What is metamask-extension?

metamask/metamask-extension — explained in plain English

Analysis updated 2026-06-24

★ 13,120TypeScriptAudience · developerComplexity · 4/5Setup · hard

Mindmap

mindmap
  root((repo))
    What it does
      Ethereum wallet
      Transaction signing
      Dapp connector
    Features
      Crypto storage
      Approval prompts
      Private key safety
    Tech
      TypeScript
      Node 24
      Yarn Corepack
    Supported Browsers
      Chrome
      Firefox
      Chromium based

mindmap root((repo)) What it does Ethereum wallet Transaction signing Dapp connector Features Crypto storage Approval prompts Private key safety Tech TypeScript Node 24 Yarn Corepack Supported Browsers Chrome Firefox Chromium based

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What do people build with it?

USE CASE 1

Build and run a local development version of MetaMask to contribute a bug fix or new feature

USE CASE 2

Understand how a browser wallet communicates with decentralized apps by reading the extension source code

USE CASE 3

Fork MetaMask as a starting point for building a custom Ethereum wallet browser extension

What is it built with?

TypeScriptJavaScriptNode.jsYarnReact

How does it compare?

	metamask/metamask-extension	juice-shop/juice-shop	typestrong/ts-node
Stars	13,120	13,120	13,134
Language	TypeScript	TypeScript	TypeScript
Setup difficulty	hard	easy	easy
Complexity	4/5	2/5	2/5
Audience	developer	developer	developer

Figures from each repo's GitHub metadata at analysis time.

How do you get it running?

Difficulty · hard Time to first run · 1h+

Requires Node 24, Yarn via Corepack, and an Infura API key to build and run locally.

So what is it?

MetaMask is a browser extension that acts as a wallet for Ethereum and other compatible blockchains. You install it in Chrome, Firefox, or another Chromium-based browser, and it gives you a way to store cryptocurrency, connect to decentralized applications (dapps), and sign transactions directly from your browser without going through a centralized exchange. When you visit a dapp, the website can ask MetaMask to show a prompt asking you to approve a transaction or sign a message. MetaMask sits between the website and the blockchain: the website requests an action, MetaMask shows you what is being asked, and you decide whether to approve or reject. Your private keys stay in the extension and are never sent to the website. This repository is the source code for that browser extension. It is written in TypeScript and JavaScript, built using Node.js and Yarn, and compiled into a distributable package you load into your browser as an unpacked extension. The README covers how to build it locally or spin up a development environment in GitHub Codespaces. Building requires Node 24, a Yarn setup via Corepack, and an Infura API key (Infura is a service that provides access to Ethereum nodes without running your own). The official release is available from metamask.io and the browser extension stores. This GitHub repository is where contributors submit bug fixes and new features. The project has separate documentation sites for end users, developers building dapps, and contributors working on the extension itself.

Copy-paste prompts

Prompt 1

Walk me through setting up a local build of the MetaMask browser extension using Node 24 and Yarn via Corepack, what commands do I run and how do I load it as an unpacked extension in Chrome?

Prompt 2

How do I get an Infura API key and configure it for a local MetaMask development build?

Prompt 3

I want to add support for a new blockchain network in the MetaMask extension, which source files do I need to change?

Prompt 4

How does MetaMask keep private keys safe inside the browser extension and prevent websites from accessing them directly?

Frequently asked questions