Screen Size Simulator

The page loads in a window of the selected size. Our server never downloads it: only one request leaves the server, to read the response headers, so the site owner sees a normal visit.

The headers show in advance whether the site allows being displayed inside other pages. When a site blocks this, the tool says so directly and names the reason, instead of leaving an empty window.

Sizes in the list are CSS pixels, the width that media queries see. Phones have two to three times more physical dots, but the layout never sees them: an iPhone 15 is 393 pixels to a stylesheet, not 1179. Testing by physical dots would show the desktop layout instead of the mobile one.

A screen larger than the window is scaled down as a whole, with the scale factor labeled next to it; clicking the label shows the page at 1:1. Rotation switches the portrait window to a wide one, and a custom size is set in fields from 200 to 4000 pixels.

This is a layout check by window width, not a phone emulation: touch events, screen density, and a mobile User-Agent are not faked. When the behavior of a specific device matters, you need the phone itself or your browser's device mode.