Definition

Mobile-first indexing means Googlebot primarily crawls and indexes pages with its smartphone agent, treating the mobile version of a site as the canonical content used for ranking.

Google rolled mobile-first indexing out site-by-site from 2018 and applied it as the default for all new sites by 2019; Google has stated it now crawls all sites mobile-first. Content, structured data, and images that exist only on the desktop version are not used for indexing. Sites running separate desktop and mobile URLs (m-dot subdomains) or dynamic-serving setups need to keep both versions in parity, otherwise mobile-only content becomes the source of truth.

Examples

• Hidden mobile content still counts

  A travel site collapses its destination descriptions into accordions on mobile but shows them inline on desktop. Under mobile-first indexing, Google still uses the accordion content for ranking — collapsed text on mobile is treated the same as visible text.

Sources

• Google Search Central — Mobile-first indexing best practices

Related terms

• Indexing
  The process by which a search engine analyses a fetched page and stores information about it so the page can later be returned in search results.
• Core Web Vitals
  A set of three Google metrics that measure real-world page experience: loading speed, interactivity and visual stability.

Where QueryCatch uses this

• SEO Audit
• Page Optimisation