Google today announced it has started rolling out mobile-first indexing for its search results. The company is migrating sites that follow best practices for mobile-first indexing to use the the mobile version of the page instead of the desktop version.

Google first started experimenting with a mobile-first index in November 2016. Until then, its search engine’s crawling, indexing, and ranking systems exclusively used the desktop version of a page’s content.

Google has found that relying only on the desktop version can cause issues for mobile searchers because desktop content sometimes differs from mobile content. Given that the majority of users are now on mobile, mobile-first indexing aims to use the mobile version of the page to make sure search results line up with the content that you see when you click through.

But this is going to be a gradual transition. Google says ranking isn’t part of the equation, yet:

Mobile-first indexing is about how we gather content, not about how content is ranked. Content gathered by mobile-first indexing has no ranking advantage over mobile content that’s not yet gathered this way or desktop content. Moreover, if you only have desktop content, you will continue to be represented in our index.

It’s also worth noting that Google is not implementing two search indices, as it once proposed. There is no “mobile-first index” separate from the main index that has existed since the search engine first started crawling pages. Google is simply shifting from indexing the desktop versions to the mobile versions of content.

Site administrators and developers take note

Sites that Google migrates to mobile-first indexing will be notified via the Google Search Console. Site owners will see a “significantly increased crawl rate” from the Smartphone Googlebot and Google will start showing the mobile version of pages in search results and cached pages.

Google released an updated version of the Search Console at the start of the year. Performance played a big role in the update, and now mobile is also getting some love.

The bigger picture here is that Google wants to “encourage webmasters to make their content mobile-friendly.” Even if the mobile-first indexing does not affect ranking right now, Google still evaluates all content in its index to determine how mobile-friendly it is.

Google already ranks “mobile-friendly” sites higher and negatively ranks mobile interstitials. In July, Google’s search engine will start ranking faster mobile pages higher as well.

If you are a site administrator or web developer, check out Google’s documentation for more information.