Google deduplication
Also called: deduplication system, SERP deduplication, duplicate URL clustering
Google deduplication is the set of systems that stop near-duplicate or same-site pages from crowding one query. Google clusters duplicate URLs and shows a single canonical version, caps most sites at two listings ("site diversity"), and drops a page from the regular results once it wins the featured snippet.
Three layers of deduplication
Google deduplicates at more than one point. First, at the index level: when it finds the same or very similar content across multiple URLs, it groups them into a cluster, picks one representative (canonical) URL, and consolidates signals like links onto it. This is not a penalty; the other URLs simply do not get shown.
Second, at the SERP level. The site diversity change (June 6, 2019) means you usually will not see more than two listings from the same site in the top results, though Google may show more when it judges that especially relevant. Subdomains generally count as part of the root domain.
Third, at the feature level. Since January 22, 2020, a page elevated into the featured snippet is no longer repeated in the regular page-1 listings. Google’s Danny Sullivan said it would “no longer repeat the listing in the search results.”
Practical read: two near-identical pages on your site rarely both rank. If you split one intent across thin variants, Google keeps one and drops the rest, and site diversity limits how many of your pages can appear on a single query at all. Consolidating the variants into a single strong URL usually recovers the traffic the duplicates were splitting.
How it affects your traffic
Deduplication is why "more pages on the same topic" often does not turn into more traffic. When two of your URLs compete, Google shows one and the runner-up loses its clicks, and site diversity caps how many of your pages can surface on a single query at all. An SEO consulting engagement audits which pages are cannibalizing each other, consolidates duplicates into one canonical URL, and rebuilds internal links so your strongest page wins the slot instead of splitting it.
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