What Is a Responsive Website Checker?
A responsive website checker is an online tool that lets you preview how a website renders across different screen sizes and device types — without needing a physical phone, tablet, or resizing your browser manually. It simulates the exact viewport dimensions that real devices use, giving you an accurate mobile-friendly test result in seconds.
Our tool uses sandboxed iFrames to load your target URL inside a precise viewport — 375px for mobile (iPhone), 768px for tablet (iPad), and 1280px for desktop — directly inside your browser. This means the rendering is real, not a screenshot simulation.
Whether you are a web developer debugging a CSS media query, a designer checking pixel-perfect layouts, or a business owner verifying your landing page looks great on all devices — this is the fastest way to do it for free.
Live viewport rendering — no screenshots