Is it true that mobile-first indexing applies to every site without exception?

What exactly is mobile-first indexing?

Mobile-first indexing means that Googlebot primarily crawls and indexes the mobile version of your site, even for desktop users. Historically, Google indexed the desktop version and used that base to rank all queries. Now, it's the opposite: the mobile version becomes the primary source.

This switch is not theoretical. When your site migrates, Google no longer considers your desktop version to assess relevance, content, or ranking signals. If your mobile version lacks content, structured data, or internal links present on desktop, those elements disappear from the index.

Why is Google pushing all sites towards this model?

The main reason relates to user behavior: the majority of searches have been conducted on mobile devices for several years. Prioritizing the indexing of the desktop version no longer made sense when 60 to 70% of traffic came from smartphones.

Google wants its index to reflect what users actually see. If a mobile user lands on a stripped-down mobile page while Google indexed a rich desktop version, the experience is disappointing. Mobile-first indexing aligns the index with the actual browsing reality.

Will all sites really be migrated without exception?

Yes, that is the stated objective. Google started this gradual migration several years ago and continues to switch sites in waves. Newer sites are generally migrated right from the start, while older ones follow over time.

You will receive a notification in Google Search Console when your site switches. This notification confirms that mobile Googlebot becomes your primary crawler. No manual action is required on your part to trigger the migration — Google decides based on internal criteria (mobile quality, content parity, etc.).

• The mobile version becomes the reference index, even for desktop searches.
• Google Search Console sends a notification when the switch occurs.
• All sites will eventually be migrated, according to a gradual timeline determined by Google.
• Content parity between mobile and desktop is critical to avoid losing visibility.
• Structured data, images, and metadata must be identical across both versions.

Is this statement consistent with what we observe in practice?

Yes, totally. Sites that have switched to mobile-first indexing show ranking variations directly linked to the quality of their mobile version. We often see sites lose positions because their mobile version hides content, displays fewer images, or removes internal links present on desktop.

Crawling tools like Screaming Frog or OnCrawl confirm these discrepancies: some responsive sites have subtle differences (poorly configured lazy loading, content in non-crawlable accordions), while others with a separate mobile version (m.site.com) display significantly less text or entire sections.

What are the gray areas that Google does not clarify here?

Mueller does not provide any specific timeline for the migration of the last sites. Some sites are still waiting for their switch several years after the initial waves. Google does not communicate the exact criteria that trigger migration — it is presumed that mobile/desktop parity plays a role, but nothing official. [To be verified]

Another unclear point: what happens to sites that objectively do not need a mobile version (complex online tools, B2B platforms desktop-only)? Google claims to want to migrate "all sites", but some use cases remain unsuitable for mobile. No official exceptions have been documented publicly.

In what situations does this rule pose practical problems?

Sites with different mobile and desktop versions (m.site.com vs www.site.com) are the most exposed. If the mobile version was developed as a lightweight subset of the desktop version, transitioning to mobile-first indexing can result in a dramatic drop in traffic.

Sites with hidden content in accordions or tabs on mobile also raise questions. Google claims to crawl this content, but tests show that the SEO weight given to content visible immediately is higher than that of content hidden behind a click. Let's be honest: we still lack reliable data on the actual impact of these patterns on ranking post-migration.

What should you prioritize checking on your mobile site?

First reflex: consistently compare the text content between your mobile and desktop versions. Use the URL inspection tool in Search Console, select "mobile version" and compare the rendered HTML with the desktop version. Any text, images, or links present on desktop should also appear on mobile.

Next, check your structured data. Schema.org must be identical on both versions. Many sites forget to deploy the same markups on mobile, thinking that only the desktop version matters. This is false. Google now reads only the mobile version to build its rich snippets.

What common mistakes should you absolutely avoid?

Classic mistake: poorly configured lazy loading of images that prevents Googlebot from discovering them. If your images only load upon user scroll and Googlebot does not simulate this scroll, they become invisible to the index. Test with the Search Console inspection tool.

Another trap: removing internal links on mobile to streamline the interface. The result: your internal linking collapses, internal PageRank circulates less efficiently, and some deep pages lose visibility. Keep the same links, even if you have to place them in an accessible hamburger menu.

How can I check if my site is ready for mobile-first indexing?

Use Google’s mobile-friendly test tool as a first filter. Then, move on to the real-world test: crawl your site with Googlebot smartphone using Screaming Frog or a similar tool. Compare the number of pages, images, and links found with a desktop crawl.

Regularly consult Search Console: the "Coverage" tab tells you if any pages are excluded due to mobile issues. If you see errors like "Blocked by robots.txt" or "Not found (404)" specific to mobile, correct them immediately. And this is where it often gets stuck.

• Compare the rendered HTML content between mobile and desktop via Search Console
• Ensure that all Schema.org structured data is present on mobile
• Test the lazy loading of images with the URL inspection tool
• Validate that the mobile internal linking structure is equivalent to the desktop
• Crawl the site in Googlebot smartphone mode and compare it with desktop
• Monitor Search Console for any alerts or migration notifications