Contracts

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

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, Truffle (npm)

$ npm install @openzeppelin/contracts

Foundry (git)

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.
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:

// contracts/MyNFT.sol
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import {ERC721} from "@openzeppelin/contracts/token/ERC721/ERC721.sol";

contract MyNFT is ERC721 {
    constructor() ERC721("MyNFT", "MNFT") {
    }
}
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.

Security

Please report any security issues you find via our bug bounty program on Immunefi or directly to security@openzeppelin.org.

The Security Center contains more details about the secure development process.

Learn More

The guides in the sidebar 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 tradable assets or collectibles, like the well known ERC20 and ERC721 standards.

  • 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' 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.

Wizard →