In a webmaster hangout on YouTube, Google’s John Mueller explained that mobile first indexing is not mobile-friendly indexing. If Google finds that the website delivers the same (or nearly the same) content for mobile devices as for desktop computers, the website will be switched to mobile-first indexing:
“Desktop only is essentially a unique form of a responsive design, right? It’s like the same design on mobile and on desktop so I could certainly see our algorithms saying well nothing breaks when we switch the site over to mobile indexing, so might as well do it.”
He explained that being indexed by the mobile bot does not mean that the website will get ranked in the mobile results:
“The other thing to keep in mind is that the mobile first indexing is not mobile-friendly indexing. So it’s not related to whether or not a site is mobile-friendly.
It’s really just the indexing part that’s switching over to mobile, the friendliness aspect is something that’s still a ranking factor in the mobile search results but it’s independent of their indexing.”
-> Mobile-friendliness is a ranking factor in the mobile search results. Even if your website gets indexed by the mobile bot, Google won’t rank it if your website isn’t mobile-friendly.
What you should do now
If you haven’t done it yet, you should make sure that your web pages work on mobile devices as soon as possible. The easiest way to support mobile devices is to use responsive website design.
Are you ready for a new mobile-friendly website?