Preview Your Responsive Design on Any Device Preview websites at common device breakpoints with a built-in iframe viewer.

🎨

Responsive Design Tester

Preview websites at common device breakpoints with a built-in iframe viewer.

Enter a URL

Paste the website URL you want to test for responsiveness.

Select a device

Choose from preset device sizes or enter custom dimensions.

Preview and test

View the website at the selected size with adjustable zoom.

Loading tool...

What Is Responsive Design Tester?

The Responsive Design Tester lets you preview websites at common device breakpoints using a scalable iframe viewer. Responsive design ensures websites look and function well across all screen sizes, and testing is essential. This tool provides preset device sizes for popular devices: iPhone SE, iPhone 14, iPhone 14 Pro Max, iPad Mini, iPad Pro, laptop, and desktop. You can also set custom dimensions for specific testing needs. The zoom control scales the preview to fit your screen while maintaining accurate dimensions. The tool also generates a corresponding media query for the selected breakpoint, helping you write targeted CSS for each device size.

Why Use Responsive Design Tester?

Preset sizes for popular iPhone, iPad, and desktop devices
Custom dimension support for specific testing needs
Adjustable zoom for comfortable viewing of any device size
Auto-generated media query for each breakpoint

Common Use Cases

Mobile Testing

Preview websites on iPhone and Android screen sizes without physical devices.

Breakpoint Debugging

Identify where layouts break by testing at specific pixel widths.

Client Presentations

Demonstrate responsive behavior across devices in client reviews.

QA Testing

Verify layout and content at standard breakpoints during quality assurance.

Technical Guide

The responsive tester uses a CSS-scaled iframe to simulate device viewports. The iframe is set to the actual device dimensions (e.g., 390x844 for iPhone 14), then CSS transform: scale() is applied to fit it within the visible area. The transform-origin: top left ensures proper scaling behavior. This approach provides an accurate representation of how the website renders at the target resolution. Note that this is a viewport simulation—it does not replicate device-specific rendering engines, touch behavior, or device pixel ratios. For accurate device testing, use browser developer tools or real devices. The generated media query uses max-width by default, following the mobile-first approach where you can then add min-width queries for larger screens.

Tips & Best Practices

1
Test at multiple breakpoints, not just preset device sizes
2
Pay attention to content between breakpoints, not just at them
3
Check both portrait and landscape orientations for mobile devices
4
Use the generated media queries as starting points for your CSS

Related Tools

CSS Flexbox Playground

Visual CSS Flexbox explorer with interactive controls for all flex container properties.

🎨 CSS & Design

CSS Grid Playground

Visual CSS Grid builder with interactive controls for template columns, rows, and gaps.

🎨 CSS & Design

Media Query Generator

Generate CSS media queries with feature conditions and preset breakpoints.

🎨 CSS & Design

Tailwind CSS Playground

Apply Tailwind CSS utility classes to elements with live preview and HTML output.

🎨 CSS & Design

Frequently Asked Questions

Q Is this the same as testing on a real device?

No, this simulates viewport size but does not replicate device-specific rendering, touch behavior, or pixel density.

Q Why does my site look different than on a real phone?

Real devices have different pixel densities, rendering engines, and touch-specific behaviors not replicated by viewport simulation.

Q Can I test interactive features?

Yes, the iframe loads the full website so you can interact with it, though some features may be restricted by cross-origin policies.

Q Does this tool simulate retina or HiDPI displays?

This tool tests viewport width, not pixel density. Use device pixel ratio media queries for retina-specific styles.

Q Can I test local development servers?

Only if the URL is accessible from the internet. Localhost URLs will not work in the iframe.

About This Tool

Responsive Design Tester is a free online tool by FreeToolkit.ai. All processing happens directly in your browser — your data never leaves your device. No registration or installation required.