@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

5.1.0 (2024-10-17)

Breaking changes

• ERC1967Utils: Removed duplicate declaration of the Upgraded, AdminChanged and BeaconUpgraded events. These events are still available through the IERC1967 interface located under the contracts/interfaces/ directory. Minimum pragma version is now 0.8.21.
• Governor, GovernorCountingSimple: The _countVote virtual function now returns an uint256 with the total votes casted. This change allows for more flexibility for partial and fractional voting. Upgrading users may get a compilation error that can be fixed by adding a return statement to the _countVote function.

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 Address.FailedInnerCall with Errors.FailedCall
• Replace Address.AddressInsufficientBalance with Errors.InsufficientBalance
• Replace Clones.Create2InsufficientBalance with Errors.InsufficientBalance
• Replace Clones.ERC1167FailedCreateClone with Errors.FailedDeployment
• Replace Clones.Create2FailedDeployment with Errors.FailedDeployment
• SafeERC20: Replace Address.AddressEmptyCode with SafeERC20FailedOperation if there is no code at the token's address.
• SafeERC20: Replace generic Error(string) with SafeERC20FailedOperation if the returned data can't be decoded as bool.
• SafeERC20: Replace generic SafeERC20FailedOperation with the revert message from the contract call if it fails.

Changes by category

General

• AccessManager, VestingWallet, TimelockController and ERC2771Forwarder: Added a public initializer function in their corresponding upgradeable variants. (#5008)

Access

• AccessControlEnumerable: Add a getRoleMembers method to return all accounts that have role. (#4546)
• AccessManager: Allow the onlyAuthorized modifier to restrict functions added to the manager. (#5014)

Finance

• VestingWalletCliff: Add an extension of the VestingWallet contract with an added cliff. (#4870)

Governance

• GovernorCountingFractional: Add a governor counting module that allows distributing voting power amongst 3 options (For, Against, Abstain). (#5045)
• Votes: Set _moveDelegateVotes visibility to internal instead of private. (#5007)

Proxy

• Clones: Add version of clone and cloneDeterministic that support sending value at creation. (#4936)
• TransparentUpgradeableProxy: Make internal _proxyAdmin() getter have view visibility. (#4688)
• ProxyAdmin: Fixed documentation for UPGRADE_INTERFACE_VERSION getter. (#5031)

Tokens

• ERC1363: Add implementation of the token payable standard allowing execution of contract code after transfers and approvals. (#4631)
• ERC20TemporaryApproval: Add an ERC-20 extension that implements temporary approval using transient storage, based on ERC7674 (draft). (#5071)
• SafeERC20: Add "relaxed" function for interacting with ERC-1363 functions in a way that is compatible with EOAs. (#4631)
• SafeERC20: Document risks of safeIncreaseAllowance and safeDecreaseAllowance when associated with ERC-7674. (#5262)
• ERC721Utils and ERC1155Utils: Add reusable libraries with functions to perform acceptance checks on IERC721Receiver and IERC1155Receiver implementers. (#4845)
• ERC1363Utils: Add helper similar to the existing ERC721Utils and ERC1155Utils. (#5133)

Utils

• Arrays: add a sort functions for address[], bytes32[] and uint256[] memory arrays. (#4846)
• Arrays: add new functions lowerBound, upperBound, lowerBoundMemory and upperBoundMemory for lookups in sorted arrays with potential duplicates. (#4842)
• Arrays: deprecate findUpperBound in favor of the new lowerBound. (#4842)
• Base64: Add encodeURL following section 5 of RFC4648 for URL encoding (#4822)
• Comparator: A library of comparator functions, useful for customizing the behavior of the Heap structure. (#5084)
• Create2: Bubbles up returndata from a deployed contract that reverted during construction. (#5052)
• Create2, Clones: Mask computeAddress and cloneDeterministic outputs to produce a clean value for an address type (i.e. only use 20 bytes) (#4941)
• Errors: New library of common custom errors. (#4936)
• Hashes: A library with commonly used hash functions. (#3617)
• Packing: Added a new utility for packing, extracting and replacing bytesXX values. (#4992)
• Panic: Add a library for reverting with panic codes. (#3298)
• ReentrancyGuardTransient: Added a variant of ReentrancyGuard that uses transient storage. (#4988)
• Strings: Added a utility function for converting an address to checksummed string. (#5067)
• SlotDerivation: Add a library of methods for derivating common storage slots. (#4975)
• TransientSlot: Add primitives for operating on the transient storage space using a typed-slot representation. (#4980)

Cryptography

• SignatureChecker: refactor isValidSignatureNow to avoid validating ECDSA signatures if there is code deployed at the signer's address. (#4951)
• MerkleProof: Add variations of verify, processProof, multiProofVerify and processMultiProof (and equivalent calldata version) with support for custom hashing functions. (#4887)
• P256: Library for verification and public key recovery of P256 (aka secp256r1) signatures. (#4881)
• RSA: Library to verify signatures according to RFC 8017 Signature Verification Operation (#4952)

Math

• Math: add an invMod function to get the modular multiplicative inverse of a number in Z/nZ. (#4839)
• Math: Add modExp function that exposes the EIP-198 precompile. Includes uint256 and bytes memory versions. (#3298)
• Math: Custom errors replaced with native panic codes. (#3298)
• Math, SignedMath: Add a branchless ternary function that computescond ? a : b in constant gas cost. (#4976)
• SafeCast: Add toUint(bool) for operating on bool values as uint256. (#4878)

Structures

• CircularBuffer: Add a data structure that stores the last N values pushed to it. (#4913)
• DoubleEndedQueue: Custom errors replaced with native panic codes. (#4872)
• EnumerableMap: add UintToBytes32Map, AddressToAddressMap, AddressToBytes32Map and Bytes32ToAddressMap. (#4843)
• Heap: A data structure that implements a heap-based priority queue. (#5084)
• MerkleTree: A data structure that allows inserting elements into a merkle tree and updating its root hash. (#3617)