Google crawls and ranks your site from the mobile version of your pages. Content that only exists on desktop does not count.
Mobile-first indexing means Google crawls, renders and ranks your site using the mobile version of your pages, not the desktop version. Since October 2023 it applies to every site in the index, with no opt out. If content exists on desktop but not on mobile, as far as Google is concerned it does not exist.
What actually changed
Google started testing this in 2016 and finished the rollout in 2023. There is no separate desktop index any more. Googlebot Smartphone does the crawling, the mobile render is what gets stored, and the ranking signals come from that version.
For a responsive site this is mostly a non event. One URL, one set of HTML, the layout shifts with CSS. The risk sits with sites that serve genuinely different markup to different devices, whether through a separate m. subdomain, dynamic serving, or a responsive build that strips chunks of content out below a breakpoint.
Where sites lose content
The usual culprit is display none applied to a whole section rather than a decorative element. Sidebars, related product grids, long form copy under a heading, full spec tables swapped for a two line summary. Google does read content behind tabs and accordions, so that pattern is safe. Content removed from the mobile DOM entirely is not.
Structured data is the second common gap. A team adds schema to the desktop template, then forgets the mobile template renders from a different partial. Review stars, prices and FAQ markup disappear from results and nobody connects the drop to a layout change made three months earlier.
Internal links are the third. Mobile navigation gets trimmed for space. If your category links only live in a desktop mega menu, the pages below them lose most of their internal link equity and start drifting down the results.
Checking your own templates
Set your browser user agent to Googlebot Smartphone and load your key templates. Then run the same URLs through URL Inspection in Search Console and read the rendered HTML. You are looking for three things. Is the body copy the same. Is the structured data present. Are the internal links there.
Do this per template, not per page. A homepage, a category, a product or service page, an article, plus anything unusual you run. Five checks normally surfaces everything a thousand page crawl would, because these faults live in templates.
Speed counts on the mobile version too
Because the mobile page is the ranked page, mobile Core Web Vitals are the ones that matter. Largest Contentful Paint on a mid range Android over a 4G connection, not on your laptop over office broadband. Test with throttling on or the numbers will flatter you. This is routine work in any technical SEO engagement and it is usually where the quickest wins sit.
Related reading: our guides to JavaScript SEO, page speed, Googlebot, getting Google to index your pages, Cumulative Layout Shift and web crawlers.
Common questions
Does mobile-first indexing mean desktop rankings do not matter?
Desktop rankings still exist and still send traffic. What changed is where the signals come from. Google works those rankings out from the mobile version of the page, so a weak mobile experience drags desktop positions down with it.
Should I still run a separate mobile site?
No. Separate m. subdomains create duplicate content, split link signals and double the maintenance. If you have one, plan a move to responsive. If you are building something new, responsive is the sensible default.
Is it safe to hide content in tabs or accordions on mobile?
Yes, as long as the content sits in the HTML. Google indexes collapsed content and treats it normally. The line to watch is content removed from the page source for small screens, which is a different thing entirely.
How do I know if my site has already been affected?
Check the crawl stats report in Search Console settings to confirm Googlebot Smartphone is doing the work. If rankings fell after a design refresh, compare the mobile and desktop rendered HTML from before and after that release.
