Why are new sites automatically transitioning to mobile-first indexing?

What is mobile-first indexing and why this change?

Mobile-first indexing means that Google primarily uses the mobile version of your content to index and rank your pages. Before this shift, the desktop crawler was the reference, and the mobile version was just a secondary consideration.

Since July 2019, Google has automated this process for all new sites. No request is needed, no option to check — this is the default rule. The reason? The overwhelming majority of searches are conducted on mobile, and prioritizing desktop indexing no longer made strategic sense.

How can I check which crawler is actually indexing my site?

The Search Console may still display "Googlebot Desktop" in some reports, which can cause confusion. The reliable indicator is the URL Inspection Tool.

Open the tool, test any URL from your site, and look at the "Crawled as" section. If you see Googlebot Smartphone, your site is indeed in mobile-first indexing. This user-agent dictates what Google sees and ranks.

Does this automatic switch also apply to older sites?

No, this announcement specifically targets new sites launched after July 2019. Existing sites were gradually migrated based on their level of "mobile-readiness" — Google did not want to disrupt the ranking of a site with a poorly functioning mobile version.

For older sites, migration was conditional and notified through the Search Console. For new sites, it's automatic and non-negotiable: you start directly in mobile-first.

• Every new site launched after July 2019 is indexed in mobile-first from the start, without any manual migration.
• The Search Console may show "Desktop" in some reports, but the URL Inspection Tool reveals the true user-agent: Googlebot Smartphone.
• Existing sites have been gradually migrated based on their mobile compatibility — this announcement doesn't directly affect them.
• It's the mobile version of your content that serves as the reference for indexing and ranking, not the desktop version.

Is this statement consistent with field observations?

Yes, absolutely. Since 2019, all new projects I have audited or launched display Googlebot Smartphone in the URL Inspection Tool from the very first crawl. No exceptions. Google has kept its promise on this point.

The only trap is the confusion generated by the Search Console itself. Some reports (like the index coverage report) continue to show "Googlebot Desktop" even after the switch. The result: clients panic and think their site hasn't migrated. False signal. The URL Inspection Tool is the only reliable source.

What nuances need to be added to this rule?

The automatic switch does not absolve the need for a clean and complete mobile version. If your mobile version hides structured content, internal links, or different title/meta tags from the desktop, Google will index this degraded version. And your ranking will suffer.

Another point: Google talks about "new sites," but what exactly is a "new" site? A new domain, yes. A complete redesign on an old domain? [To be confirmed] — Google has never clarified whether a total relaunch on an existing domain triggers a reevaluation of the indexing mode. In practice, old domains remain on their initial mode until explicitly notified in the Search Console.

In what cases does this switch pose problems?

If you designed your site in a desktop-first manner with an impoverished mobile version (truncated content, overly simplified navigation, aggressive lazy-loading on images), you will lose visibility. Google indexes what it sees on mobile, period.

Sites with accordion or tabbed hidden content can also suffer if the implementation is shaky. Google crawls hidden content on mobile, but if your JavaScript fails or loads poorly, it's a lost cause.

What should be checked before launching a new site?

Make sure your mobile version contains strictly the same content as your desktop version. Texts, titles, structured tags, internal links, images with their alt tags — everything must be present. No hidden content "to enhance mobile UX." Google only crawls what is rendered.

Test your site with the URL Inspection Tool and review the mobile HTML rendering. Compare it with the desktop version. If whole sections are missing, you have a problem. Also use the Mobile-Friendly Test to check that Googlebot can execute your JavaScript and load your critical resources.

How to monitor that mobile indexing is proceeding well?

Monitor the server logs: you should see Googlebot Smartphone regularly crawling your key pages. If you only see desktop crawler activity or if mobile crawling is sporadic, dig deeper. There may be a misconfigured robots.txt, a blocked user-agent, or an issue with mobile redirections.

Also, regularly check the Search Console to ensure that no mobile indexing errors appear (blocked resources, rendering issues, inaccessible content). And cross-check with actual performance: if your traffic drops after launching, first examine the mobile version.

What mistakes should absolutely be avoided?

Never assume that Google will "understand" that your desktop version is better. It indexes mobile, period. If your mobile is a light version of your desktop, you will be ranked on this light version.

Avoid mobile redirects to a subdomain (m.example.com) if you can. Responsive design or dynamic serving are much better managed by Google in mobile-first indexing. Sites using m. often face canonicalization and content duplication problems.

• Ensure that the mobile version contains 100% of the desktop content (texts, links, structured tags).
• Test the mobile rendering with the URL Inspection Tool and the Mobile-Friendly Test before launch.
• Monitor server logs to confirm that Googlebot Smartphone is actively crawling the site.
• Avoid hidden content in accordion or aggressive lazy-loading if the JavaScript implementation is fragile.
• Regularly consult the Search Console to detect any mobile indexing errors (blocked resources, poor rendering).
• Prefer responsive design or dynamic serving over a separate mobile subdomain.