@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.
$ npm install @openzeppelin/contracts
OpenZeppelin Contracts features a stable API, which means your contracts won't break unexpectedly when upgrading to a newer minor version.
Once installed, you can use the contracts in the library by importing them:
pragma solidity ^0.6.0;
import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
contract MyCollectible is ERC721 {
constructor() ERC721("MyCollectible", "MCO") public {
}
}
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 docs 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, some of the referenced tools have changed as the tooling in the ecosystem continues to rapidly evolve.
This project is maintained by OpenZeppelin, and developed following our high standards for code quality and security. OpenZeppelin 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 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.
Please report any security issues you find to security@openzeppelin.org.
OpenZeppelin exists thanks to its contributors. There are many ways you can participate and help build high quality software. Check out the contribution guide!
OpenZeppelin is released under the MIT License.
3.2.0 (2020-09-10)
Aside from upgrading them from Solidity 0.5 to 0.6, we've changed a few minor things from the proxy contracts as they were found in OpenZeppelin SDK.
UpgradeabilityProxy was renamed to UpgradeableProxy.AdminUpgradeabilityProxy was renamed to TransparentUpgradeableProxy.Proxy._willFallback was renamed to Proxy._beforeFallback.UpgradeabilityProxy._setImplementation and AdminUpgradeabilityProxy._setAdmin were made private.Address.isContract: switched from extcodehash to extcodesize for less gas usage. (#2311)ERC20Snapshot: switched to using _beforeTokenTransfer hook instead of overriding ERC20 operations. (#2312)This small change in the way we implemented ERC20Snapshot may affect users who are combining this contract with
other ERC20 flavors, since it no longer overrides _transfer, _mint, and _burn. This can result in having to remove Solidity override(...) specifiers in derived contracts for these functions, and to instead have to add it for _beforeTokenTransfer. See Using Hooks in the documentation.
FAQs
Secure Smart Contract library for Solidity
The npm package @openzeppelin/contracts receives a total of 217,491 weekly downloads. As such, @openzeppelin/contracts popularity was classified as popular.
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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