Screen Flex by Elesari Labs

Screen Flex is a fast, beautifully designed browser extension that lets you resize your window, preview any webpage inside a realistic device frame, and capture polished screenshots of the result. Whether you're building responsive layouts, auditing a landing page, filing design QA bugs, or just curious how a site looks on mobile, Screen Flex gives you an instant answer.

Resize the browser to any size, instantly. Pick from common presets (Mobile S, Tablet, Laptop L, Desktop 4K, and more), or type in custom width and height values. Choose between Window mode (resize the whole browser window) or Viewport mode (resize so the page's visible area matches an exact size, with the browser chrome automatically accounted for).

Preview pages on real device frames. View any page inside a pixel-accurate iPhone 17 Pro Max, iPad Pro 13", or MacBook Pro 16". The simulator renders the actual device bezel with the iOS 26 "Liquid Glass" Safari chrome or the macOS 26 "Tahoe" menu bar on top. Status bars, clocks, and icons update live. The URL bar in your browser stays unchanged so refreshing and navigating still work normally.

Live Viewport Tester. Open a dedicated page that shows your current window size in giant numbers and updates in real time as you drag. Save any size straight to your presets list with one click.

Screenshots and captures. Take a clean PNG of the device view. The screenshot is cropped precisely to the device screen area so the output is ready to drop into design specs, bug reports, or marketing assets.

Favorites and right-click access. Star the presets you use most. Favorites show up in the popup and also in the right-click context menu under "Screen Flex > Presets" so you can resize without ever opening the popup.

Smart defaults, no clutter. No accounts, no sign-in, no ads, no tracking. Everything is stored locally in your browser profile. Your presets sync across your signed-in browsers through the built-in storage API.