Preview how websites look across different device screen sizes
Enter a website URL and click Load to preview it at the selected device size.
Many websites use X-Frame-Options or Content-Security-Policy headers to block iframe embedding for security. This prevents clickjacking attacks.
Works best with local dev servers (localhost), sites that allow iframe embedding, or your own websites under development.
Viewport size is accurate, but actual device rendering engines, pixel density, and touch interactions cannot be simulated. Final testing should be done on real devices.
Useful for viewing large viewports (desktop, laptop) on smaller screens, or zooming in on details of small viewports.
Responsive Web Design is an approach that provides optimized layouts for various screen sizes from a single HTML source. CSS media queries (@media) are used to dynamically change layouts, font sizes, and spacing at specific viewport widths. Tailwind CSS prefixes like sm:, md:, lg: and Bootstrap's grid system also operate on the same responsive principles. Properly implemented responsive design delivers optimal experiences for mobile, tablet, and desktop users alike.
The most commonly used mobile viewports today are 390px (iPhone 14) and 360–412px (mainstream Android), while tablets range from 768–1024px and desktops from 1280–1920px. However, a device's physical resolution and CSS pixels (logical pixels) are different. For example, the iPhone 14 has a physical resolution of 2532×1170 but a CSS pixel viewport of 390×844, because the device pixel ratio (DPR) is 3x. Media queries operate based on CSS pixels.
A viewport simulator lets you quickly check layouts at various screen sizes without physical devices. Catching layout errors early in development significantly reduces the cost of fixes. It is especially useful for catching common mobile issues like text clipping, overlapping buttons, and broken image ratios before they reach production. However, for final quality verification, direct testing on actual devices is recommended.