Google Will Only Use Content From Mobile Pages if Mobile First
Google will only use the mobile version of content when a site has been moved to mobile first. If your mobile pages have less structured data or images than your desktop pages, Google will not use the content from your desktop site. Google will continue to crawl your desktop pages about 20% of the time to make sure they are not missing any new pages.
Google Recommends a Single Site for Mobile First Indexing
It’s OK to have a separate mobile website for mobile first indexing, provided it’s correctly linked from the desktop version with a mobile rel alternate and a canonical pointing to the desktop page, but Google recommends having a single URL for each piece of content with responsive design or dynamic serving in the future.
Google Determines Mobile Usability Based on The Ability to Render the Page
Google Advises Against Using Separate Mobile URLs
Having separate URLs for the mobile and desktop version of a site adds more complexity for website owners to manage, so Google recommends switching to a responsive setup.
Google Uses the Viewport Tag to Understand the Mobile-friendliness of a Page
The viewport tag is used for scaling a page for devices, and Google will use this tag to understand whether the page is mobile-friendly or not. Google won’t automatically categorise a page as a mobile version if it has a viewport tag.
Implement Redirects From Mobile Pages to Desktop Pages For Desktop Users
If you have a separate m-dot site, Google will usually pick this as the preferred canonical version after mobile-first indexing and the m-dot site will be shown in desktop search results. To avoid negative UX, implement redirects to the desktop version for desktop users.
Mobile-friendly Test Doesn’t Respond to Robots.txt Rules
When Changing a Favicon Ensure All Pages Are Updated to Display the Change
When updating a favicon for mobile search, John recommends ensuring all pages are updated and the favicon is consistent across the site, in order to display a clear signal to Google when they re-crawl the pages.
New Sites Will be on Mobile-first Indexing by Default
Google is now switching to mobile-first indexing by default for new websites.