What Is Google's Mobile-First Indexing & Why Is It Important?

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Every now and then there is a bit of new information about mobile-first indexing in circulation.  It’s quite a common topic that keeps cropping up. But quite often there are misunderstandings or misconceptions as to what mobile-first indexing really is and its important role for any site.  So, let’s take a look…

Firstly Let's Clear Up the Myths Surrounding Mobile-First Indexing

Although mobile-first indexing was announced some years ago, there is is still some confusion as to what it means, what it doesn’t mean and how it should be approached.

Separate Index

There is no separate index for mobile.  It is the same index.  Mobile-first means that the mobile version of the page is crawled by Smartphone Googlebot.  It is that mobile version that is used for indexing and caching.  So the page could be a responsive mobile version, or a unique mobile URL, if a mobile version of the site is running separately.  The bottom line is that it is not mobile-only, or mobile-separate.  It just means that the first version of the site Google wishes to crawl is the mobile version.  All within the same index.

Site will deindex if no mobile version

This is not true.  If there is no mobile version of a site then Google can crawl, index and rank the desktop version.  However the lack of mobile friendliness is highly likely to impact the ability of that site to rank well.

How Do You Know if a Site is Mobile-First Indexed

An important point is that since 1st July 2019 all new sites are subject to mobile-first indexing.

From September 2020 ALL sites will be moving over to mobile-first indexing.

There are several ways to see if the site has or is moving over.

  • Increased activity and crawling by the Smartphone Googlebot.
  • Message in Search Console informing of the switch and date it happened 
  • Inspecting a URL in Search Console which details if mobile
  • Carry out a Google mobile-friendly test
Google Search Console message confirming mobile-first indexing
Mobile Indexed Message in Google Search Console

What Does Mobile-First Indexing Mean to Your Site?

There is no opt-in or opt-out.  There is no choice when to move over and no choice in any delay.

Mobile is way to go and it’s hugely important to ensure there is a fully functioning mobile version of the site. For sales it’s historically been the desktop that completes the purchase, even if mobile was used to discover the page.  Going back to 2014 only 13% of sales were completed on mobile.  There is a seismic shift in those figures and today various reports and surveys show a different picture on mobile usage.  One survey showing 62% of sales were carried out on mobile from start to finish. A clear indicator that the experience and functionality of mobile is driving its massive growth.

So it is critical a mobile version of a site is there, available to be crawled and indexed.  Although it has to be said the preference expressed by Google is a fully responsive site. Rather than a dedicated mobile second version of the site, commonly known as “m dot”, as was the common subdomain for the separate mobile version.  This is because there are known issues and potential inconsistencies having a second version kicking around.

The key points for mobile-first ready best practice, is ensuring the experience matches across both desktop and mobile:

  • Ensure both mobile and desktop contain the same content
  • Make sure Smartphone Googlebot has full access to the mobile version.
  • Keep meta robots tagging uniform across desktop and mobile
  • Keep schema structured data uniform across desktop and mobile
  • Don’t remove content from mobile for UX.
  • Keep the same headings across desktop and mobile 

Google will crawl the mobile version of the page. If there are any elements or content missing from the mobile version Google is not going to be able to access what would be available on the desktop version.  This will undoubtedly impact rankings and traffic.

Mobile-First Indexing is Not Mobile Usability

Don’t get confused between having mobile content crawled and indexed, against the mobile page being functional, effective and fully usable for the visitor.

A mobile page that is indexed in Google simply means the Smartphone Googlebot has accessed the page, can crawl it and therefore index it.  There are multiple aspects of the page that can impact load and user experience, impacting the ranking of the page.

“So, first off, again mobile usability is completely separate from mobile-first indexing. A site can or cannot be usable from a mobile point of view, but it can still contain all of the content that we need for mobile-first indexing. An extreme example, if you take something like a PDF file, then on mobile that would be terrible to navigate. The links will be hard to click, the text will be hard to read. But all of the text is still there, and we could perfectly index that with mobile-first indexing."

Key elements of a fully functional mobile page that offers very good user experience are:

  • Content Layout – ensuring content is no wider than the screen
  • Elements – ensuring elements are not too close together and too small
  • Text – ensuring the content itself isn’t to small to read
  • Theme and plugins – ensure both are compatible with mobile
  • Menus – ensure the mobile menu is formatted and clear in mobile.  Typically a burger menu.
  • Page load speed & Core Vitals


Web core Vitals and Mobile Usability

Good page speed for both desktop and mobile pages is paramount.  Caching, compression, deferring resources, image optimisation etc are all important elements to address to improve page load speed, which has a direct impact on ranking.  Come May 2021 Google will introduce another ranking aspect of page load, Web Core Vitals, which will be discussed in full another time.  At the heart of Web Core Vitals is user experience alongside page load speed.
One of the key elements is CLS (Cumulative Layout Shift) which looks at how key elements of the page shift around as the page loads.  This can be problematic for mobile pages if the responsive layout shift from desktop is not monitored and addressed.
Google has a neat video showing what can go wrong with elements shifting around!

The takeaway is that every function, rendering and layout must be thoroughly checked on mobile.  It’s simply not good enough to be ready for mobile-first indexing, if the page itself is not fully usable, or a hindrance to the user.  The usability test or the mobile usability report in Search Console should not be used as an accurate result for actual usability, according to John Mueller.  Nothing replaces physical testing of the site on different devices. 

Reference the Google Mobile-first indexing best practices document for detail on all the requirements for implementing a top quality mobile site.