What Is Mobile-First Indexing, and What Does It Mean for Your Site?

Apr 28, 20179 min read

Illustration of mobile-first indexing: a phone showing search results in front of a desktop monitor, with a crawler robot and index cards

Google ranks your pages by what’s on their mobile version, even when the person searching is sitting at a desktop. Mobile-first indexing, as Google calls it, means its smartphone Googlebot crawls those mobile pages and uses them to decide what each page is about and how it ranks. And it isn’t upcoming anymore. Google started moving sites over in 2018 and confirmed the switch was complete in October 2023.

We first wrote about this change in 2017, when it was still on the horizon. This updated guide keeps what we said then as history and adds what matters now. If your mobile pages show less content, structured data or images than your desktop pages, Google sees less of your site.

What is mobile-first indexing?

Google has traditionally relied on the desktop version of websites to crawl, index and present content in search engine results pages (SERPs). Mobile-first indexing turns that on its head. Google now crawls and indexes content based on what’s rendered for smartphones. In Google’s own words, it uses “the mobile version of a site’s content, crawled with the smartphone agent, for indexing and ranking,” as its mobile-first indexing best practices explain.

Is there a separate mobile index?

No. The phrase “mobile-first index” suggests a second index, but Google still keeps one index. “Mobile-first” describes which version of a page Google reads. The smartphone crawler is now the primary visitor, and the desktop crawler is only used occasionally.

Is mobile-first indexing a ranking factor?

Not on its own. Mobile-first indexing changes which version of your content gets evaluated, not how the ranking systems score it. The effect on rankings comes from what the mobile version contains. If content, headings or structured data are missing on mobile, Google can’t use them. Mobile usability is a separate consideration that sits within Google’s page experience guidance.

A brief history: why Google went mobile-first

Google’s indexing process came well before the rise of mobile devices. When feature phones (remember the wildly popular Motorola Razr?) first started connecting to the internet and rendering websites, Google created Googlebot-Mobile to crawl them and the first generation of mobile sites designed for feature phones. The next evolution was smartphones: iPhone, Android and Windows Phone. The internet responded with websites designed specifically for smartphones, through mobile subdomains and responsive design.

Googlebot-Mobile crawled early smartphone-friendly websites as well. But the capabilities of smartphones soon led to websites with logins, video, social sharing, e-commerce and more, and Google had to adapt its mobile crawlers again. In 2015, Google reached a milestone: more searches were conducted on mobile than on desktop. That shift is what pushed Google to evolve its core product once more. For the wider story of how mobile reshaped search, see our connected history of Google, mobile SEO and rankings.

When did mobile-first indexing happen? The timeline

The rollout took far longer than anyone expected in 2017. Experiments started in late 2015, and Google had hoped to roll the change out worldwide by late 2016. In April 2017, at an SEO conference, Google representatives were hoping it would happen by the end of 2017, though even then it wasn’t likely. Here’s how it actually unfolded:

2015: Mobile searches overtake desktop searches, and Google launches its mobile-friendly update.
November 2016: Google announces mobile-first indexing and begins experimenting.
March 2018: After a year and a half of testing, Google starts migrating sites that follow its best practices.
March 2020: Google says 70% of sites shown in its results have already shifted and plans to switch the whole web starting September 2020. That deadline was pushed back more than once.
October 2023: Google declares the move complete. A very small set of sites that don’t work on mobile at all are still crawled with the legacy desktop Googlebot for now.
December 2023: Google retires the Mobile-Friendly Test and the Search Console Mobile Usability report, pointing site owners to tools like Lighthouse instead.

What we told readers in 2017

When this post first ran in April 2017, the change was still on its way. Our advice then holds up well, so here it is, lightly edited.

What was changing?

With mobile search now the dominant behavior, Google wanted its core product to consider the smartphone first. It would crawl and index content based on the mobile version of websites, even when the person searching was on a desktop device. It wasn’t as scary as it sounded.

What would happen to rankings?

This question was the reason for the delay, and the first reason to breathe a sigh of relief. Google wanted no significant change in search results and rankings, as close to net-zero as possible. With more websites adopting responsive design, that made sense. A responsive site serves the exact same content to mobile and desktop users, so how Google crawls, interprets and ranks that content shouldn’t change. Websites that weren’t mobile-friendly would still be crawled the same way.

What should you do?

