Short answer
Google’s official guide names 17 active ranking systems and 4 retired ones. It was last updated on 10 December 2025. Each system does a specific job, from understanding language to limiting how many results one site can show. Knowing which system does what tells you what kind of problem you are looking at after a drop, and which systems cannot be the cause.
Systems and updates are different things
A system runs all the time. An update is a change to one. Google drew that line in November 2022, when it published its guide to ranking systems. A named core update changes the core ranking systems as a whole, while the reviews system, for example, now works continuously. Every confirmed change is on the update tracker.
Understanding what people mean
BERT
An AI system that works out how combinations of words change meaning and intent. There is nothing to optimise for directly; write naturally for people.
RankBrain
Relates words to concepts, so a page can rank without containing every word in the search. Repeating exact keywords adds nothing it needs. Full explanation: RankBrain explained.
Neural matching
Matches the concepts in a search to the concepts in a page. A page that genuinely covers the idea can rank for wording it never uses. Full explanation: neural matching and MUM.
MUM
A model that can understand and generate language. Google says it is not used for general ranking, only for specific tasks such as improving vaccine information and featured snippet callouts. Any claim that MUM demoted your site is wrong. More in neural matching and MUM.
Passage ranking
Identifies individual sections of a page to judge how relevant the page is. Background on its launch is in the passage ranking update. Clear headings and focused sections help long pages answer narrow questions.
Judging quality and trust
Link analysis systems and PageRank
Systems that read how pages link to each other to understand what pages are about and which are most helpful. PageRank has been part of core ranking since Google launched and has changed a great deal since. Links still count. Manipulative links are handled by the spam systems below. Full explanation: what is PageRank, and does Google still use it. Which links count today: do backlinks still matter.
Reviews system
Rewards reviews with insightful analysis and original research, written by experts or enthusiasts who know the subject. It is no longer limited to products. Thin roundups lose ground gradually, not only on update days. Full explanation: Google’s reviews system in 2026.
Original content systems
Show original content, including original reporting, ahead of pages that merely cite it, helped by canonical markup. A real example is in the duplicate content case study. If your work is copied, being clearly the source matters. Full explanation: Google’s original content systems.
Reliable information systems
Several systems that surface authoritative pages, demote low-quality ones and show content advisories when confidence in results is low. These matter most on YMYL topics, where content can affect health, money or safety. Full explanation: reliable information and crisis systems.
Fighting abuse
Spam detection systems
Systems including SpamBrain that deal with content and behaviour breaking Google’s spam policies, updated regularly through spam updates. Every policy is explained in Google spam policies explained.
Removal-based demotion systems
A large volume of valid copyright removals against a site can demote its other content too. Similar signals apply to defamation, counterfeit goods, court orders and exploitative removal practices. A pile of copyright notices can depress a whole site.
Exact match domain system
Words in a domain are one small factor, and this system stops domains built to match a search from getting too much credit. A keyword domain is not a shortcut. Full explanation: the exact match domain system.
Shaping the results page
Deduplication systems
Hide near-identical results. A page shown as a featured snippet is not repeated as a normal listing lower on page one. Losing a blue link after winning a snippet is not a drop. Full explanation: Google’s deduplication systems.
Site diversity system
Generally shows no more than two listings from one site in the top results, and usually treats subdomains as the same site. A third page disappearing is diversity, and moving it to a subdomain rarely helps. Full explanation: Google’s site diversity system.
Freshness systems
Show newer content for searches where people expect it, such as a film just released or a recent earthquake. Full explanation: Google’s freshness systems, and on dates, does changing the date on a post help SEO.
Special situations
Crisis information systems
Show hotlines and trusted organisations for personal crisis searches, and official alerts during disasters. These results sit above ordinary pages for the searches they cover.
Local news systems
Surface local news sources in features such as Top stories and Local news. Local publishers compete in a separate space from national ones.
Retired systems
- Helpful content system: introduced in 2022 and made part of core ranking in March 2024. See helpful content recovery.
- Hummingbird: a major improvement to overall ranking in August 2013. See Hummingbird, RankBrain and BERT.
- Panda: announced in 2011 and part of core ranking from 2015. See the Panda update.
- Penguin: announced in 2012 and part of core ranking from 2016. See the Penguin update.
Retired does not mean gone. Each was absorbed into broader systems that still apply what it did. What replaced each one, and three more that left the list, is covered in retired Google ranking systems.
What the list leaves out
Google calls these its more notable systems, not all of them. NavBoost, described under oath in 2023 as one of Google’s important signals, is not on the list; see do clicks affect Google rankings. Page experience is no longer listed as a system either, although Google still documents Core Web Vitals. Google also now indexes the mobile version of every page, explained in mobile-first indexing explained.
One line in the guide matters most for recovery. Systems work at the page level, but site-wide signals and classifiers also contribute. That is why a sitewide demotion is possible, and also why not every page moves together.
Using this list after a drop
- A page won a snippet and lost its normal listing: deduplication.
- Your third result for a search vanished: site diversity.
- Review pages slid gradually: the reviews system.
- Pages fell sharply during a spam update: spam detection.
- Newer coverage overtook a current topic: freshness.
Anything wider starts with why did my website traffic drop overnight.
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