Openzeppelin

OpenZeppelin Contracts Skill

Expert usage of OpenZeppelin Contracts, the standard library for secure smart contract development.

Capabilities

• Access Control: Ownable, AccessControl, Governor patterns
• Upgradeable Contracts: UUPS and Transparent Proxy plugins
• Token Standards: ERC-20, ERC-721, ERC-1155 implementations
• Security Utilities: ReentrancyGuard, Pausable, SafeERC20
• Governance: Governor and TimelockController
• Metatransactions: ERC-2771 support
• Cryptographic Utilities: ECDSA, MerkleProof, EIP712

Installation

# Standard contracts
npm install @openzeppelin/contracts

# Upgradeable contracts
npm install @openzeppelin/contracts-upgradeable

# Hardhat upgrades plugin
npm install @openzeppelin/hardhat-upgrades

Access Control

Ownable

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

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

contract MyContract is Ownable {
    constructor(address initialOwner) Ownable(initialOwner) {}

    function protectedFunction() external onlyOwner {
        // Only owner can call
    }
}

AccessControl (Role-Based)

import "@openzeppelin/contracts/access/AccessControl.sol";

contract MyContract is AccessControl {
    bytes32 public constant ADMIN_ROLE = keccak256("ADMIN_ROLE");
    bytes32 public constant MINTER_ROLE = keccak256("MINTER_ROLE");
    bytes32 public constant PAUSER_ROLE = keccak256("PAUSER_ROLE");

    constructor() {
        _grantRole(DEFAULT_ADMIN_ROLE, msg.sender);
        _grantRole(ADMIN_ROLE, msg.sender);
    }

    function mint(address to, uint256 amount) external onlyRole(MINTER_ROLE) {
        // Minting logic
    }

    function pause() external onlyRole(PAUSER_ROLE) {
        // Pausing logic
    }
}

AccessControlEnumerable

import "@openzeppelin/contracts/access/extensions/AccessControlEnumerable.sol";

contract MyContract is AccessControlEnumerable {
    function getAllAdmins() external view returns (address[] memory) {
        uint256 count = getRoleMemberCount(DEFAULT_ADMIN_ROLE);
        address[] memory admins = new address[](count);
        for (uint256 i = 0; i < count; i++) {
            admins[i] = getRoleMember(DEFAULT_ADMIN_ROLE, i);
        }
        return admins;
    }
}

Token Standards

ERC-20 with Extensions

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Burnable.sol";
import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Pausable.sol";
import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Permit.sol";
import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Votes.sol";
import "@openzeppelin/contracts/access/AccessControl.sol";

contract MyToken is ERC20, ERC20Burnable, ERC20Pausable, ERC20Permit, ERC20Votes, AccessControl {
    bytes32 public constant MINTER_ROLE = keccak256("MINTER_ROLE");
    bytes32 public constant PAUSER_ROLE = keccak256("PAUSER_ROLE");

    constructor() ERC20("MyToken", "MTK") ERC20Permit("MyToken") {
        _grantRole(DEFAULT_ADMIN_ROLE, msg.sender);
        _grantRole(MINTER_ROLE, msg.sender);
        _grantRole(PAUSER_ROLE, msg.sender);
    }

    function mint(address to, uint256 amount) public onlyRole(MINTER_ROLE) {
        _mint(to, amount);
    }

    function pause() public onlyRole(PAUSER_ROLE) {
        _pause();
    }

    function unpause() public onlyRole(PAUSER_ROLE) {
        _unpause();
    }

    // Required overrides
    function _update(address from, address to, uint256 value)
        internal
        override(ERC20, ERC20Pausable, ERC20Votes)
    {
        super._update(from, to, value);
    }

    function nonces(address owner)
        public
        view
        override(ERC20Permit, Nonces)
        returns (uint256)
    {
        return super.nonces(owner);
    }
}

ERC-721 with Extensions

import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
import "@openzeppelin/contracts/token/ERC721/extensions/ERC721Enumerable.sol";
import "@openzeppelin/contracts/token/ERC721/extensions/ERC721URIStorage.sol";
import "@openzeppelin/contracts/token/ERC721/extensions/ERC721Royalty.sol";

contract MyNFT is ERC721, ERC721Enumerable, ERC721URIStorage, ERC721Royalty {
    uint256 private _tokenIdCounter;

    constructor() ERC721("MyNFT", "MNFT") {
        _setDefaultRoyalty(msg.sender, 500); // 5% royalty
    }

    function safeMint(address to, string memory uri) public {
        uint256 tokenId = _tokenIdCounter++;
        _safeMint(to, tokenId);
        _setTokenURI(tokenId, uri);
    }