If your site wasn’t mobile-friendly, that was the second reason not to panic. You wouldn’t disappear from search or see drastic drops in traffic, because if no mobile version was detected, Google would still crawl, index and rank what you had. But it was time to start planning a modern site for mobile users.

Smartphone penetration (the share of phone owners with smartphones rather than feature phones) had passed 88% in the U.S. in 2016. There was also a growing shift, especially among younger people, toward smartphones as their primary browsing device. Add studies showing that poor experiences on non-mobile-friendly sites led to higher bounce rates, lower conversion rates and lower brand trust, and there were good reasons to finally update.

If your site was mobile-friendly, we advised double-checking what content it served. Many mobile sites were designed to show less content than their desktop counterparts, to keep the experience focused on what people came to do. Under a mobile-first index, hidden content was at risk of not being crawled, which could affect what surfaced in search results on any device. That’s why responsive design is widely recommended, and why we build our sites responsively here at Daylight.

What does mobile-first indexing mean for your site today?

Now that every working site is indexed from its mobile version, the job is making sure the mobile version is complete. Google’s best practices come down to a few areas.

Content parity

Your mobile pages should contain the same primary content as your desktop pages, with the same clear headings. A different mobile design is fine. Google specifically says you can move content into accordions or tabs to save space, as long as the content is equivalent. What hurts is removing it. If the mobile page has less, expect some traffic loss, because Google has less to work with.

Structured data and metadata

If you use structured data, it needs to be on the mobile version too, with URLs that point to the mobile pages. Google suggests starting with Breadcrumb, Product and VideoObject markup if you have to prioritize. Title elements and meta descriptions should also be equivalent across versions.

Images and video

Use high-quality images on mobile, not low-resolution substitutes, in supported formats. Keep the same alt text, captions, titles and file names on both versions, and avoid image or video URLs that change on every page load. Using the same image URLs across desktop and mobile avoids a temporary dip in image search traffic. For video, use supported tags and place the video where mobile visitors can find it without excessive scrolling.

Lazy-loading

Lazy-loading images and sections speeds up mobile pages, but Google won’t load content that only appears after a swipe, click or typing. Don’t lazy-load primary content on user interaction, and follow Google’s guidance to make sure lazy-loaded content is visible to its crawler, for example by loading it when it enters the viewport.

Robots tags, resources and separate mobile URLs

Use the same robots meta tags on mobile and desktop. A stray noindex on the mobile version can drop a page from the index. Don’t block mobile CSS, JavaScript or image files in robots.txt. If you run a separate m-dot site, make sure every desktop page has an equivalent mobile page, error statuses match, mobile URLs don’t rely on # fragments, and pages don’t all redirect to the mobile home page.

Does responsive design solve mobile-first indexing?

Mostly, yes. Google recommends responsive web design because it serves the same HTML on the same URL to every device, so content and metadata are identical by default. Dynamic serving and separate mobile URLs still work, but they’re where most parity problems come from. Our post on responsive grid layouts covers how those layouts evolved.

Responsive doesn’t automatically mean usable, though. Indexing is about what Google can read. Mobile-friendliness is about whether people can comfortably use the page. For the design side of that, read why mobile isn’t going anywhere. Our technology and development team builds for both.

How to check your site for mobile-first indexing

In 2017, the easy first step was to test a few pages with Google’s Mobile-Friendly Test tool. That tool was retired in December 2023, but checking is still straightforward:

Inspect key URLs in Search Console. The URL Inspection tool shows how Googlebot smartphone last crawled a page and lets you view the rendered HTML and screenshot.
Review the crawl stats report in Search Console settings to see how your site is being crawled.
Run Lighthouse. Lighthouse, built into Chrome DevTools and PageSpeed Insights, audits mobile performance, accessibility and SEO basics.
Compare mobile and desktop side by side. Check that body copy, headings, internal links, structured data, images and alt text all appear on the mobile version.
Use the site on a real phone. Tap through menus, forms and accordions the way a customer would.

What if my site isn’t mobile-friendly?

Your site won’t vanish from search. Google says having a mobile version isn’t required for inclusion in results, though it’s very strongly recommended, and the few sites that don’t work on mobile at all are still crawled with the legacy desktop crawler for the time being. But Google also says it will keep reducing desktop crawling, and the bigger cost is your visitors: most of them arrive on a phone. If a site doesn’t work well there, it’s time to have that conversation and consider updating.

What Is Mobile-First Indexing, and What Does It Mean for Your Site?