@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 mission-critical developer security platform to code, audit, deploy, monitor, and operate with confidence.

[!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 (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.

• 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 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").

Changelog

5.2.0 (2025-01-08)

Breaking Changes

Custom error changes

This version comes with changes to the custom error identifiers. Contracts previously depending on the following errors should be replaced accordingly:

• Replace Errors.FailedCall with a bubbled-up revert reason in Address.sendValue.

Changes by category

General

• Update some pragma directives to ensure that all file requirements match that of the files they import. (#5273)

Account

• ERC4337Utils: Add a reusable library to manipulate user operations and interact with ERC-4337 contracts (#5274)
• ERC7579Utils: Add a reusable library to interact with ERC-7579 modular accounts (#5274)

Governance

• GovernorCountingOverridable: Add a governor counting module that enables token holders to override the vote of their delegate. (#5192)
• VotesExtended: Create an extension of Votes which checkpoints balances and delegates. (#5192)

Proxy

• Clones: Add cloneWithImmutableArgs and cloneDeterministicWithImmutableArgs variants that create clones with per-instance immutable arguments. The immutable arguments can be retrieved using fetchCloneArgs. The corresponding predictDeterministicWithImmutableArgs function is also included. (#5109)

Tokens

• ERC1363Utils: Add helper similar to the existing ERC721Utils and ERC1155Utils (#5133)

Utils

• Address: bubble up revert data on sendValue failed call (#5418)
• Bytes: Add a library of common operations that operate on bytes objects. (#5252)
• CAIP2 and CAIP10: Add libraries for formatting and parsing CAIP-2 and CAIP-10 identifiers. (#5252)
• NoncesKeyed: Add a variant of Nonces that implements the ERC-4337 entrypoint nonce system. (#5272)
• Packing: Add variants for packing bytes10 and bytes22 (#5274)
• Strings: Add parseUint, parseInt, parseHexUint and parseAddress to parse strings into numbers and addresses. Also provide variants of these functions that parse substrings, and tryXxx variants that do not revert on invalid input. (#5166)