}

// Example flash loan receiver
contract FlashLoanReceiver is IFlashLoanReceiver {
    function executeOperation(
        address asset,
        uint256 amount,
        uint256 fee,
        bytes calldata params
    ) external override returns (bool) {
        // Decode params and execute arbitrage, liquidation, etc.
        // ...

        // Approve repayment
        IERC20(asset).approve(msg.sender, amount + fee);

        return true;
    }
}

Resources

references/staking.md: Staking mechanics and reward distribution
references/liquidity-pools.md: AMM mathematics and pricing
references/governance-tokens.md: Governance and voting systems
references/lending-protocols.md: Lending/borrowing implementation
references/flash-loans.md: Flash loan security and use cases
assets/staking-contract.sol: Production staking template
assets/amm-contract.sol: Full AMM implementation
assets/governance-token.sol: Governance system
assets/lending-protocol.sol: Lending platform template

Best Practices

Use Established Libraries: OpenZeppelin, Solmate
Test Thoroughly: Unit tests, integration tests, fuzzing
Audit Before Launch: Professional security audits
Start Simple: MVP first, add features incrementally
Monitor: Track contract health and user activity
Upgradability: Consider proxy patterns for upgrades
Emergency Controls: Pause mechanisms for critical issues

Common DeFi Patterns

Time-Weighted Average Price (TWAP): Price oracle resistance
Liquidity Mining: Incentivize liquidity provision
Vesting: Lock tokens with gradual release
Multisig: Require multiple signatures for critical operations
Timelocks: Delay execution of governance decisions