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Mobile vs Desktop Diff

What it does

The Mobile vs Desktop Diff fetches a URL twice — once with a desktop user-agent, once with a mobile user-agent — and compares the responses. The output shows differences in status code, final URL, title, description, H1, link count, image count, body size, and word count. Significant differences (different titles, different content, different URLs) flag as potential cloaking; minor differences (slightly different link counts) flag as informational.

Common situations

You suspect a site might be serving different content to mobile crawlers than to desktop users (cloaking). Run the diff — if mobile and desktop responses differ significantly in title, description, or content body, you have evidence. Cloaking is a Google policy violation and a long-term ranking risk.

A site has a separate mobile subdomain (m.example.com) and you want to verify the canonical URL is consistent across user-agents. Sometimes desktop URLs canonicalise to www; mobile redirects to m.; the result is two parallel URL structures. The diff surfaces this immediately.

A page is being mobile-first indexed by Google but ranks well only on desktop. The mobile version is likely missing content or returning differently. The diff shows what mobile crawlers actually receive — usually a stripped-down version, or a JavaScript-only render that bots don’t fully process.

You are migrating from a desktop-and-mobile-separate setup to a responsive one. Verify post-migration that mobile and desktop now serve the same content. The diff confirms the consolidation.

You are auditing a competitor whose mobile rankings are higher than their desktop. Their mobile experience may be substantively different (faster, more focused content, simpler layout). The diff surfaces the structural differences in what’s served.

What you need to know

Google has been mobile-first indexing since 2019 — the version of the page Googlebot crawls with a mobile user-agent is what gets indexed. Desktop is now treated as the secondary view. This means: the content that ranks is the mobile content. If mobile and desktop differ in meaningful ways, mobile is what Google cares about.

The diff compares nine fields:

Status: HTTP response code. Mobile and desktop should return the same status. A redirect on mobile but not desktop (or vice versa) is significant.

Final URL: where redirects land. Should be identical. A separate mobile URL structure (m.example.com vs www.example.com) is the historical pattern but largely deprecated; Google prefers responsive design with one URL.

Title: the <title> tag. Should be identical or very similar. Different titles per user-agent is a strong cloaking signal.

Description: the meta description. Should be identical.

H1: the page’s main heading. Should be identical.

Word count: the rendered text content. Some difference is expected (mobile sometimes hides supplementary content), but a 50%+ difference is concerning.

Link count: number of <a> tags. Mobile sometimes has fewer (compact navigation, hidden footer links) but should be roughly comparable.

Image count: number of <img> tags. Mobile often has fewer (hidden hero images, simplified visuals), but the body content images should match.

Body size: the HTML response size in bytes. A large mobile/desktop gap suggests genuinely different content.

The diff reports differences as either “significant” (status, final URL, title, description, H1) or “informational” (counts and sizes). Significant differences need investigation; informational differences are normal in most responsive layouts.

What the diff does NOT do: render JavaScript. The diff compares server-returned HTML for both user-agents. Sites that differentiate via JavaScript (showing different content based on viewport in client code) appear identical to the diff because the server response is the same. Cloaking is typically server-side, so this is the relevant test for cloaking detection.

Frequently asked questions

What is cloaking?

Serving different content to crawlers than to users. Common patterns: keyword-stuffed text shown to bots and hidden from users; redirects that affect users but not bots; or substantively different page versions per user-agent. Google’s policy violations include any deliberate divergence between bot and user views.

Is responsive design “cloaking”?

No — responsive design uses CSS to adapt the same HTML to different viewports. The HTML returned to mobile and desktop user-agents is identical; only the rendering differs. This is what Google explicitly recommends.

What about separate mobile sites (m.example.com)?

Allowed but discouraged. If you have a separate mobile site, the mobile and desktop versions should reference each other with rel="alternate" and the canonical should be the desktop URL. Most modern best practice is to consolidate to a single responsive URL.

