Best practices for mobile-first indexing

Mobile-first indexing means Google will predominantly use the mobile version of the content for indexing and ranking. Historically, the index primarily used the desktop version of a page's content when evaluating the relevance of a page to a user's query. Since the majority of users now access Google via a mobile device, the index will primarily use the mobile version of a page's content going forward. We aren't creating a separate mobile-first index. We continue to use only one index.

With mobile-first indexing, Googlebot primarily crawls and indexes pages with the smartphone agent. We will continue to show the URL that is the most appropriate to users (whether it's a desktop or mobile URL) in Search results.

As we said, we transition sites slowly to ensure a good experience for site owners and users. We evaluate each site individually on its readiness for mobile-first indexing based on the best practices and transition the site when the site is ready.

What's changing

If you have this type of site...
Desktop only Your site is desktop only and doesn't have a mobile-friendly version.	No change. The mobile version is the same as the desktop version.
Responsive web design Your site adjusts for screen size.	No change. The mobile version is the same as the desktop version.
Canonical AMP All your web pages are created in AMP HTML.	No change. The mobile version is the same as the desktop version.
Separate URLs Each desktop URL has an equivalent different URL thatserves mobile-optimized content. This site type is also known as an m-dot site.	Google prefers the mobile URL for indexing. To prepare for mobile-first indexing, follow our best practices.
Dynamic serving Your site serves different content based on the user's device. Users only see one URL.	Google prefers the mobile optimized content for indexing. To prepare for mobile-first indexing, follow our best practices.
AMP and non-AMP Your site has both AMP and non-AMP versions of a page. Users see two different URLs.	Google prefers the mobile version of the non-AMP URL for indexing. If your non-AMP mobile version uses dynamic serving or separate URLs, follow our best practices.

Best practices for dynamic serving and separate URLs

If your site has separate desktop and mobile content, which means you have a dynamic serving or separate URLs (or m-dot) site, make sure you follow the best practices below to prepare for mobile-first indexing:

• Your mobile site should contain the same content as your desktop site. If your mobile site has less content than your desktop site, you should consider updating your mobile site so that its primary content is equivalent with your desktop site. This includes text, images (with alt-attributes), and videos – in the usual crawlable and indexable formats.
• Structured data should be present on both versions of your site. Make sure URLs in the structured data on the mobile versions are updated to the mobile URLs. If you use Data Highlighter to provide structured data, regularly check the Data Highlighter dashboard for extraction errors.
• Metadata should be present on both versions of the site. Make sure that titles and meta descriptions are equivalent across both versions of your site.

Additional best practices for separate URLs

If your site has separate URLs (also known as m-dot), there are additional best practices you should follow.

• Verify both versions of your site in Search Console to make sure you have access to data and messages for both versions. Your site may experience a data shift when Google switches to mobile-first indexing for your site.
• Check hreflang links on separate URLs. When you use rel=hreflang link elements forinternationalization, link between mobile and desktop URLs separately. Your mobile URLs' hreflang should point to mobile URLs, and similarly desktop URL hreflang should point to desktop URLs.
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  Example of hreflang for separate URLs
• Ensure your servers have enough capacity to a handle potential increase in crawl rate on the mobile version of your site.
• Verify that your robots.txt directives work as you intended for both versions of your site. The robots.txt file lets site owners specify which parts of a website may be crawled or not. In most cases, sites should use the same directives for both mobile and desktop versions of their sites.
• Make sure you have the correct rel=canonical and rel=alternate link elements between your mobile and desktop versions.

Resource URL: https://developers.google.com/search/mobile-sites/mobile-first-indexing