Google’s John Mueller advises site owners that mobile-friendliness is not the same as ready for mobile-first indexing.
When determining whether to move a site to the mobile-first index, Google looks at criteria beyond whether the site is optimized for mobile devices.
A site could be designed for mobile and not still not be considered ready for Google’s mobile-first index if it doesn’t meet other criteria.
Mueller provided this guidance in response to a thread on Reddit titled: “Despite being mobile friendly, what could be the reasons for Google to use a desktop crawler as a primary crawler?”
Google uses different web crawlers depending on whether the site is in the mobile-first index or regular index.
Site owners can see in Search Console whether Google is using the mobile or desktop version of Googlebot to crawl a site.
Here’s an example where you can see at the top of the report it reads “Primary crawler: Smartphone”, indicating that the site has migrated to Google’s mobile-first index.
Given that most sites have been moved over to mobile-first indexing, it’s reasonable to expect to see the mobile version of Googlebot being used when checking Search Console reports.
In this case, the Reddit user’s mobile-friendly site is still being crawled with Google’s desktop crawler, which is a sure sign that it has not been migrated to mobile-first indexing.
What could be the reason for that?
Google’s John Mueller on Mobile-First Indexing
A key piece of criteria Google looks for when moving sites over to the mobile-first index is that the site shows identical content on all devices.
If the desktop version of a site’s pages has critical content that’s not shown to users on mobile devices, then the site would not be considered suitable for mobile-first indexing.
“Mobile friendly doesn’t mean it’s suitable for mobile indexing (it could be easy to use on mobile devices, but lack a lot of the content, for example).”
If you’re sure the important content is shown to users on all devices, then Mueller says not to worry.
Google’s algorithms may scrutinize a site a little too hard and hold it back from mobile-first indexing because of minor discrepancies.
“That said, if you’re sure that the content is all there on mobile, I wouldn’t sweat it. Sometimes out algorithms are a bit on the conservative side in that regard. A variation I saw a few times was that our algorithms were holding back a site because it didn’t have the same number of related items linked on the bottom of a product-page / post — yes, that’s a content difference, but you probably don’t need to care about it because it’s not going to change how your site overall is showing in search.”
However, there could be differences that actually matter in the grand scheme of things. That could include items missing from one version of a site compared to the other such as structured data, images, internal links, and so on.
“Obviously, it could also be because your site has real differences, like missing structured data, fewer significant images, bad internal linking on mobile, etc — these are things that those who don’t look deeply might miss.”
If you’re patiently waiting for Google to move your site to mobile-first indexing, and can’t figure out why it hasn’t happened yet, now you know a few more areas to check for content parity.