What is Extension.js?#

Build browser extensions for Chrome, Edge, and Firefox with one modern workflow. Extension.js handles manifest compilation, browser-specific output, reload behavior, and packaging so you can focus on product features.

Use familiar web tooling like TypeScript, React, Vue, and Tailwind CSS. Keep direct access to native extension APIs.

Pick your path#

Choose the right command#

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>

For a list of all supported templates, check out 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

Step 2 - link your npm scripts to the extension commands#

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

That's it! You're all set.

• 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#

• Learn how to create your first extension.
• Explore built-in templates.
• Add quality gates with Playwright E2E.
• Strengthen reliability with Troubleshooting, Security checklist, and Performance playbook.