@openzeppelin/contracts
Advanced tools
@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.
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;
}
}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 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 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.
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.
$ 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.
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.
The guides in the documentation site will teach about different concepts, and how to use the related contracts that OpenZeppelin Contracts provides:
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.
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 security policy is detailed in SECURITY.md, 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.
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!
OpenZeppelin Contracts is released under the MIT License.
Your use of this Project is governed by the terms found at www.openzeppelin.com/tos (the "Terms").
FAQs
Secure Smart Contract library for Solidity
We found that @openzeppelin/contracts demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 4 open source maintainers collaborating on the project.
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