Until now, Google used content from a page's desktop version to index and rank websites, but switched links at the last moment to a site's mobile page if the user was searching from his mobile device. Moreover, it will still prefer mobile versions of sites over Google's fast-loading AMP pages in indexing.
This long-awaited rollout is part of Google's ongoing efforts to streamline the search and web experiences for mobile users, who are often whipping out their phone to look something up in a hurry in the heat of a moment and have limited time to spend sorting through results or dealing with pages that load slowly or don't work well on a mobile device.
Google noted that this new fashion of indexing will likely help the site "perform better" in mobile search results and directly won't affect how content is ranked.
Google insisted that it will only use one index in displaying search results, but will prioritize mobile-friendly sites over desktop versions.
France mourns 'hero' hostage-swap policeman after jihadi attack
Police killed the gunman after he had shot and stabbed Beltrame, who died of his injuries early on Saturday (March 24). He had been on an extremist watch list, but authorities believed he was not a threat.
Nonetheless, today's update is a landmark in Google Search's long history and evolution, marking the date when Google started giving mobile sites a big role in determining search engine rankings. After the shift, the mobile version of sites will be shown in Google's search results and cached pages.
But Google has also warned that having a mobile-friendly version of the original desktop site is not enough. And if a desktop site is more relevant to the search over mobile alternatives, it will be included in the results. Starting in July 2018, slow-loading content will be downranked.
Don't call it the mobile-first index, but rather call it mobile-first indexing. Site owners will see significantly increased crawl rate from the Smartphone Googlebot. I checked dozens and dozens of mobile-friendly popular sites and saw no signs that they moved over yet.
Things won't change a lot on Google Search Desktop, where content from the desktop versions of pages will continue to surface in search results as they did until now.