ReSIzEr is a free Chrome extension developed by manutepowa. It falls under the category of Browsers and specifically the subcategory of Add-ons & Tools. This extension is designed to assist web developers in visualizing the responsive design of their websites on smartphones and tablets.

With ReSIzEr, developers can easily test the responsiveness of their websites by resizing the browser window to simulate different screen sizes. This allows them to see how their websites will appear on various devices and make necessary adjustments to ensure optimal user experience.

The extension is simple to install and use. Once installed, a toolbar icon appears in the Chrome browser. By clicking on the icon, developers can choose from a range of pre-defined screen sizes or customize their own. They can also toggle between landscape and portrait orientations.

ReSIzEr is a valuable tool for web developers who want to ensure their websites are responsive and user-friendly across different devices. It provides an easy and convenient way to test and fine-tune the responsiveness of websites, saving developers time and effort in the development process.