Viewport resizers are so handy when it comes to testing responsive layouts with no pain.

ish is an open source and simple app which is built with HTML-JS (although the source comes with a PHP file, check this to make it PHP-free).

ish Viewport Resizer

It loads any given URL inside an iframe where the iframe can be resized with the help of predefined or custom widths so that it becomes possible to see how the layout reacts.

There is also a fun “Disco” mode that auto-changes the width regularly and we only need to watch to see if any issues exist with the layout.

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