Question 1

Why does the preview show an error or blank page?

Accepted Answer

Many websites block iframe embedding via X-Frame-Options or Content-Security-Policy headers for security. This prevents them from being previewed in tools like this. Local files (file://) and many major sites (Google, GitHub) have this restriction. Use browser DevTools device mode as an alternative for those sites.

Question 2

How accurate is this compared to real devices?

Accepted Answer

This tool simulates viewport dimensions, not actual devices. It doesn't replicate device-specific features like touch gestures, device pixel ratio, iOS Safari quirks, or Android Chrome behavior. For comprehensive testing, use real devices or browser DevTools device emulation which includes more device characteristics.

Question 3

What's the difference between portrait and landscape?

Accepted Answer

Portrait orientation is taller than wide (like holding a phone upright). Landscape is wider than tall (like turning a phone sideways). Desktop monitors are essentially always landscape. Test both orientations as layouts may break or behave differently when dimensions swap.

Question 4

Can I test my local development site?

Accepted Answer

If your local server allows iframe access (no X-Frame-Options restrictions), you can use localhost URLs. However, many local development configurations block embedding. Consider using ngrok or similar tunneling services with appropriate headers, or use browser DevTools instead.

Responsive Design Tester

What is Responsive Design Testing?

How to Use This Responsive Design Tester

Common Viewport Breakpoints

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