Responsive Breakpoint Tester

Test your website at common responsive breakpoints free online. Preview mobile, tablet, and desktop widths in a live resizable frame without switching devices.

375px

Loads your real site in an iframe -- some sites block embedding via X-Frame-Options.

How to Use This Tool

Enter your site's URLWhatever page you want to test

Click a breakpoint presetOr enter a custom width

Check your layout at each widthSee real rendering, not a mockup

Responsive Breakpoint Tester is a free online tool that works entirely in your browser — no signup, no data uploaded, no limits.

Real Rendering, Not a Simulated Mockup

This loads your actual live site inside an iframe set to the exact target width, so what you see responding (or breaking) is your real CSS and content at that real viewport size -- not an approximation or static screenshot.

Why These Specific Widths

375px, 768px, 1024px, and 1440px represent the de facto standard breakpoints most CSS frameworks and responsive designs target, covering typical mobile, tablet, laptop, and desktop viewport widths respectively.

A Note on Sites That Block Embedding

Some websites set headers (X-Frame-Options or Content-Security-Policy) specifically preventing embedding in an iframe for security reasons -- if your site does this, you'll need to temporarily adjust that setting to use this tool, or test using your browser's own responsive design mode instead.

Frequently Asked Questions

The common industry-standard breakpoints -- 375px (mobile), 768px (tablet), 1024px (small desktop/laptop), and 1440px (large desktop) -- covering the widths most CSS frameworks and media queries target.

Manually resizing a browser window to an exact pixel width is fiddly and imprecise. This snaps directly to the exact standard breakpoint widths with one click, making it faster to check how your layout responds at each specific target size.

It loads your site in a real iframe at the selected width, so you're seeing your actual live page rendering and responding to that viewport size, not a simulated approximation.

Yes, a custom width input lets you set any specific pixel value beyond the standard preset breakpoints, useful for checking an unusual width where your layout might break.

Media query breakpoints in your CSS might not align with where your actual content needs to reflow, or specific elements (long words, fixed-width components) might overflow regardless of breakpoint placement -- testing at these standard widths helps catch exactly that kind of gap.