Does this catch all cloaking?

No. Cloaking can also be done via IP-based detection (showing one thing to known Googlebot IPs, another to user IPs) which the tool can’t detect from a single fetch. For deeper investigation, fetch from multiple IP ranges or use Google’s URL Inspection tool which fetches with a real Googlebot.

Why might mobile and desktop legitimately differ?

Truly responsive sites should be identical at the HTML level. Differences usually come from:

  • Server-side mobile/desktop branching (showing different content based on UA detection — usually a legacy pattern)
  • A/B tests routing different user-agents to different variants
  • AdTech or analytics platforms returning different scripts based on UA
    None of these are cloaking per se, but they all reduce the consistency Google expects.

What user-agent strings does the tool use?

Desktop: a recent Chrome desktop UA. Mobile: a recent Chrome mobile UA. Both identify themselves as BeaconSEO/1.0 so site owners can recognise the tool’s traffic if they choose.

Are JavaScript-rendered differences detected?

No — the diff compares server-returned HTML before JavaScript executes. Sites that render different content per user-agent via client-side JavaScript appear identical to the diff. For JavaScript-driven differences, use a headless browser tool.

What’s an acceptable level of difference?

Title, description, H1: identical. Final URL and status: identical. Link count, image count, word count: within ~10-15%. Larger gaps need investigation.

Common problems

Problem: Mobile and desktop have different final URLs.

The site is likely on a separate-mobile-URL pattern (m. subdomain or /mobile/ path). Modern best practice is responsive design with one URL. Migration to consolidated URLs is a non-trivial project but improves SEO consistency.

Problem: Word count differs by 30% between mobile and desktop.

The mobile version is hiding or excluding content. Sometimes intentional (mobile-only summary view); sometimes accidental (CSS hiding content that should be rendered). Verify by viewing both versions in browser dev tools — what should mobile users actually see?

Problem: Title is different between mobile and desktop.

Almost certainly an accidental cloaking situation — maybe the CMS has separate “mobile title” and “desktop title” fields and someone filled them in differently. Should be identical. Update the CMS so one title is used regardless of UA.

Problem: Mobile gets a 200 but desktop gets a 301.

A redirect rule is targeting one user-agent and not the other. Usually a CDN rule or security plugin behaving inconsistently. Check redirect logic at every layer (origin, application, CDN, security).

Problem: Diff shows identical content but Google’s URL Inspection shows different rendering.

Google renders JavaScript before indexing. The diff doesn’t. If JavaScript runs differently per user-agent, real Google sees the difference; the diff doesn’t. Use Google’s URL Inspection tool for JavaScript-aware testing.

Tips

  • Run the diff after any change to UA-detection logic, CDN rules, or mobile-specific configuration. Drift is silent until checked.
  • Significant differences in title, description, H1, status, or final URL need investigation. Informational differences in counts are usually fine.
  • Mobile-first indexing means the mobile version is what ranks. If mobile is the weaker version, that’s the version to fix.
  • Don’t conflate responsive (CSS-driven) differences with cloaking (HTML-driven). Responsive is fine; cloaking is a violation.
  • Use Google’s URL Inspection tool alongside this diff. Inspection uses real Googlebot rendering; the diff is a fast first-pass check.

Related tools in this suite

The Page SEO Audit audits a single user-agent view; the diff complements it by showing how that view differs across user-agents. The Mobile-Friendly Test goes further on the mobile side specifically — viewport, scaling, text sizes.

What this looks like at scale

For a single site, the diff is fine. For a content set, mobile-and-desktop consistency should be a deploy-time check: every release runs the diff against representative URLs and flags any significant divergence. The WP Beacon Plugin audits mobile and desktop versions consistently across every page on every visit.

Take it further

If a site has structural mobile-vs-desktop divergence (separate mobile site, m. subdomain, server-side UA branching), the consolidation work is a discrete migration project. Start a conversation about what the consolidation looks like.