Preview any website or page at different viewport sizes. Best free online responsive design tester – no sign-up required, 100% free.
Preview any public website at different screen sizes. Works only for sites that allow embedding via iframe.
Create CSS gradients with preview.
Convert between color formats.
Find opposite colors.
Generate box-shadow values.
Convert pixel units.
Random hex colors.
Responsive design requires testing websites at various screen sizes to ensure they work correctly on all devices. The Responsive Design Tester lets you preview any webpage at common viewport sizes including mobile, tablet, laptop, and desktop resolutions.
You can enter any URL and view it within an iframe at your chosen dimensions. The tool includes preset buttons for popular devices and custom width/height inputs.
Testing across multiple viewport sizes is crucial because over half of web traffic now comes from mobile devices. A site that looks perfect on a desktop monitor may have overlapping elements, tiny text, or broken layouts on smaller screens. This tool simulates real device dimensions so you can identify and fix responsive issues during development rather than after deployment. The preset device buttons cover the most common screen sizes, saving time compared to manually entering dimensions for each test case.
Device presets: iPhone 14 (390×844), iPad Pro 11" (834×1194), Desktop FHD (1920×1080)
Custom: Enter any width and height to test specific breakpoints.
Yes, as long as the local server is running, you can test localhost URLs in the viewport tester.
Some websites block loading in iframes via X-Frame-Options headers for security reasons.
Yes, each preset uses the actual screen dimensions of popular devices in CSS pixels, providing accurate testing conditions.
Yes, Responsive Design Tester is completely free to use with no hidden costs, subscription fees, or premium tiers. All features are available without any payment required.
No. Everything runs locally in your browser using client-side processing. Your text and files never leave your device and are not stored on any server.
Yes, the tool is fully responsive and works on all devices including smartphones, tablets, and desktop computers. The interface adapts to any screen size.
No account or sign-up is required. You can use the tool immediately without any registration, login, or personal information.
There is no hard limit for typical use cases. Very large inputs may experience slower performance, but standard usage is processed instantly.
The tool works on all modern browsers including Chrome, Firefox, Safari, Edge, and Opera. It uses standard web technologies for broad compatibility.
Once the page is loaded, the tool runs entirely in your browser. You can continue using it even with intermittent internet connectivity since all processing is client-side.
Yes. Since all processing happens locally in your browser without any data transmission to servers, it is safe to use with sensitive or confidential information.
The tool provides real-time processing for standard inputs. Most operations complete in milliseconds because all computation happens directly in your browser without network latency.
