Mobile-First Indexing
In one line
Mobile-first indexing is Google's policy of using the mobile version of a page as the primary basis for indexing and ranking.
Going deeper
Mobile-first indexing became the default for new sites in 2019, and Google announced the rollout was effectively complete on October 31, 2023. Anything visible on desktop but hidden on mobile is effectively invisible to Google.
The practical check is simple: confirm that the mobile version exposes the same body content, metadata, structured data and images as desktop. Responsive sites tend to be fine; separate m. domains demand more care.
Core Web Vitals are also evaluated on mobile, so it makes sense to optimise mobile performance first and let desktop benefit from the same work.
Sources
Related terms
Indexing
Indexing is the step where a search engine stores a crawled page in its database. If a page is not indexed, it cannot appear in search results at all.
SEOPageSpeed Insights
PageSpeed Insights (PSI) is Google's free tool that scores a page's performance on mobile and desktop, using Core Web Vitals and offering concrete optimization tips.
SEOCrawlability
Crawlability is how easily a search engine bot can reach and follow your site's pages — the precondition for indexing.
SEOGoogle Search Console
Google Search Console (GSC) is Google's free tool for monitoring how a site performs in Search — impressions, clicks, indexing status and technical issues.
SEOStructured Data
Structured data is content marked up in a standard format so search engines and AI systems can understand exactly what each part of the page means.
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