shrink.mathlab.cc — Preview any website as a mobile device — directly in your browser, with zero setup.

• No analytics, no tracking — nothing leaves your browser
• No ads, no paywalls, no accounts
• Open source (MIT)
• Works on Chrome and Firefox

• 24+ devices — iPhone, Samsung Galaxy, Google Pixel, iPad, and more
• Browser mode switching — Chrome, Firefox, Safari user agents
• Portrait & landscape rotation
• Light / Dark / Auto color scheme emulation (prefers-color-scheme via CDP)
• Network throttling presets (Slow 3G / Slow 4G / Fast 4G)
• Screenshot — capture the simulated viewport as a PNG
• Remembers your last device and settings
• Sidebar device picker with instant search

This is a pnpm workspaces monorepo:

apps/
  extension/      # the browser extension (WXT, MV3)
  landing-page/   # marketing site (TanStack Start + Tailwind v4 + Nitro)

Prerequisites: Node.js 22+, pnpm 9+

pnpm install

pnpm dev:ext             # Chrome (default)
pnpm dev:ext:firefox     # Firefox
pnpm build:ext           # production build → apps/extension/.output/chrome-mv3
pnpm build:ext:firefox   # production build → apps/extension/.output/firefox-mv2
pnpm test                # Playwright tests

Load the extension:

• Chrome: go to chrome://extensions, enable Developer Mode, click "Load unpacked", select apps/extension/.output/chrome-mv3
• Firefox: go to about:debugging, click "This Firefox", click "Load Temporary Add-on", select any file inside apps/extension/.output/firefox-mv2

pnpm dev:lp        # http://localhost:3000
pnpm build:lp      # production build → apps/landing-page/.output (Nitro node-server)

Run the production build locally:

node apps/landing-page/.output/server/index.mjs

The landing page ships with a multi-stage Dockerfile (Node 24 alpine, Nitro node-server preset).

• Build context: repository root
• Dockerfile: apps/landing-page/Dockerfile
• Exposed port: 3000

Extension:

• WXT — extension build framework
• Chrome DevTools Protocol (CDP) — device metrics, UA, touch, color scheme emulation, network throttling
• Firefox Declarative Net Request (DNR) — header modification
• Shadow DOM — isolated extension UI with no style conflicts
• TypeScript, Biome

Landing page:

• TanStack Start — full-stack React framework
• Nitro — node-server preset
• Tailwind v4
• Motion (Framer Motion successor)

MIT — see LICENSE