@openzeppelin/contracts

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.

README

A library for secure smart contract development. Build on a solid foundation of community-vetted code.

• Implementations of standards like ERC20 and ERC721.
• Flexible role-based permissioning scheme.
• Reusable Solidity components to build custom contracts and complex decentralized systems.

: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.

Overview

Installation

$ npm install @openzeppelin/contracts

OpenZeppelin Contracts features a stable API, which means that your contracts won't break unexpectedly when upgrading to a newer minor version.

An alternative to npm is to use the GitHub repository (openzeppelin/openzeppelin-contracts) to retrieve the contracts. When doing this, make sure to specify the tag for a release such as v4.5.0, instead of using the master branch.

Usage

Once installed, you can use the contracts in the library by importing them:

pragma solidity ^0.8.0;

import "@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.
• Gas Station Network: let your users interact with your contracts without having to pay for gas themselves.
• 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.

• The Hitchhiker’s Guide to Smart Contracts in Ethereum will help you get an overview of the various tools available for smart contract development, and help you set up your environment.
• A Gentle Introduction to Ethereum Programming, Part 1 provides very useful information on an introductory level, including many basic concepts from the Ethereum platform.
• For a more in-depth dive, you may read the guide Designing the Architecture for Your Ethereum Application, which discusses how to better structure your application and its relationship to the real world.

Security

This project is maintained by OpenZeppelin, and developed following our high standards for code quality and security. OpenZeppelin Contracts is meant to provide tested and community-audited code, but please use common sense when doing anything that deals with real money! We take no responsibility for your implementation decisions and any security problems you might experience.

The core development principles and strategies that OpenZeppelin Contracts is based on include: security in depth, simple and modular code, clarity-driven naming conventions, comprehensive unit testing, pre-and-post-condition sanity checks, code consistency, and regular audits.

The latest audit was done on October 2018 on version 2.0.0.

We have a bug bounty program on Immunefi. Please report any security issues you find through the Immunefi dashboard, or reach out to [e-mail].

Critical bug fixes will be backported to past major releases.

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.

Changelog

4.8.1 (2023-01-12)

• ERC4626: Use staticcall instead of call when fetching underlying ERC-20 decimals. (#3943)