A viewport size bookmarklet.

Drag the button to your bookmarks → ViewportTester

ViewportTester displays the viewport width and height values straight from within CSS media queries.

Unfortunately there's no known way of detecting browsers' zoom levels. So when zoomed, it can be off by a fraction of a pixel. It's work in progress but wanted to get it into your hands ASAP.

Learn more about viewports, inconsistencies between browsers, and know how to detect size using JavaScript.

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