A responsive website is a single website that dynamically resizes its content and images for a variety of different screen sizes in order to serve all users irrespective of the device they use to access the site.

Google has provided a tool to test your website for mobile responsiveness. You can test it in Google mobile-friendly test site. This website itself is a mobile friendly site. You can click here to see the mobile friendly test result page for this website. This website allows to test how certain web page will look like on various screen sizes. So it is recommended that this website is accessed on the big screen sizes(Laptops and desktops) for the testing.

Mobile responsiveness will affect your website’s search engine rankings. Mobile responsive sites will be valued higher than sites which aren’t responsive. Google will give a completely different set of search results for people on mobile devices. If your website is not mobile responsive, then it may not be included in the mobile results. Because half of the internet’s traffic is mobile, if your site is not on the mobile index you could potentially lose half of the traffic you receive from Google.

With a responsive website, you don’t have to have separate websites for desktops and mobile phones, so you also end up saving money.

You will lose site rankings and traffic. Considering the mobile usage breakthrough, Google announced that a completely separate index (a separate set of search engine results) will be implemented for mobile users. This means mobile users receive different results than desktop users. Websites which are mobile responsive will receive indexing preference in Google’s mobile search results, non-responsive won’t. With over half of internet usage coming from mobile devices, responsive design is a must-have for websites going forward.

All major latest versions of browsers such as Chrome, Firefox, Safari, etc., support responsive websites.

Yes, you can test your website for mobile responsiveness. You can use this website to test how your website will look like on various devices. If you can't find the device you want to test on the list of devices in the dropdown list, you can send a request to add it in the list by submitting the details in the contact section.

No, it does not support local html files. Your web pages should be hosted on the server to perform this mobile friendly testing.

There is one reason for this. The URL you entered might have hotlink protection enabled. Hotlink protection feature prevents other websites from accessing the files hosted on the particular website. This feature is used to protect the bandwidth by disallowing other domains from linking to content (images/videos/files) of the desired website. This feature is also know as Cross Origin Resource Sharing(CORS) policy. For more details you can read this wiki page.

If the web URL you try to test is your own domain or if you have the access to change the hotlink protection settings, you can add https://mobilefriendlytester.com site in your hotlink protect list to allow direct accessing. Once your testing is performed, you can remove it from the hotlink protection list.

You can test both HTTP and HTTPS URLs if cross-origin resource sharing is enabled for those URLs.

Developing a responsive website is easy with Bootstrap framework. Bootstrap is the most popular HTML, CSS, and JavaScript framework for developing responsive, mobile-first web sites. Bootstrap is completely free to download and use. You can check https://www.w3schools.com site to learn bootstrap.