git:20260307.47a5dbc to git:20260522.be57c0b

---

name: defi-protocol-templates

description: Implement DeFi protocols with production-ready templates for staking, AMMs, governance, and lending systems. Use when building decentralized finance applications or smart contract protocols.

---

# 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event Withdrawn(address indexed user, uint256 amount);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;

}

}

```