Mobile-First Indexing

Mobile-first indexing is Google's practice of using the mobile version of a page, crawled with the Googlebot Smartphone user agent, as the version it indexes and ranks. If content, links or structured data exist only on the desktop version, Google generally does not see them.

The shift took years. Google began mobile-first crawling in 2016, announced on October 31, 2023 that the move was complete for almost all sites, and said that after July 5, 2024 it would crawl the remaining desktop-only sites with Googlebot Smartphone as well. Sites whose content cannot be accessed on a mobile device at all are no longer indexable. Googlebot Desktop still appears in logs for a few features, such as product listings and Google for Jobs.

Google's mobile-first indexing best practices come down to parity between versions:

• The same primary content on mobile as on desktop, using tabs or accordions to save space rather than removing text
• The same robots meta tags, since a noindex on mobile removes the page
• The same structured data, titles and meta descriptions
• Images and videos with the same alt text, captions and stable URLs
• No primary content that loads only after a tap, swipe or typing, because Googlebot does not interact with the page

Google recommends responsive design, which serves the same HTML at the same URL to every device and avoids most parity problems. Dynamic serving and separate m-dot URLs still work but need careful checking.

Mobile-first indexing now also decides eligibility for Google's AI features. Google's guidance says a page must be indexed and eligible to show with a snippet to appear as a supporting link in AI Overviews or AI Mode, with no extra technical requirements. Because the index is built from the mobile version, anything missing from mobile is missing from the pool those features retrieve from.

Other AI crawlers work differently. GPTBot, OAI-SearchBot, ClaudeBot and PerplexityBot use their own user agents rather than a smartphone profile, and a December 2024 Vercel and MERJ study found that none of the major AI crawlers it measured executed JavaScript, while Google's crawlers (which also serve Gemini) render it fully. For a responsive site this matters less, since every crawler receives the same HTML. For sites using dynamic serving, it is worth checking what HTML each AI user agent actually receives, and for sites that render content client-side, server-side rendering is the safer choice for both mobile-first indexing and AI crawlers. Our free AI crawler URL inspector shows what a page looks like to them, and JavaScript rendering covers the underlying issue.

Performance is measured on mobile too. Core Web Vitals thresholds were unchanged as of October 2026: Largest Contentful Paint at 2.5 seconds or less, Interaction to Next Paint (which replaced First Input Delay in March 2024) at 200 milliseconds or less, and Cumulative Layout Shift at 0.1 or less, each at the 75th percentile of page loads. In October 2026 Chrome added experimental versions of all three to CrUX that also count soft navigations in single-page apps, with a target of leaving experimental status in May 2027. Use the URL Inspection tool in Search Console to see the rendered mobile page Google indexed, and server logs to confirm which crawlers fetch it.