Creating an intuitive and powerful experience is a tough problem. In order to help web designers get a balance, Google launched a new sizer testing tool. It can test material design across platforms and see the breakpoint position, but its purpose is not to show you the best side of the web page, but to let you feel what the website looks like on the mobile platform in real time. You can test any web address through the sizer, such as the TNW home page shown in the figure below.
After you enter a URL, you can switch between the desktop / mobile experience. The Sizer is very interactive and closely mimics' real 'performance.
The sizer fully follows the material design language. The address bar also provides some default URLs for your comparison experience, such as test breakpoints, responsive components, surface behavior, and UI patterns.
Although sizer can't help you design a web page directly, it is a very convenient and practical performance testing tool.