Earlier this week, Google posted a reminder that they are starting to switch over to mobile-first indexing for their search results and rankings. Over a year ago, they had announced that they were experimenting with it, and now they’re ready to start rolling it out.

With the continuing increase of mobile users, Google is looking ways to ensure that these users are better able to find what they’re looking for. So, instead of indexing the desktop version of a site, Google will begin using what it finds in the mobile version as the primary source for its search results.

For sites that have identical content on both desktop and mobile versions of their site (or have a single site that uses responsive design), the ramifications of this impending change are negligible. Rather, the main issues would be for the sites that have different content on desktop and mobile versions of their site.

In those cases, it’s critical for site owners to ensure that the content on the mobile version contains everything they want to have indexed. This would include not only the copy of the site, but also any pertinent metadata (e.g. titles and descriptions) or structured data.

Although Google is starting to roll out this change, it’s being cautious in doing so. They’re taking their time, and for now, they’re turning on mobile-first indexing for individual sites when they see that the site is ready (see what Google thinks about your site on mobile). However, although they’re slowly rolling it out now, it will only be a matter of time when mobile indexing is used across the board.

How about performance?

In their recent announcement, Google focused primarily on the content of a site when viewed on mobile–the performance of a page on mobile wasn’t explicitly mentioned. But I think it’s safe to assume that performance will begin to impact the results of mobile-first indexing in the future.

Earlier this year, for instance, at SMX West, Google’s Gary Illyes noted that Google was working on a new page speed measurement for mobile, since the desktop speed wasn’t relevant. Knowing this, and knowing that Google has long used PageSpeed as a factor in its rankings, means it’s only a matter of time before mobile performance begins to have some impact on its search results.

Which means, it’s a great time to not only review the content of your site on mobile, but also its performance (here’s Google’s simple tool for checking mobile performance). Because with mobile becoming the primary source for Google’s search rankings, there’s all the more reason to optimize the mobile experience–both content and performance–for all your users.