Google have seen some confusion around their mobile first indexing signals and in a series of tweets clarified them. The main thrust of the tips is that if you have desktop content and mobile content then Google will be indexing your mobile content and giving this priority. That means if you have additional content on your desktop site compared to your mobile site it will be given much lesser importance in search results and you’ll get less traffic.
This makes sense, as so much of the world uses a mobile as their primary browsing platform and there’s no point sending them to a highly relevant search result just for them to discover that they can’t see the content of interest.
Google mobile first indexing signals clarifications
URLs in search
With Mobile-first indexing, we index the mobile version. When we recognize separate mobile URLs, we’ll show the mobile URL to mobile users, and the desktop URL to desktop users – the indexed content will be the mobile version in both cases.
Crawled counts
The total number of crawled URLs/day generally won’t change, but the balance will shift from mostly-desktop to mostly-mobile crawls. During a switch-over to mobile-first indexing we may temporarily crawl more as we reindex everything.
Cached page
Unfortunately, it looks like we’re currently still not showing a cached page for many mobile-first indexed sites. This is a bug, not by design, and should get resolved over time. It’s just the UI, it doesn’t affect crawling, indexing, or ranking.
Speed and mobile-first indexing
The mobile speed update in July is independent of mobile-first indexing. Fast sites are awesome for users, especially on mobile, since devices & connections there tend to be slower than with desktops.
Mobile website UIs
Using “hamburger-menus” [the three line menu icon familiar on mobile sites] and “accordions” [collapsible content revealed by clicking on headers] on mobile websites is fine.
On ranking
The mobile-first index doesn’t change anything for ranking other than that the mobile content is used. While mobile-friendliness is a ranking factor on mobile, being in the mobile-first index is not.
In case you’re curious, our docs on mobile-first indexing are at https://webmasters.googleblog.com/2016/11/mobile-first-indexing.html, https://webmasters.googleblog.com/2018/03/rolling-out-mobile-first-indexing.html, https://developers.google.com/search/mobile-sites/mobile-first-indexing, and https://developers.google.com/search/mobile-sites/ for mobile sites in general.
– Google Webmasters via twitter
