Responsive Design is the design of website that adjusts according to the screen and device and it displays according to it. The main feature of having responsive design is user doesn't have to zoom in the website and check the details. Instead, all the information will be given according to the device and thus easy for them, to go through the website. If any website has redirect mobile version of their website, that will not be displayed. Instead design that fit in screen size will be the result.
This tool helps to check the website design as it will look in particular device. Website name has to be entered in the textbox, screen resolution type or device has to selected then submit button to be clicked. Thus, it will display the website as it is designed according to screen. This tool helps the designer not have each screen resolution device as they can check in this particular tool itself.