Google announces that after a year and a half of careful experimentation and testing, we’ve started migrating sites that follow the best practices for mobile-first indexing. To recap, our crawling, indexing, and ranking systems have typically used the desktop version of a page's content, which may cause issues for mobile searchers when that version is vastly different from the mobile version. Mobile-first indexing means that we'll use the mobile version of the page for indexing and ranking, to better help our – primarily mobile – users find what they're looking for. Best practices for mobile-first indexing - https://developers.google.com/search/mobile-sites/mobile-first-indexing Google crawlers - https://support.google.com/webmasters/answer/1061943 Source - https://webmasters.googleblog.com/2018/03/rolling-out-mobile-first-indexing.html