Extension.js

The cross-browser extension framework. Build for Chrome, Edge, Firefox, and Safari with no build config required.

npx extension@latest create my-extension
cd my-extension
npm run dev

Works with npm, pnpm, yarn, bun, and deno.

Documentation · Templates · Examples · Discord

Why Extension.js

Browser extensions ship with the worst dev experience in modern web. Manifest V3 fragmentation, browser-specific quirks, no hot reload for content scripts, and a separate build pipeline for every target. Extension.js fixes that.

• Hot Module Replacement for background, content, popup, and options scripts, including React, Vue, Svelte, and Preact components
• Manifest V3 by default, with automatic adapters for Chrome, Edge, Firefox, and Safari targets
• One CLI for Chrome, Edge, Firefox, and any Chromium or Gecko binary
• Zero config, no webpack, no rollup, no plugins to maintain
• First-class TypeScript, React, Vue, Svelte, and Preact support
• Production builds with extension build --zip, ready for the Chrome Web Store and Firefox Add-ons
• Drop-in for existing extensions with one devDependency

Watch it work

Or skip the install and try a live template in your browser.

How is this different

If you have used Plasmo, WXT, or CRXJS, here is what Extension.js does that the others do not:

Capability	Extension.js
Run any GitHub sample directly	extension dev https://github.com/.../sample
Managed browser binaries	extension install firefox downloads an isolated build
Cross-browser HMR for content scripts	Built in, no plugin glue
Production zip for the stores	extension build --zip
Framework agnostic	Vanilla, TS, React, Vue, Svelte, Preact, no lock-in
Custom Chromium and Gecko binaries	--chromium-binary, --gecko-binary

Extension.js is sponsored by extension.dev, the platform that hosts the build, share and store submission side of shipping an extension. To hand someone an unpublished build behind a link, with no zip and no install on their side, see Share an unpublished build for review.

Frameworks

ESNext Try out	TypeScript Try out	WASM Try out	React Try out	Vue Try out	Svelte Try out	Preact Try out

Browsers

Use these flags with extension dev, extension start, or extension preview:

• Select a browser: --browser <chrome | edge | firefox | safari>
• Custom Chromium binary: --chromium-binary <path-to-binary>
• Custom Gecko (Firefox) binary: --gecko-binary <path-to-binary>

# Chrome (system default)
npx extension@latest dev --browser=chrome

# Edge
npx extension@latest dev --browser=edge

# Custom Chrome/Chromium path
npx extension@latest dev --chromium-binary "/Applications/Google Chrome.app/Contents/MacOS/Google Chrome"

# Custom Firefox path
npx extension@latest dev --gecko-binary "/Applications/Firefox.app/Contents/MacOS/firefox"

Google Chrome ✅ Supported	Microsoft Edge ✅ Supported	Mozilla Firefox ✅ Supported	Apple Safari ✅ Supported	Chromium-based ✅ Supported	Gecko-based ✅ Supported

Ship to the store

Build a production-ready bundle and zip it for submission to the Chrome Web Store, Edge Add-ons, or Firefox AMO:

# Production build
npx extension@latest build

# Production build packaged as a ZIP
npx extension@latest build --zip

# Per-browser builds
npx extension@latest build --browser=firefox --zip

Useful flags:

• --zip packages the build into a ZIP ready for store upload
• --zip-source includes source files for store source-code review
• --zip-filename <name> controls the output filename
• --polyfill enables the cross-browser webextension polyfill

Manage browser binaries

Skip the system-install dance. Extension.js can download and manage isolated browser binaries for clean dev sessions:

# Install a managed Firefox build
npx extension@latest install firefox

# Install Chrome and Edge in one go
npx extension@latest install --browser=all

# Print where managed browsers live
npx extension@latest install --where

Add to an existing extension

Install Extension.js as a dev dependency and wire up your scripts.

npm install extension@latest --save-dev

{
  "scripts": {
    "build": "extension build",
    "dev": "extension dev",
    "preview": "extension preview"
  }
}

Run npm run dev to develop, and watch the browser open with your extension already loaded:

Use npm run build for production, and npm run preview to inspect the production output.

Start from a Chrome sample

Pull any sample from Chrome Extension Samples and run it directly:

npx extension@latest dev https://github.com/GoogleChrome/chrome-extensions-samples/tree/main/functional-samples/sample.page-redder --browser=edge

Package managers

npm ✅ Supported	pnpm ✅ Supported	Yarn ✅ Supported	Bun ✅ Supported	Deno ✅ Supported

Community

• Star the repo if Extension.js helped you ship faster
• Join the Discord for help and feedback
• Open issues and feature requests on GitHub
• Browse production-ready examples

Sponsors

Sponsors help the project ship faster releases, better developer experience, and long-term reliability for extension teams.

Become a sponsor

Documentation is hosted by Mintlify through its open source program. Tiers and placement are listed in BACKERS.md.

License

MIT (c) Cezar Augusto and the Extension.js authors.