    // Required overrides
    function _update(address to, uint256 tokenId, address auth)
        internal
        override(ERC721, ERC721Enumerable)
        returns (address)
    {
        return super._update(to, tokenId, auth);
    }

    function _increaseBalance(address account, uint128 value)
        internal
        override(ERC721, ERC721Enumerable)
    {
        super._increaseBalance(account, value);
    }

    function tokenURI(uint256 tokenId)
        public
        view
        override(ERC721, ERC721URIStorage)
        returns (string memory)
    {
        return super.tokenURI(tokenId);
    }

    function supportsInterface(bytes4 interfaceId)
        public
        view
        override(ERC721, ERC721Enumerable, ERC721URIStorage, ERC721Royalty)
        returns (bool)
    {
        return super.supportsInterface(interfaceId);
    }
}

Governance

Governor Setup

import "@openzeppelin/contracts/governance/Governor.sol";
import "@openzeppelin/contracts/governance/extensions/GovernorSettings.sol";
import "@openzeppelin/contracts/governance/extensions/GovernorCountingSimple.sol";
import "@openzeppelin/contracts/governance/extensions/GovernorVotes.sol";
import "@openzeppelin/contracts/governance/extensions/GovernorVotesQuorumFraction.sol";
import "@openzeppelin/contracts/governance/extensions/GovernorTimelockControl.sol";

contract MyGovernor is
    Governor,
    GovernorSettings,
    GovernorCountingSimple,
    GovernorVotes,
    GovernorVotesQuorumFraction,
    GovernorTimelockControl
{
    constructor(
        IVotes _token,
        TimelockController _timelock
    )
        Governor("MyGovernor")
        GovernorSettings(
            1 days,     // Voting delay
            1 weeks,    // Voting period
            100e18      // Proposal threshold
        )
        GovernorVotes(_token)
        GovernorVotesQuorumFraction(4) // 4% quorum
        GovernorTimelockControl(_timelock)
    {}

    // Required overrides...
}

Upgradeable Contracts

UUPS Pattern

import "@openzeppelin/contracts-upgradeable/proxy/utils/Initializable.sol";
import "@openzeppelin/contracts-upgradeable/proxy/utils/UUPSUpgradeable.sol";
import "@openzeppelin/contracts-upgradeable/access/OwnableUpgradeable.sol";

contract MyContractV1 is Initializable, UUPSUpgradeable, OwnableUpgradeable {
    uint256 public value;

    /// @custom:oz-upgrades-unsafe-allow constructor
    constructor() {
        _disableInitializers();
    }

    function initialize() public initializer {
        __Ownable_init(msg.sender);
        __UUPSUpgradeable_init();
    }

    function _authorizeUpgrade(address newImplementation)
        internal
        override
        onlyOwner
    {}
}

Deployment Script

const { ethers, upgrades } = require("hardhat");

async function main() {
  // Deploy
  const MyContract = await ethers.getContractFactory("MyContractV1");
  const proxy = await upgrades.deployProxy(MyContract, [], {
    initializer: "initialize",
    kind: "uups",
  });
  await proxy.waitForDeployment();
  console.log("Proxy:", await proxy.getAddress());

  // Upgrade
  const MyContractV2 = await ethers.getContractFactory("MyContractV2");
  await upgrades.upgradeProxy(await proxy.getAddress(), MyContractV2);
}

Security Utilities

SafeERC20

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

contract MyContract {
    using SafeERC20 for IERC20;

    function deposit(IERC20 token, uint256 amount) external {
        token.safeTransferFrom(msg.sender, address(this), amount);
    }

    function withdraw(IERC20 token, uint256 amount) external {
        token.safeTransfer(msg.sender, amount);
    }
}

ReentrancyGuard

import "@openzeppelin/contracts/utils/ReentrancyGuard.sol";

contract MyContract is ReentrancyGuard {
    function withdraw() external nonReentrant {
        // Safe from reentrancy
    }
}

MerkleProof

import "@openzeppelin/contracts/utils/cryptography/MerkleProof.sol";

contract Airdrop {
    bytes32 public merkleRoot;

    function claim(bytes32[] calldata proof, uint256 amount) external {
        bytes32 leaf = keccak256(abi.encodePacked(msg.sender, amount));
        require(MerkleProof.verify(proof, merkleRoot, leaf), "Invalid proof");
        // Process claim
    }
}

Process Integration

Best Practices

1. Always use latest stable version
2. Understand inheritance order
3. Use Wizard for starting templates
4. Audit custom extensions
5. Test upgrade paths thoroughly

See Also

• skills/solidity-dev/SKILL.md - Solidity development
• OpenZeppelin Docs
• Contracts Wizard