The arcane phrase means that Google will look at the mobile version of a site first when deciding how you rank in a Google search. It won’t matter if you search on a phone or a tablet or a desktop or by voice… there is now and will be only one gigantic database of websites, which Google calls its index.

Mobile-first indexing means Google predominantly uses the mobile version of the content for indexing and ranking.

In fact, all new websites created after July 1, 2019 are already indexed mobile-first. A of October 20, 2020 over half of all websites are indexed mobile-first.

So it’s time to think: how effective is your site on, for example, a phone? Because the quality of your mobile version will be the first place Google looks when ranking websites within that gigantic index.

Mobile First Indexing: what It IS

Mobile-first indexing best practices were first detailed in Google’s Developers Blog: “Mobile-first indexing means Google predominantly uses the mobile version of the content for indexing and ranking.

Make sure that Googlebot can access and render your mobile content
Make sure that content is the same on desktop and mobile
Check your structured data
Put the same metadata on both versions of your site
Check the placement of your ads”

The Google move reflects a broad shift on the Internet, where a majority of users search first on their mobile, and generally are looking at their phones as much or more than at their PC. In the words of an early tweet from @GoogleWebmasters on June 14, 2018: “It’s about time to move from desktop only and embrace mobile.”

how does mobile-first indexing affect you?

So how much does this affect you as someone who has a big stake in your or your company’s website? Will it make your site less visible on Google, even much less visible?

Maybe. There are those in the SEO world who were, especially at first, calling the change in Google’s algorithm “mobilegeddon.”

More recently, there is a bit less concern, as Google has somewhat clarified how the new algorithm works.

Time to watch your mobile site closely

The truth is, we won’t know the whole of the effect until after the transition is complete, that is, after March, 2021.

But one thing is very clear: it’s time to take a really good look, and continue to monitor your mobile site. How well it is serving and engaging your users, judged by analytics such as conversions and clicks. We highlight some best-practice in our post 10 Unbreakable Rules for Mobile Design.

Let’s take the worst case first:

It's about usability

If your mobile site is a little long in the tooth, or has not had your recent attention, then there is a chance that the new indexing system could, if indirectly, knock your ranking for a loop.

That’s not because mobile indexing is somehow inherently stricter, or biased against certain sites. It isn’t. Just being mobile indexed doesn’t affect your ranking.

It’s much simpler than that: While mobile first indexing taken by itself does not affect your rank, the usability of your mobile site definitely does. And soon your site will be held first of all to theose usability mobile standards. These, again, can be very different from those of a desktop site.

In another of its 2018 tweets, @GoogleWebmasters put it this way:

“On ranking: The mobile-first index doesn't change anything for ranking other than that the mobile content is used. While mobile-friendliness is a ranking factor on mobile, being in the mobile-first index is not.” {our emphasis].

But isn't responsive design all you need?

Suppose your site uses Responsive Design, the built-in matching feature of a WordPress or SquareSpace and others. In the Responsive world, a site on the phone, let’s say, automatically matches the content on the desktop. Are you off the hook? No worries? Not quite. The result still might not be terrific for mobile usability.

There are issues—such as font color or size—which might have been just fine on your desktop site, but can show up poorly when moving to a smaller screen.

Sorting out the two year roller coaster

Be cautioned that simply running a Google search often does not clear things up.

That’s partly because of the less-than-fulsome explanation given in the initial 2018 announcement which appeared in Google’s Inside Search blog.

Some of that first broad-brush announcement was later clarified in the series of tweets in 2018 by @GoogleWebmasters which we have cited here.

Next, the deadline for the final move to MFI, was changed. Initially set at September, 2020, Google announced in July of that year a new March 2021 deadline.

Unfortunately, there are still many undated search results out there which state the obviously obsolete initial deadline.

And as always, attempting to predict, much less fully understand Google updates is an art as well as a science. Often a matter of piecing together Google blog announcements, tweets, patent filings, third-party studies, mixed with logical deduction, it is often a matter of reading the tea leaves.

See Mobile-first indexing as a timely alert

But here is a terrific rule of thumb: one way or another, see the March 2021 deadline as a good thing, a timely alert. Make your mobile site an easy and exciting user experience starting now. You and your users will profit by it.

Hungry Monster content is always created using mobile-design best practices. See What we Offer for highlights of those offerings

Mobile-first indexing FAQ

What is mobile-first indexing as officially defined by Google:

Mobile-first indexing means Google predominantly uses 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 Search with a mobile device, Googlebot primarily crawls and indexes pages with the smartphone agent going forward.

Google developer blog

Where can I find more reliable information on mobile-first indexing?

Here are some links:

Is mobile-first indexing the same as mobile-first strategy?

No. MFI is a specific change in the way Google evaluates websites. Mobile-first strategy is an approach to designing websites.

But it is true that the two both show the growing importance of mobile design. In a mobile first strategy, a company's web presence is designed for mobile devices first and desktop second. ... Mobile first strategy also takes advantage of technology that is specific to mobile users (GPS, data-collecting, built-in cameras), to create features that are unavailable to desktop users.

Can you safely ignore the change to mobile-first indexing if your website uses Responsive Design, or Adaptive Design?

Not a good plan. Responsive Design does in most cases assure that your site complies with one of the MFI best practices, that all versions of your site match, have the same content and code. But by itself, Responsive Design does not always make for optimal mobile-friendly design.

Mitchell Miller

Google’s mobile website deadline: all about mobile-first indexing