Viewport Lab

Viewport Lab helps developers and designers spot responsive-layout problems without repeatedly resizing a browser window. Click the toolbar icon to open the current page in a focused mobile viewport. Switch to the shared canvas to compare six common widths at once, or enter another HTTP or HTTPS address. Highlights: • focused single view and six-viewport comparison grid; • eight presets from 320×568 through 430×932 CSS pixels; • shared zoom, wheel or trackpad panning, and fit-to-canvas control; • reload and direct open-page actions; • no analytics, advertising, remote code, or broad website permissions. Viewport Lab compares responsive CSS layout. It does not emulate device hardware, DPR, touch input, network conditions, browser engine, or user agent. Some pages block iframe previews through their own security policy; use Open page when that happens.