Testing your web site or application in different browsers and on different mobile devices is important, and there is no substitute for the real thing. However, not everyone has an iPhone, Google Nexus, Blackberry and the latest Samsung phone lying around.
So, being able to emulate a mobile or tablet device means you can test your site or application on these devices without actually owning them. While no emulator is guaranteed to be perfect, Chrome has a built-in emulator that will get you pretty close and supports a wide range of popular mobile and tablet devices.
All you need to do to start emulating a device is to open up the Chrome developer tools and click the icon of the mobile phone near the top left. This will reload the web page and provide you with the ability to select a mobile device from a dropdown. Once you select a device, be sure to reload the page so that the user agent is updated and Chrome properly emulates the device. To switch back to your normal desktop viewing experience, just click the mobile icon to toggle the emulator off and reload the page.