Viewport Resizer is a free Chrome add-on developed by Malte Wassermann. It falls under the category of Browsers and specifically the subcategory of Add-ons & Tools. This tool is designed to test the responsiveness of any website.

With Viewport Resizer, you can easily emulate various screen resolutions to see how a website adapts to different devices. After installing the extension, simply navigate to the page you want to test and choose from a range of screen resolutions to view the website in. This allows you to quickly assess how the website appears on different devices without the need for physical devices or extensive testing.

While Viewport Resizer provides a convenient way to test responsiveness, it is important to note that it should not replace real device simulation. Instead, it serves as a helpful tool for you, your team, and clients to test and review various aspects such as layout, text length, and transitions across different device types.

Overall, Viewport Resizer is a valuable tool for web developers and designers who need to ensure that their websites are responsive and visually appealing across different screen sizes.