Responsive Viewport Tester
Preview any URL at common device viewport sizes. Test responsive breakpoints for mobile, tablet, and desktop.
URL to Test
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💡 Definition
Responsive Testing
- Responsive viewport testing previews websites at different screen sizes.
- Essential for ensuring layouts work across phones, tablets, and desktops.
📖 How to use
Step by Step
- Enter a URL and click Load
- Click preset device buttons to switch viewports
- Or enter custom width × height
- The page renders in the iframe below
🎯 Use cases
When to use
- Testing responsive CSS breakpoints
- QA for mobile-first designs
- Client presentations of responsive layouts
- Comparing layouts across device sizes
Frequently Asked Questions
Can I test localhost?▾
Due to browser security, localhost URLs may not load in the iframe. Deploy to a staging URL for testing.
Why might a site not load?▾
Some sites set X-Frame-Options headers that prevent iframe embedding. This is a security feature of those sites.