What is Extension.js? Introduction and overview

Build browser extensions for Chrome, Edge, and Firefox with one modern workflow. Extension.js handles manifest compilation, browser-specific output, reload behavior, and packaging. Focus on product features instead of build tooling. Use familiar web tooling like TypeScript, React, Vue, and Tailwind CSS. Keep direct access to native extension APIs.

Comparing tools? See how Extension.js compares to other frameworks in the framework comparison.

CLI version: Run extension --version (or npx extension@latest --version) for the build you are using. The extension package on npm lists the latest publish. GitHub releases track changelog-style notes without tying these docs to a specific patch number.

Video walkthrough

Choose your path

If you are…	Start here
New to browser extensions altogether	What is a browser extension? and Create your first extension
Moving fast with AI tools and templates	Templates and Get started immediately
A seasoned web developer new to extensions	Create your first extension and Manifest
Debugging Manifest V3 service workers	Manifest V3 troubleshooting and Background scripts
Shipping production extensions across browsers	Cross-browser compatibility and Workflows overview

Choose the right command

Goal	Command	Example
Scaffold a project	`create`	`npx extension@latest create my-extension --template=new-react`
Develop with watch mode	`dev`	`extension dev --browser=firefox`
Build production artifacts	`build`	`extension build --browser=chrome,firefox --zip`
Build and launch production output	`start`	`extension start --browser=edge`
Launch existing build output	`preview`	`extension preview --browser=chrome`

Start a new extension

Use the create command to scaffold a new project and --template to start from a stack-specific baseline.

npx extension@latest create <your-extension-name>

pnpx extension@latest create <your-extension-name>

yarn dlx extension@latest create <your-extension-name>

bunx extension@latest create <your-extension-name>

deno run -A npm:extension@latest create <your-extension-name>

For a list of all supported templates, browse the Templates page.

Use Extension.js with an existing extension

If you already have an extension, install the extension package and wire scripts once. This keeps local development, testing, and release builds consistent.

Step 1: install the `extension` package as a `devDependency`

npm install extension@latest --save-dev

pnpm add extension@latest --save-dev

yarn add extension@latest --dev

bun add --dev extension@latest

deno add npm:extension@latest

Step 2: link your npm scripts to the `extension` commands

package.json

{
  "scripts": {
    "build": "extension build",
    "dev": "extension dev",
    "start": "extension start"
  },
  "devDependencies": {
    "extension": "latest"
  }
}

Done. Your extension is ready to use.

Run npm run dev for daily iteration and watch mode.
Run npm run start for production build + immediate launch.
Run npm run build for store-ready production artifacts.

Best practices

Keep one command flow: Use create → dev → build as your default loop.
Target browsers explicitly: Validate with --browser=chrome,firefox before release.
Centralize defaults: Put shared command/browser settings in extension.config.js.

Next steps

Create your first extension

Guided walkthrough for your first build.

Templates

Browse starter templates for every stack.

Playwright E2E

Add quality gates to your workflow.

Telemetry and privacy

Review the privacy contract.

Compare frameworks

How Extension.js compares to other browser extension frameworks.

What is a browser extension?

⌘I

​Video walkthrough

​Choose your path

​Choose the right command

​Start a new extension

​Use Extension.js with an existing extension

​Step 1: install the extension package as a devDependency

​Step 2: link your npm scripts to the extension commands

​Best practices

​Next steps

Create your first extension

Templates

Playwright E2E

Telemetry and privacy

Compare frameworks

Video walkthrough

Choose your path

Choose the right command

Start a new extension

Use Extension.js with an existing extension

Step 1: install the `extension` package as a `devDependency`

Step 2: link your npm scripts to the `extension` commands

Best practices

Next steps