What is @openzeppelin/contracts?
@openzeppelin/contracts is a library for secure smart contract development. It provides implementations of standards like ERC20 and ERC721, as well as utilities for common tasks such as access control and upgradeability.
What are @openzeppelin/contracts's main functionalities?
ERC20 Token
This code demonstrates how to create an ERC20 token using the @openzeppelin/contracts library. The ERC20 contract is imported and extended to create a new token with an initial supply.
const { ERC20 } = require('@openzeppelin/contracts/token/ERC20/ERC20.sol');
contract MyToken is ERC20 {
constructor(uint256 initialSupply) ERC20("MyToken", "MTK") {
_mint(msg.sender, initialSupply);
}
}
ERC721 Token
This code demonstrates how to create an ERC721 non-fungible token (NFT) using the @openzeppelin/contracts library. The ERC721 contract is imported and extended to create a new NFT with a minting function.
const { ERC721 } = require('@openzeppelin/contracts/token/ERC721/ERC721.sol');
contract MyNFT is ERC721 {
constructor() ERC721("MyNFT", "MNFT") {
}
function mint(address to, uint256 tokenId) public {
_mint(to, tokenId);
}
}
Access Control
This code demonstrates how to use the Ownable contract from the @openzeppelin/contracts library to restrict access to certain functions. The onlyOwner modifier ensures that only the contract owner can call the restrictedFunction.
const { Ownable } = require('@openzeppelin/contracts/access/Ownable.sol');
contract MyContract is Ownable {
function restrictedFunction() public onlyOwner {
// restricted logic
}
}
Upgradeability
This code demonstrates how to use the TransparentUpgradeableProxy contract from the @openzeppelin/contracts library to create upgradeable smart contracts. The proxy pattern allows for the logic of the contract to be upgraded while preserving the contract's state.
const { TransparentUpgradeableProxy } = require('@openzeppelin/contracts/proxy/transparent/TransparentUpgradeableProxy.sol');
contract MyContractV1 {
uint256 public value;
function setValue(uint256 _value) public {
value = _value;
}
}
contract MyContractV2 {
uint256 public value;
function setValue(uint256 _value) public {
value = _value * 2;
}
}
Other packages similar to @openzeppelin/contracts
solidity-rlp
solidity-rlp is a library for encoding and decoding RLP (Recursive Length Prefix) data in Solidity. While it focuses on a specific encoding format, @openzeppelin/contracts provides a broader range of utilities and standard implementations for smart contract development.
truffle
Truffle is a development environment, testing framework, and asset pipeline for Ethereum. While Truffle provides tools for developing and testing smart contracts, @openzeppelin/contracts offers a library of secure and reusable smart contract components.
hardhat
Hardhat is a development environment to compile, deploy, test, and debug Ethereum software. Similar to Truffle, it focuses on the development workflow, whereas @openzeppelin/contracts provides pre-built smart contract components.
[!NOTE]
Version 5.0 is currently in release candidate period. Bug bounty rewards are boosted 50% until the release.
See more details on Immunefi.
A library for secure smart contract development. Build on a solid foundation of community-vetted code.
:mage: Not sure how to get started? Check out Contracts Wizard — an interactive smart contract generator.
:building_construction: Want to scale your decentralized application? Check out OpenZeppelin Defender — a secure platform for automating and monitoring your operations.
[!IMPORTANT]
OpenZeppelin Contracts uses semantic versioning to communicate backwards compatibility of its API and storage layout. For upgradeable contracts, the storage layout of different major versions should be assumed incompatible, for example, it is unsafe to upgrade from 4.9.3 to 5.0.0. Learn more at Backwards Compatibility.
Overview
Installation
Hardhat, Truffle (npm)
$ npm install @openzeppelin/contracts
Foundry (git)
[!WARNING]
When installing via git, it is a common error to use the master
branch. This is a development branch that should be avoided in favor of tagged releases. The release process involves security measures that the master
branch does not guarantee.
[!WARNING]
Foundry installs the latest version initially, but subsequent forge update
commands will use the master
branch.
$ forge install OpenZeppelin/openzeppelin-contracts
Add @openzeppelin/contracts/=lib/openzeppelin-contracts/contracts/
in remappings.txt.
Usage
Once installed, you can use the contracts in the library by importing them:
pragma solidity ^0.8.20;
import {ERC721} from "@openzeppelin/contracts/token/ERC721/ERC721.sol";
contract MyCollectible is ERC721 {
constructor() ERC721("MyCollectible", "MCO") {
}
}
If you're new to smart contract development, head to Developing Smart Contracts to learn about creating a new project and compiling your contracts.
To keep your system secure, you should always use the installed code as-is, and neither copy-paste it from online sources nor modify it yourself. The library is designed so that only the contracts and functions you use are deployed, so you don't need to worry about it needlessly increasing gas costs.
Learn More
The guides in the documentation site will teach about different concepts, and how to use the related contracts that OpenZeppelin Contracts provides:
- Access Control: decide who can perform each of the actions on your system.
- Tokens: create tradeable assets or collectives, and distribute them via Crowdsales.
- Utilities: generic useful tools including non-overflowing math, signature verification, and trustless paying systems.
The full API is also thoroughly documented, and serves as a great reference when developing your smart contract application. You can also ask for help or follow Contracts's development in the community forum.
Finally, you may want to take a look at the guides on our blog, which cover several common use cases and good practices. The following articles provide great background reading, though please note that some of the referenced tools have changed, as the tooling in the ecosystem continues to rapidly evolve.
Security
This project is maintained by OpenZeppelin with the goal of providing a secure and reliable library of smart contract components for the ecosystem. We address security through risk management in various areas such as engineering and open source best practices, scoping and API design, multi-layered review processes, and incident response preparedness.
The OpenZeppelin Contracts Security Center contains more details about the secure development process.
The security policy is detailed in SECURITY.md
as well, and specifies how you can report security vulnerabilities, which versions will receive security patches, and how to stay informed about them. We run a bug bounty program on Immunefi to reward the responsible disclosure of vulnerabilities.
The engineering guidelines we follow to promote project quality can be found in GUIDELINES.md
.
Past audits can be found in audits/
.
Smart contracts are a nascent technology and carry a high level of technical risk and uncertainty. Although OpenZeppelin is well known for its security audits, using OpenZeppelin Contracts is not a substitute for a security audit.
OpenZeppelin Contracts is made available under the MIT License, which disclaims all warranties in relation to the project and which limits the liability of those that contribute and maintain the project, including OpenZeppelin. As set out further in the Terms, you acknowledge that you are solely responsible for any use of OpenZeppelin Contracts and you assume all risks associated with any such use.
Contribute
OpenZeppelin Contracts exists thanks to its contributors. There are many ways you can participate and help build high quality software. Check out the contribution guide!
License
OpenZeppelin Contracts is released under the MIT License.
Legal
Your use of this Project is governed by the terms found at www.openzeppelin.com/tos (the "Terms").