Since March 2018 Google set a clear priority to mobile first indexing.
Mobile first indexing has created a new reality for website owners. But how does mobile first indexing is enabled? Let’s break this down step by step. We are into WordPress but most guidelines are useful for all CMS. Stay at the top of your industry by following Google’s guidelines for mobile first indexing.

Mobile-first indexing means Google has started using 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. Google isn’t creating (yet) a separate mobile-first index. They say that they will continue to use only one index.

With mobile-first indexing, Googlebot primarily crawls and indexes pages with the smartphone agent. Google actually evaluates each site individually on its readiness for mobile-first indexing based on the best practices and transition the site when the site is ready.

Google’s Guidelines

On Monday 26th March 2018, Google announced that they started migrating sites that follow the best practices for mobile first indexing.

Google’s crawling, indexing and ranking systems now they will pay warmer attention to the mobile version of the website pages, to better help mobile users find what they are looking for.

Google has already started to notify site owners that are migrating to mobile-first indexing via Search Console. Site owners will see significantly increased crawl rate from the Smartphone Googlebot. Additionally, Google will show the mobile version of pages in Search results and Google cached pages.

As always, ranking uses many factors. Google may show content to users that’s not mobile-friendly or that is slow loading if Google’s many other signals determine it is the most relevant content to show.

• Mobile-indexing is rolling out more broadly.
• Being indexed this way has no ranking advantage and operates independently from mobile-friendly assessment.
• Having mobile-friendly content is still helpful for those looking at ways to perform better in mobile search results.
• Having fast-loading content is still helpful for those looking at ways to perform better for mobile and desktop users.
• Prefer quality over quantity.
• Keep your website as clean as possible from any kind of digital noise.
• SEO guidelines apply equally both in the mobile and desktop version of your site.

Best practices for dynamic serving

As Google Developers have published them:

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 to your desktop site. This includes text, images (with alt-attributes), and videos – in the usual crawlable and indexable formats.

Structured data should be present in 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 for internationalization, 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.▸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.

Indexing Guidelines For Separate Mobile Sites

Check the following points to make sure that you have the best possible results for your mobile visitors:

• Content health status for all your website pages:
• High-quality content loads properly?
• Texts, images, videos are ok?
• alt-attributes for images are ok?
• Structured data markup on both the mobile and desktop versions of the site are the same?
• Titles and meta descriptions are equivalent?
• Social metadata are included on the mobile version as well as the desktop version?
• Have you verified both desktop and mobile version in Google Search Console?
• Have you checked if your server can handle increased crawl rate?
• Have you included the structured data markup in both versions?
• Your trust signals are easy to find and read in both versions? (privacy policy & terms of use)
• Check your website after any major Google’s algorithm update

Last tip: make sure your mobile version has all the high-quality, valuable content that exists on your desktop site.