Viewport Lab

Test responsive layouts without resizing your browser window. Viewport Lab lets you resize the real viewport of your current tab while keeping the page open and its state intact. Check different layouts directly on the website you are using, with your forms, navigation and interactions still available. Drag to resize. Enter dimensions for precision. • Drag the right edge to adjust width. • Drag the bottom edge to adjust height. • Drag the corner to change both. • Enter exact pixel dimensions in the compact control strip. • Use keyboard arrows for fine adjustments, or hold Shift for 10-pixel steps. Media queries, viewport units and responsive layouts react to the selected dimensions. Viewport Lab changes the actual page viewport without wrapping the site in an iframe or reloading it during activation and resizing. Your chosen dimensions stay active as you navigate within the same tab. Reset to the original size or close Viewport Lab whenever you are finished. Built for developers and designers. Check breakpoints, inspect layout changes and test real interactions on live websites or local development projects. Private and open source. No account, telemetry or external services. Page data is not transmitted, and active viewport settings are stored only in your browser session. Viewport Lab uses Chrome’s debugger API, so Chrome displays a debugging banner while it is active. It tests desktop responsive layouts; it does not simulate mobile hardware or touch input.