What Is Mobile-First Indexing?
Mobile-first indexing means Google uses the mobile version of a page’s content for indexing and ranking. The page that Googlebot Smartphone sees, with its text, images, links, structured data, and metadata, is the page Google evaluates, including for people searching on desktop. If your mobile page carries less than your desktop page, Google works from the smaller version.
How Google Got Here
In November 2016, Google wrote that its ranking systems “still typically look at the desktop version of a page’s content” and that “we’ve begun experiments to make our index mobile-first.” In a March 2020 post it wrote: “To simplify, we’ll be switching to mobile-first indexing for all websites starting September 2020.” The switch took longer than that. In its October 2023 post “Mobile-first indexing has landed”, Google said it knew of “a very small set of sites which do not work on mobile devices at all,” naming the error types it saw: pages that show errors to all mobile users, a mobile site blocked by robots.txt while the desktop site is crawlable, and mobile sites that redirect every page to the homepage.
Seeing Googlebot Desktop in your logs is not a sign that your site was left behind. Google’s Googlebot documentation states that “the majority of Googlebot crawl requests will be made using the mobile crawler, and a minority using the desktop crawler.” It also notes that both crawlers obey the same robots.txt token, so you cannot target one and not the other in robots.txt.
Three Ways to Serve Mobile and Desktop
Google’s mobile-first indexing best practices describe three configurations.
| Configuration | How it works | What it depends on |
|---|---|---|
| Responsive web design | One URL and one HTML document for every device; CSS adapts the layout | Nothing extra; there is one version to keep correct |
| Dynamic serving | One URL; the server returns different HTML by device | User-agent detection and the <!–INLINECODE0–> HTTP response header |
| Separate URLs (m-dot) | Different URLs for mobile and desktop | User-agent and <!–INLINECODE1–> headers to send each device to its version, a <!–INLINECODE2–> link from the desktop page and a canonical from the mobile page back to it, plus matching settings on both sites |
The documentation is direct about the choice: “Google recommends Responsive Web Design because it’s the easiest design pattern to implement and maintain.” The rest of its guide applies to the other two configurations, because they are the ones where the two versions can drift apart.
What Has to Match
Google’s checklist comes down to one instruction: “Make sure that your mobile site contains the same content as your desktop site.” In practice that covers:
- Primary content. Text, images, and video should be on both versions. Design can differ; the documentation allows “moving content into accordions or tabs” on mobile, “just make sure that the content is equivalent to the desktop site, since indexing on your site comes from the mobile site.”
- Structured data. “Make sure that your mobile and desktop sites have the same structured data.” Markup that exists only on desktop drops out of what Google indexes.
- Metadata. “Make sure that the title element and the meta description are equivalent across both versions of your site.”
- Images. Google’s guidance: “Use the same titles, captions, filenames, and text relevant to the images on the mobile site as you do for the desktop site.”
- Lazy loading. “Don’t lazy-load primary content upon user interaction.” Content that appears only after a tap, swipe, or typed input may never be seen; Google’s separate guidance on fixing lazy-loaded content explains the methods that do work.
For separate-URL sites, the documentation adds checks of its own, including that the error page status is the same on both the desktop and mobile sites.
Mistakes That Show Up on Mobile Only
These are the failures the 2023 post and the best practices page point to:
- robots.txt rules that block the mobile site, or the CSS, JavaScript, and images it needs to render
- a
noindextag, a broken canonical, or an error status that exists only on the mobile version - mobile pages that redirect to the homepage instead of their own equivalent
- content, structured data, or image text that was trimmed from the mobile template
Each of these tells Google something different about the page than the desktop version does, and the mobile version is the one Google reads.
Checking Your Own Site
The URL Inspection tool in Search Console has a “Crawled as” field, described as “the user agent type used for the crawl (desktop or mobile),” alongside the URL’s index status and the Google-selected canonical. Inspect one page from each template you use (home page, an article, a product or category page) and compare the rendered result with what a phone visitor sees. For a site-wide view, the Page indexing report groups URLs that are not indexed by reason, which is how a template-level problem, such as a mobile-only noindex, becomes visible.
Search Console no longer has a separate mobile usability report. Google’s documentation changelog has this entry for December 1, 2023: “Removed mentions of the Mobile Friendly Test and the Mobile Usability report throughout our documentation, as they are going away.”