ext0.dev

Open-source, all-in-one developer-tools browser extension for Chrome. Inspect CSS, pick colors, measure pages, preview responsive layouts, format JSON, and export elements from one toolbar.

Status

ext0 is currently a public beta. It is not available on the Chrome Web Store yet, but you can build it from source and load it locally as an unpacked Chrome extension.

Features

• CSS Inspector - inspect typography, layout, spacing, colors, and styles directly on the page.
• Color Picker - pick page colors and copy them in common formats.
• Page Ruler - measure distances and element sizes in the browser.
• Responsive Viewer - preview a page across common device sizes.
• JSON Formatter - auto-render JSON pages in a readable view.
• Export Element - copy selected HTML/CSS or open it in CodePen.

Install Locally

Requirements:

• Node.js 22+
• pnpm 9+

Build and load the Chrome extension:

pnpm install
pnpm --filter @ext0/extension build

Then open chrome://extensions, enable Developer mode, choose Load unpacked, and select:

apps/extension/.output/chrome-mv3

After pulling updates, run the build command again and reload the extension from chrome://extensions.

Privacy

ext0 has no accounts, payments, telemetry, or background reporting. Extension settings are stored locally in your browser. The only outbound request is user-triggered: the Export Element tool can post selected HTML/CSS to CodePen when you click Open in CodePen.

Read the full privacy policy, the extension permission notes, or the security policy.

Limitations

• ext0 is not yet published on the Chrome Web Store.
• Chrome blocks extensions on internal pages such as chrome:// URLs and the Chrome Web Store.
• Local installs are manual; rebuild and reload after updating the source.

Development

This monorepo contains two packages:

Package	Path	Description
@ext0/extension	apps/extension	Browser extension built with WXT, React, and Tailwind.
@ext0/web	apps/web	Marketing site at ext0.dev, built with Astro, React islands, and Tailwind.

Run the full workspace:

pnpm dev

Run a specific app:

pnpm --filter @ext0/extension dev
pnpm --filter @ext0/web dev

Common checks:

pnpm lint
pnpm typecheck
pnpm build

Contributing

Issues, ideas, and pull requests are welcome. Start with CONTRIBUTING.md, and please follow the Code of Conduct.

For help, visit support, open a GitHub issue, or start a GitHub discussion.

License

MIT (c) Wahyu Syahputra.