Why does Google show both the mobile and desktop versions of your pages in its results?

What does this URL duplication in the SERPs really mean?

When you search for your brand or main keywords and see both example.com/page and m.example.com/page appearing, it's not a Google bug. It's the direct symptom of a canonical configuration issue between your mobile and desktop versions.

This situation reveals that Googlebot does not know which version to prioritize. Without clear directives, the engine indexes both variants and treats them as separate pages. The result: you are cannibalizing your own traffic and fragmenting your ranking signals between two URLs that should be unified.

How does Google typically determine which version to display?

With the rollout of Mobile-First Indexing, Google defaults to using the mobile version of a page for indexing and ranking. But this logic only works if the canonical tags are properly set up in both directions.

The mobile page should canonically point to the desktop version (link rel="canonical" href="https://www.example.com/page"), while the desktop page should have a link alternate media pointing to the mobile version. This dual signaling helps Google understand that both URLs represent the same content and allows it to index only one.

Why is this configuration so often poorly implemented?

The majority of websites that still maintain separate mobile subdomains inherited this architecture at a time when responsive design was not the standard. Many have migrated to responsive templates but forgot to clean up old mobile URLs or sync the canonicals.

Other cases reveal conflicts between plugins or CMS that automatically generate canonical tags inconsistently across versions. Custom e-commerce platforms are particularly affected, with template management systems that do not communicate with each other.

• Check the consistency of canonicals between mobile and desktop versions across all your strategic pages.
• Audit the alternate media tags from the desktop version to ensure they correctly point to the mobile subdomain.
• Test the display in the SERPs with brand queries to quickly detect any duplication.
• Favor responsive design to avoid this technical complexity if you are launching a new site.
• Document the technical architecture so that any future modifications adhere to this bidirectional canonicalization logic.

Is this statement consistent with real-world observations?

Absolutely. Technical audits regularly reveal this type of duplication, and in 90% of cases, it is indeed a misconfigured or missing canonical issue. What Mueller doesn’t specify is that this duplication can also occur during migrations or redesigns, when old mobile URLs remain indexed for several weeks.

A point rarely addressed: even with perfect canonicals, if your 301 redirects between versions are not synchronous (conditional redirection based on user-agent), Google may temporarily keep both versions in its index. The consolidation timing varies based on how frequently your site is crawled.

What nuances should be added to this advice?

Mueller recommends that the mobile page has a canonical link to the desktop version and vice versa. Let’s be clear: with the widespread adoption of Mobile-First Indexing, this configuration has become partially obsolete for fully responsive sites. If you have only one URL per content piece, the canonical simply points to itself.

The real complexity concerns sites that still maintain a separate mobile subdomain (m.example.com). For these, the rule strictly applies. But be careful: even if configured correctly, this architecture remains fragile. Any template change or CMS update can break these links. [To be checked] regularly via Search Console and automated crawls.

In what instances does this configuration fail?

First common case: canonical conflicts between plugins. If Yoast SEO generates a canonical and a mobile detection plugin generates another, the last declared in the code takes precedence. Google can then receive conflicting signals depending on the crawled version.

Second pitfall: URLs with parameters (utm, tracking, pagination). If your mobile page is m.example.com/page?variant=blue and canonically points to www.example.com/page without the parameter, Google may consider them different contents and maintain the duplication.

What specific actions should be taken to correct this duplication?

First step: audit the current state. Run a search site:m.yoursite.com in Google to see how many mobile pages are indexed. Compare with site:www.yoursite.com. If both return significant results, you have a problem.

Next, check the source code of your key pages. On the mobile version, look for <link rel="canonical">: it should point to the corresponding desktop URL. On the desktop version, look for <link rel="alternate" media="only screen and (max-width: 640px)">: it should point to the mobile version. These two signals must be symmetric and consistent.

What mistakes should be avoided during implementation?

Don't just correct the homepage. Duplication often affects entire sections of the site: product sheets, blog articles, category pages. Automate the generation of these tags through your CMS or templates to ensure consistency at scale.

Another classic mistake: correcting the canonicals but forgetting to update the XML sitemaps. If your mobile sitemap continues to list all the m. URLs as canonicals, Google receives a conflicting signal. Your mobile sitemap should ideally point to the desktop URLs with an alternate mobile attribute or disappear completely if you transition to full responsiveness.

How can it be verified that the correction is effective?

Use Google Search Console to monitor the progress. In the Coverage section, track the gradual decrease of indexed pages on the mobile subdomain. This process takes between 2 and 6 weeks depending on how frequently your site is crawled.

Also test with the URL inspection tool: submit a few key pages of each version and check that Google correctly identifies the desktop version as canonical. If that’s not the case after correction, look for conflicts in your HTTP headers or JavaScript redirects.

• Check canonical tags on a sample of 20-30 strategic pages (desktop and mobile).
• Audit XML sitemaps to remove or correct duplicated mobile URLs.
• Test URL inspection in Search Console to confirm that Google detects the correct canonical version.
• Monitor the change in the number of indexed pages on m. vs www. through weekly site: searches.
• Document the canonical generation rules in your technical documentation to avoid regressions.
• If you maintain a mobile subdomain, plan a migration to a responsive design to simplify the architecture in the medium term.