The Complete Guide to Mobile First Indexing.

What is the Mobile-First Index?

Mobile-first indexing means Google predominantly uses the mobile version of a page’s content for indexing and ranking, whereas previously, the index primarily used the desktop version of a page’s content when evaluating the relevance of a page to a user’s query.

In other words, when it comes to performing well in the SERPs, it’s the mobile version of your site Google’s looking at.

What do we know about the mobile first index?

It might seem like a lifetime ago, but it was in 2016 that Google first announced their plans for mobile-first indexing (MFI). Google spent years transitioning the web to MFI until they announced in early 2020 that they’d be “switching to mobile-first indexing for all websites starting September 2020.”

Botify closely monitored this transition so that we could find out what sites Google transitioned first and which sites were helped or hurt by the transition.

To do this, we evaluated:

  • Billions of Googlebot crawls
  • Millions of URLs
  • Hundreds of unique domains in a variety of sizes and industries

Keep reading to find out what we learned, and how you can optimize your site for our new reality… the mobile-first index.

How did Google move sites over to the mobile-first index?

As of July 2019, more than a third of websites still had not been moved over to mobile-first indexing. In March 2020, Google announced the number had grown closer to 70%. The transition was slow, but steady.

So what did that look like?

Back in June 2018, when we first started pulling the data, just 9.6% of websites had been transitioned to mobile first

indexing. By October of 2018 though, that number had risen to 34% of all websites in our database.

But let’s break that down further.

What are the characteristics of the sites Google transitioned first?

Publishers led retail and marketplace websites in the transition to MFI.

Out of all the industries we evaluated, publishers comprised the largest share of sites that had moved to mobile-first indexing. As of July 2019, 73% of publisher sites had been moved over, compared to 62% of retail (e-commerce) websites and 52% of classifieds (marketplace) websites.

Publisher websites also experienced the most gains since October 2018, with an 11% increase in sites that had moved over to mobile-first indexing, compared to a 9% increase for marketplace websites and a 7% increase for retail websites.

Why does the MFI seem to love publishers?

While no one can know for sure, we do know that a trademark of publisher websites is that they consistently publish fresh content. Consequently, these sites may be crawled better because of that freshness, and from our data, sites with better crawl ratios are more likely to be moved over to mobile-first indexing.

Initially, a greater percentage of responsive websites moved over to mobile-first indexing than non-responsive websites.

About 65% of responsive websites we analyzed had been moved over to mobile-first indexing, compared to about 52% of non-responsive websites. Non-responsive websites in our study were using either separate mobile URLs or dynamic serving.

Smaller websites entered the mobile-first index at a faster rate than larger websites.

Through our research, we found a definite correlation between website size and mobile-first indexing. For example, among our analyzed sites with less than 10,000 URLs, 70% had been moved over to mobile-first indexing. Among sites with more than 10 million URLs, 50% had been moved over to mobile-first indexing.

There are many possible reasons for this correlation. Potentially, Google gave the largest sites the longest to prepare, or possibly moved large sites over at a slower pace to ensure a successful transition. Looking at this from a risk assessment point of view, this would make sense. Smaller websites should theoretically be easier both for the stakeholders to prepare for mobile-first indexing and easier for Google to transition to mobile-first indexing.

What’s the difference between responsive, mobile URLs, and dynamic serving?

All three are options for creating mobile versions of your web pages.

  • Responsive is Google’s recommended design pattern. It serves the same page, but adapts it to fit any screen size.
  • Mobile URLs means that the website has mobile-specific URLs that are different than their desktop URLs.
  • Dynamic serving is when the server uses code specific to the user agent requests on the page (mobile, tablet, or desktop), but the URL remains the same.

Very slow loading websites were transitioned to mobile-first indexing at a slower rate.

Did load times impact how quickly Google transitioned sites to mobile-first indexing? Maybe. While our data revealed little difference between sites that loaded in <1500ms, 1000ms, and 500ms, a noticeably lower percentage of websites that took longer than 2000ms to load had been transitioned over.

We also tried to find correlations between mobile first indexing and other SEO indicators to no avail

There were plenty of SEO indicators that we thought may have an impact on how quickly a site was moved over to mobile-first indexing, but actually had no correlation.

The SEO indicators that had no correlation with being moved to mobile-first indexing were:

  • The ratio of content to template content
  • Organic search visits
  • Outlinks
  • Language
  • Mobile traffic share
  • Mobile vs. desktop content visibility

What does “average load time” mean?

Average load time refers to the delay between the moment the Botify crawler requested the URL and the moment the page’s HTML code was fully downloaded.

What can we learn from mobile-first indexing’s winners and losers?

While some sites that transitioned to mobile-first indexing experienced improvement in their key KPIs, other sites experienced major losses. The key differentiator seemed to be, overwhelmingly, content parallelism between desktop and mobile versions.

The website whose KPIs you see on the top row had high content parallelism between their desktop and mobile versions, while the site in the bottom row had high dissimilarity between the two versions.

The key takeaway here is that if you want to succeed in the transition to mobile-first indexing, you need to make sure your mobile version matches your desktop version.

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Learn how Botify can help you optimize for the Mobile-First Index

When real estate company Logic Immo detected in LogAnalyzer that their site was starting to be crawled more and more by Googlebot Smartphone, they knew their time to transition to mobile-first indexing had come.

Read the Case Study