CSS Breakpoint Tester
Resize your browser window to see which CSS breakpoint is active. Supports Tailwind CSS, Bootstrap 5, and custom breakpoints.
100% client-side · no upload
Viewport width
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Active breakpoint
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Enter breakpoints as name:px pairs, one per line.
| Name | Min-width | CSS | Active |
|---|
How to use
- Resize your browser window and the indicator updates in real time.
- Select the framework preset (Tailwind, Bootstrap) or enter custom breakpoints.
- The active breakpoint is highlighted, showing which CSS rules are in effect.
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常見問題
- Is this tool free?
- Yes, completely free with no signup required.
- Does my data leave my device?
- No. Everything runs in your browser — nothing is sent to any server.
- Does it work on mobile?
- Yes. The tool is mobile-first and works on any modern browser including iOS Safari and Android Chrome.