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Responsive Breakpoint Previewer

Preview any URL at common responsive breakpoints (mobile, tablet, desktop) side by side or individually in an iframe.

About Responsive Breakpoint Previewer

The Responsive Breakpoint Previewer embeds any URL in iframes sized to common device breakpoints — allowing you to compare how a page looks at mobile (375px), tablet (768px), laptop (1280px), and desktop (1440px) widths simultaneously. Quickly test your own local development server, a staging URL, or any publicly accessible page without manually resizing your browser window or using DevTools device emulation. Each breakpoint frame is independently scrollable and shows the viewport width so you can correlate the appearance with your CSS media query breakpoints. Common CSS framework breakpoints (Tailwind, Bootstrap, Material) are provided as quick-load presets.

Why use Responsive Breakpoint Previewer

See multiple breakpoints simultaneously

See multiple breakpoints simultaneously without resizing your browser.

Includes presets for Tailwind

Includes presets for Tailwind, Bootstrap, and Material breakpoints.

Each frame is individually

Each frame is individually scrollable for full page inspection.

Works with localhost and

Works with localhost and any publicly accessible URL.

See multiple breakpoints simultaneously

See multiple breakpoints simultaneously without resizing your browser or opening DevTools.

Includes presets for Tailwind

Includes presets for Tailwind, Bootstrap, and Material breakpoints — match your framework's tokens.

How to use Responsive Breakpoint Previewer

  1. Enter the URL of the page you want to preview in the address bar.
  2. Click Preview to load it in the breakpoint frames.
  3. Use preset breakpoints or enter custom pixel widths.
  4. Click any frame to expand it to full view for detailed inspection.
  5. Use preset breakpoints (Tailwind, Bootstrap, Material) or enter custom pixel widths.
  6. Toggle between 'all visible at once' grid and 'one at a time' carousel modes.
  7. Reload all frames simultaneously when you push code changes to localhost.

When to use Responsive Breakpoint Previewer

  • Quickly checking a responsive design at multiple breakpoints during development.
  • Comparing mobile and desktop layouts side by side for a client review.
  • Verifying breakpoint changes after editing CSS media queries.
  • Testing a staging URL at device-specific widths before launch.
  • Comparing mobile and desktop layouts side by side for a client review or stakeholder demo.
  • Reviewing a competitor's responsive design quickly across viewports.

Examples

Tailwind preset comparison

Input: URL: https://example.com — preset: Tailwind

Output: Frames at 640px (sm), 768px (md), 1024px (lg), 1280px (xl), 1536px (2xl) loaded simultaneously.

Localhost dev server

Input: URL: http://localhost:3000 — widths: 375, 768, 1280

Output: Three frames preview your local Next.js or Vite app at iPhone, iPad, and desktop widths.

Custom edge cases

Input: URL: staging.example.com — widths: 320, 412, 1920

Output: Tests narrow Android (320), modern Pixel (412), and full HD (1920) — covers extremes traffic actually sees.

Blocked iframe site

Input: URL: https://accounts.google.com

Output: Frames render blank — Google sets frame-ancestors 'self', so external preview is impossible. Use DevTools instead.

Tips

  • When testing localhost, use 0.0.0.0 instead of localhost if you need to load the URL from another device — but the iframes load the same browser context, so localhost works fine here.
  • Add 320px (smallest common mobile) and 1920px (full HD) as custom widths to bracket your real-world traffic.
  • Some sites set frame-ancestors CSP headers and refuse to load in iframes — major sites like Google, Facebook, and bank logins are blocked. Test those in DevTools instead.
  • Use the 'reload all' button after deploying so every frame refreshes against the new code in one click.
  • If a frame shows scrollbars at all widths, your page has horizontal overflow — investigate min-width or fixed-width content.
  • Test landscape phones (812px width) too — many designs only check portrait widths and break in landscape.

Frequently Asked Questions

Can I preview localhost URLs?▾
Yes. As long as your browser can access the URL, the previewer can load it. localhost and 127.0.0.1 addresses work when running from the same machine.
Why might some pages not load in the frames?▾
Pages with X-Frame-Options: DENY or Content-Security-Policy: frame-ancestors 'none' headers refuse to be embedded in iframes. Many major websites use these headers.
Does it simulate touch events?▾
No. The frames are iframes at the specified width — touch event simulation and media queries responding to pointer type require DevTools device emulation.
What breakpoints does Tailwind use?▾
Tailwind v3 default breakpoints: sm=640px, md=768px, lg=1024px, xl=1280px, 2xl=1536px.
Can I add a custom breakpoint?▾
Yes. You can enter any custom pixel width in addition to the preset breakpoints.
Does this account for device pixel ratio?▾
No. Iframes render at CSS pixel widths regardless of your monitor's DPR. For DPR-sensitive testing (retina image swaps), use DevTools device emulation.

Explore the category

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Aspect Ratios in Web Design: A Complete Guide Aspect ratios determine how images and videos fill their containers. Getting them wrong causes layout shift and distorted media. CSS now has Apr 2026 · 7 min

Glossary

Breakpoint
A viewport width threshold at which a CSS layout changes — typically expressed as min-width or max-width media queries.
Media query
CSS @media rule that applies styles only when conditions are met (viewport width, orientation, prefers-color-scheme, etc.).
Mobile-first design
Authoring CSS for the smallest viewport first, then layering larger-breakpoint overrides via min-width media queries.
Viewport
The visible area of the browser window (or iframe). Measured in CSS pixels, not device pixels — separate from physical screen resolution.
Device pixel ratio (DPR)
Ratio of physical pixels to CSS pixels. Retina screens have DPR 2 or 3 — important for image sourcing but transparent for layout.
Tailwind breakpoints
Default Tailwind v3 breakpoints: sm=640px, md=768px, lg=1024px, xl=1280px, 2xl=1536px. Customizable in tailwind.config.js.
X-Frame-Options / frame-ancestors
HTTP headers that prevent a page from being embedded in iframes. Many major sites set these for clickjacking protection — those URLs cannot be previewed.
Container query
Modern CSS feature that styles based on the size of a parent container rather than the viewport. Complements but doesn't replace media queries.