Viewport Lab

A Chrome extension that displays the current page at the screen sizes you need: one large phone preview or six sizes side by side, without repeatedly resizing windows or DevTools.

Version: 1.1; store version is currently 1.0
Browsers: Chrome, Chromium, Brave, Vivaldi
Access: activeTab only
License: MIT

Add to Chrome Source code

The same page at six phone sizes, side by side on one canvas — Phone grid: 390, 375, 414, 393, 360 and 384 CSS pixels.

Why

Responsive layouts break at specific widths: a heading wraps in the wrong place, a card overflows at 360 pixels, or a tablet falls between two breakpoints. Viewport Lab shows those widths together so you can see the differences at a glance.

Features

Single screen — an exact CSS viewport fitted to the window.
Phone grid — six popular sizes on one canvas.
Tablet → desktop — 430, 600, 768, 1024 and 1280 pixels, covering large phones through small desktops.
Rotation — switch the same viewport to landscape with one button.
Custom dimensions — any width and height from 240 to 3840 pixels.
Canvas — shared zoom, panning and a Fit button.
Saved settings — mode, dimensions and orientation survive reopening.

Examples

One page at a 390 by 844 pixel viewport — Single screen: 390 × 844, scaled to the window.

The same phone rotated to a landscape viewport of 844 by 390 pixels — Rotation: the same phone in landscape.

Six viewport sizes spanning a large phone to a small desktop — Tablet → desktop range: 430 to 1280 pixels.

Keyboard shortcuts

Alt + Shift + V   open the current page in Viewport Lab
1                 single screen
2                 grid
O                 rotate
F                 fit the grid to the window
R                 reload previews

Shortcuts use physical key positions, so they also work with a Russian keyboard layout.

Installation

Open the Chrome Web Store page and click Add to Chrome.
Open a website and click the Viewport Lab icon or press Alt + Shift + V.
You can also enter another URL, including localhost for local development.

Works in Chrome, Chromium, Brave and Vivaldi.

Privacy

The extension requests only activeTab: it reads the current tab’s URL after your click, and that URL stays on your computer. There is no analytics, advertising, remote code or access to all websites. Privacy policy.

Limitations

Compares CSS viewport sizes, without emulating hardware, DPR, touch input, network conditions or user agent.
Some websites refuse to load in frames. Use Open site for those pages.

Status

Version 1.0 is published in the Chrome Web Store. Version 1.1 adds rotation, custom dimensions, shortcuts and saved settings; it has been under store review since October 31 and will be released after approval. Source code is open under MIT: github.com/vixkosla/browser-extensions.