Google Mobile-First Indexing (26 March 2018): What Changed and How to Fix Issues

Google mobile-first indexing is the change that made Google use the mobile version of a page, instead of the desktop version, for indexing and ranking. After about 18 months of experiments, the broad rollout began on 26 March 2018, and Google declared the transition complete in October 2023. It was never a ranking boost: it changed which version of your page Google reads, so sites whose mobile pages were missing content lost out.

See how it fits with other changes in my full list of Google algorithm updates.

What mobile-first indexing changed

Google put it plainly: "Mobile-first indexing means that we’ll use the mobile version of the page for indexing and ranking." Before this, Google mostly crawled and evaluated the desktop page, even when the searcher was on a phone.

Three points are often misunderstood:

• There is still one index. Google did not create a separate mobile index. Only the version of the page it crawls and indexes changed.
• It is not a ranking boost. Mobile-friendly pages did not jump up because of it. What changed is that anything missing from your mobile page effectively became invisible to Google.
• Crawling shifted to Smartphone Googlebot. Migrated sites saw a significantly increased crawl rate from Smartphone Googlebot, which is often the first sign in server logs.

Timeline

Who was affected

Sites with responsive design, where the same HTML is served to every device, were largely unaffected. The sites at risk were those whose mobile versions had less than their desktop versions:

• Separate m-dot sites (m.example.com) with shortened articles or missing sections.
• Dynamic serving setups that dropped structured data, reviews or related links on mobile.
• Mobile templates without the same title tags, meta descriptions or hreflang annotations.
• Sites blocking CSS, JavaScript or images from Googlebot in robots.txt, so the smartphone crawler could not render the page properly.

A typical example: an ecommerce site that hid product descriptions and specification tables on mobile to keep the page short. Once Google indexed the mobile version, that text no longer helped the product pages rank.

How to tell if mobile-first indexing hit your site

Unlike most updates, there was no single date to compare against. Each site moved when Google migrated it, so diagnosis starts with finding your own migration date.

1. Find your switch date. Google sent migration notices in Search Console. Server logs showing a jump in Smartphone Googlebot requests also mark the change.
2. Compare around that date, not around 26 March 2018. Look at the two weeks before and after your own migration.
3. Diff mobile and desktop. Load key pages in both versions and compare main content, headings, internal links, images and alt text, structured data and metadata.
4. Test rendering as Google sees it. Use the URL Inspection tool in Search Console to view the crawled page and check blocked resources.
5. Look at structured data reports. A drop in valid items after migration is a strong sign that mobile pages lack the markup.

How to recover from mobile-first indexing problems

This is the most fixable change on this list, because the cause is concrete: Google is reading a weaker version of your page. Make the mobile version complete and the problem goes away as Google recrawls.

If you run a separate mobile site or a heavy JavaScript front end, this is technical work best done with a crawl comparison of both versions. My technical SEO services include that comparison, and a move to responsive design is often part of an SEO-friendly web design project.

Is it still relevant today?

Completely. Mobile-first indexing is now the default for the whole web, and Google declared the transition complete in October 2023. Every page you publish is judged on its mobile version. If something matters for ranking, such as copy, links, structured data or images, it must be on the mobile page.

Frequently asked questions

Sources

• Google Search Central Blog: Rolling out mobile-first indexing
• Search Engine Land: Google begins rolling out mobile-first index
• Keywords Everywhere: Mobile-first indexing
• Ignite Visibility: Google update history

If you suspect your mobile pages are telling Google less than your desktop pages, request a free audit. My SEO audit compares both versions page by page and lists exactly what is missing.