How Does Mobile-First Indexing Work, and How Does It Impact SEO?

We’ve been hearing a lot about mobile-first indexing lately, as the latest development in Google’s ever-continuing efforts to make the web more mobile-friendly and reflect user behavior trends. In this post I’ll go over the basics of what “mobile-first indexing” means, and what you may need to do about it

Mobile-first indexing is exactly what it sounds like.  It just means that the mobile version of your website becomes the starting point for what Google includes in their index, and the baseline for how they determine rankings. If you monitor crawlbot traffic to your site, you may see an increase in traffic from Smartphone Googlebot, and the cached versions of pages will usually be the mobile version of the page.

It’s called “mobile-first” because it’s not a mobile-only index: for instance, if a site doesn’t have a mobile-friendly version, the desktop site can still be included in the index. But the lack of a mobile-friendly experience could impact negatively on the rankings of that site, and a site with a better mobile experience would potentially receive a rankings boost even for searchers on a desktop.

You may also want to think of the phrase “mobile-first” as a reference to the fact that the mobile version will be considered the primary version of your website. So if your mobile and desktop versions are equivalent — for instance if you’ve optimized your content for mobile, and/or if you use responsive design — this change should (in theory) not have any significant impact in terms of your site’s performance in search results.

However it does represent a fundamental reversal in the way Google is thinking about your website content and how to prioritize crawling and indexation. Remember that up until now the desktop site was considered the primary version (similar to a canonical URL) and the mobile site was treated as an “alternate” version for a particular use case. This is why Google encouraged webmasters with a separate mobile site (m.domain.com) to implement switchboard tags (which indicated the existence of a mobile URL version with a special rel=alternate tag). Google might not even make the effort to crawl and cache the mobile versions of all of these pages, as they could simply display that mobile URL to mobile searchers.

This view of the desktop version as the primary one often meant in practice that the desktop site would be prioritized by SEOs and marketing teams and was treated as the most comprehensive version of a website with full content, structured data markup, hreflang (international tags), the majority of backlinks, etc.; while the mobile version might have lighter content, and/or not include the same level of markup and structure, and almost certainly would not receive the bulk of backlinks.