Why does Google offer two crawlers in the URL Inspection Tool?

What are the differences between the two crawlers offered?

The URL Inspection Tool from the Search Console allows you to test the rendering of a page through two distinct user-agents: Googlebot Desktop and Googlebot Smartphone. Each simulates how Google crawls and indexes your content based on the type of device.

The mobile crawler uses a smartphone viewport and interprets HTML, CSS, and JavaScript just like a modern mobile browser would. The desktop crawler behaves like a traditional browser with a wide screen. This distinction is not cosmetic; it determines which content Google will actually index and rank.

Why is the mobile version becoming prioritized?

Mobile-first indexing means that Google now uses the mobile version of a page for indexing and ranking, even for searches conducted on desktop. This is a complete paradigm shift from the time when the desktop version served as the reference.

If your site provides different content between mobile and desktop — such as a simplified HTML structure, truncated text, or improperly lazy-loaded images — it is the mobile version that will dominate. Content missing from the mobile version risks not being indexed at all, even if it appears on desktop.

How should you interpret the results from the two crawlers?

When you launch a URL inspection, Google displays the HTML rendering, blocked resources, JavaScript errors, and indexing status for each user-agent. Discrepancies between the two versions often reveal critical issues.

For instance, if the mobile crawler detects blocked or poorly rendered content while the desktop version has no issues, you know exactly where to investigate. Differences in the final DOM, canonical tags, or internal linking may explain unexplained performance gaps.

• Mobile crawler: determines effective indexing and ranking since mobile-first indexing
• Desktop crawler: remains useful for diagnosing inconsistencies between versions but no longer takes precedence
• JavaScript rendering: both crawlers execute JS, but timeouts and available resources may differ
• Differentiated content: any element present on desktop but absent on mobile risks not being indexed
• Structured data: must be identical on both versions to avoid inconsistencies

Does this statement align with observed practices?

Yes, completely. The evidence confirms that Google now prioritizes indexing and ranking from the mobile version. SEO audits regularly show sites losing positions because their mobile content is lacking compared to desktop.

A typical case: an e-commerce site that hides long product descriptions behind accordions on mobile, or that removes text blocks to 'lighten' the experience. Result: Google no longer sees this content, even for desktop queries. Positions drop, and teams scramble for explanations elsewhere.

What nuances need to be added to this statement?

Google says that information from the mobile crawler will become more significant, but that has already been the case for several years. Mobile-first indexing is deployed on almost all sites. Saying 'will become' when referring to a change that has already been established reflects typical Google communication: cautious, even when the switch has been made.

Another point: the inspection tool only shows a simulation of the crawl. The actual rendering during a Googlebot pass can vary based on network conditions, server load, or JavaScript timeouts. Never take the URL Inspection Tool as gospel; cross-check with server logs and coverage data in the Search Console.

In what cases does this rule not fully apply?

Sites that do not have a dedicated mobile version — those using well-designed responsive design with the same HTML for all devices — only have one rendering to check. In this case, both crawlers should yield nearly identical results. If they do not, it is often a CSS or improperly configured viewport issue.

Moreover, certain types of content — particularly complex B2B sites, and SaaS platforms with heavy dashboards — may legitimately provide an enriched desktop experience. However, even in this case, the mobile version must include the essential indexable content: text, titles, links, structured data. Otherwise, you are working against yourself. [To verify]: Google has never published specific thresholds on the percentage of acceptable content missing on mobile.

What should you prioritize checking in the URL Inspection Tool?

Start by inspecting your strategic pages (landing pages, product sheets, pillar articles) in mobile mode first. Then compare with the desktop version. The gap reveals your weaknesses.

Ensure that the text content, Hn tags, internal links, and structured data are identical. If the mobile version hides text in accordions, make sure it remains in the DOM and accessible to the crawler. Inspect the final HTML rendering: this is what Google indexes, not your original source code.

What errors should be absolutely avoided?

Never block critical CSS or JavaScript resources via robots.txt on mobile. Google needs to execute JS to generate the final rendering. Blocked CSS can hide content that Google will never see.

Avoid dynamic content loaded too late as well. If your lazy loading triggers important text to appear after several seconds of scrolling, Googlebot may never see it. JS execution timeouts are limited, even if Google does not provide precise figures. [To verify]: exact delays vary depending on server load and page priority.

How do you correct discrepancies detected between mobile and desktop?

If you are using a separate mobile site (m.example.com), align the content with the desktop version. If you are responsive, track display:none or visibility:hidden applied on mobile that hides indexable content.

For complex sites needing fine adjustments — managing accordions, optimized lazy loading, critical JavaScript rendering — it may be wise to consult a specialized SEO agency. These optimizations often involve front-end code and require precise technical support to avoid missteps.

• Inspect strategic pages through both crawlers (mobile first)
• Compare final HTML rendering between mobile and desktop
• Verify that text content, Hn tags, and linking are identical
• Check that critical CSS/JS resources are not blocked on mobile
• Test lazy loading to ensure content appears in the initial rendering
• Validate that structured data is present on both versions