At an industry event this week in New York City, Google’s Gary Illyes spoke about one of the search giant’s latest endeavors: mobile-first indexing. Illyes said this project has begun to roll out, with an undisclosed number of websites already affected. The timeline for a complete roll-out also remains undisclosed.
All of this “undisclosed” information makes the development sound more ominous than it is. We apologize for that. Information is scarce at this early stage, but don’t panic. Mobile-first indexing isn’t scary as long as you have a mobile-optimized website.
You see, the mobile-first index is just a different way for Google to create and rank its search listings. While Google has historically created this index based on desktop versions of websites, it will now be doing so based on mobile versions.
When Google first announced the mobile-first index project nearly a year ago, in November 2016, Barry Schwartz of Search Engine Land explained it like this:

As more and more searches happen on mobile, Google wants its index and results to represent the majority of their users — who are mobile searchers.
Google has started to use the mobile version of the web as their primary search engine index. A search engine index is a collection of pages/documents that the search engine has discovered, primarily through crawling the web through links. Google has crawled the web from a desktop browser point of view, and now Google is changing that to crawl the web from a mobile browser view.

The key here is mobile-optimized websites, not just mobile websites. In other words, any old mobile version of your website won’t do. Your mobile site must be an identical match with your desktop site. All content and links should be the same on each version. If your mobile site has less content or fewer pages, it won’t rank the same. Therefore, websites with a responsive design (meaning they adapt to any screen size without losing readability or usability) will be the most successful with this new index.
Long story short: A mobile-optimized website just became your star player. You can’t win without it.
Again, Google (in typical fashion) isn’t giving us very much information about the development beyond what we’ve shared here. However, according to Illyes, Google does plan on making an official announcement, including a thorough explanation and roll-out timeline, on its blog some time in the near future. Stay tuned, we guess?
In the meantime, go ahead and check out what we know so far over on Search Engine Land!