To recap, currently our crawling, indexing, and ranking systems typically look at the desktop version of a page’s content, which may cause issues for mobile searchers when that version is vastly different from the mobile version. Mobile-first indexing means that we’ll use the mobile version of the content for indexing and ranking, to better help our – primarily mobile – users find what they’re looking for. Webmasters will see significantly increased crawling by Smartphone Googlebot, and the snippets in the results, as well as the content on the Google cache pages, will be from the mobile version of the pages.
As we said, sites that make use of responsive web design and correctly implement dynamic serving (that include all of the desktop content and markup) generally don’t have to do anything. Here are some extra tips that help ensure a site is ready for mobile-first indexing: