Responsive Window Resizer

Responsive Window Resizer opens a page in a separate test window with the viewport size you choose, such as 390 × 844 or 1366 × 768. It measures the browser frame on a blank page first, resizes the window so the visible page area matches your size as closely as the browser allows, reports the measured size, and then loads your URL.

1. 1.Enter the page URL, or keep this page.
2. 2.Pick a preset or type a width and height between 200 and 3840 by 200 and 2160 pixels.
3. 3.Select Open test window and allow pop-ups if the browser asks.
4. 4.Check the result: requested and measured viewport sizes.
5. 5.Save sizes you use often; they stay in this browser.

• •Ten common phone, tablet and laptop presets, plus saved sizes of your own.
• •Width and height swap for portrait and landscape checks.
• •The measured viewport is reported honestly, including pop-up blocking, screen limits and browsers that ignore resizing.
• •Live viewport, window, screen and device pixel ratio of this tab.
• •Nothing is uploaded; the URL is only opened in the window you launch.

Browsers only let a page resize pop-up windows it opened itself, never your current tab, and mobile browsers usually ignore resizing. This is a viewport-size launcher, not device emulation: device pixel ratio, touch, mobile browser toolbars, user agent, CPU and network speed and platform fonts are not emulated. Use browser DevTools device mode for that. After a page from another site loads, the tool can no longer read or resize the window.