Responsinator

Responsinator is the fastest tool for seeing how a website behaves on different mobile devices: paste the URL and immediately get a side-by-side view on iPhone, Android and iPad, both portrait and landscape.

Responsinator is a free web tool for testing a site's responsive design. It works instantly: enter the URL of the site you want to check and Responsinator loads and displays the page simultaneously in a series of screen sizes simulating the most common mobile devices — iPhone portrait and landscape, Android phone, iPad, Android tablet. All previews are shown on a single scrollable page, so you can compare at a glance how the site adapts to different resolutions. It's a simple, niche tool widely used by web designers and front-end developers during the testing phase of responsive design. It's not a substitute for testing on real devices or browser developer tools — it has limitations on complex JavaScript and advanced interactions — but it's useful for a quick visual check before moving to more thorough testing.

For web designers, front-end developers and anyone wanting to quickly check how a site looks on different mobile devices without opening a different browser or using developer tools.

Responsinator is completely free, with no registration and no paid plans. It's a minimalist tool that does one thing — displaying a URL at different screen sizes — with no additional features or premium options.