Search algorithm
What is a search algorithm?
A search algorithm is the collection of rules and machine-learning systems a search engine uses to choose which pages to show for a query and in what order. It weighs many signals, such as relevance to the words searched, content quality, links, freshness, location and page experience, to rank results.
Google’s “algorithm” is really many systems working together. Google documents several in its guide to ranking systems, including PageRank (links), BERT and neural matching (understanding language), the reviews system, freshness systems, deduplication, and SpamBrain for spam detection. Since March 2024 the signals from the former helpful content system are part of the core ranking systems.
Google changes these systems constantly, with thousands of small changes a year and a few broad core updates. The exact weighting of signals isn’t public.
In broad terms, the algorithm first works out what the query means, including spelling, synonyms and the likely search intent. It then finds indexed pages that could be relevant, assesses their quality and usefulness, and considers context such as the searcher’s location, language and device. The final results page can mix web pages with images, videos, local results and AI-generated answers, each chosen by its own systems.
Why search algorithm matters for SEO
Everything in SEO is an attempt to match what the algorithm rewards. You don’t need its source code: Google states plainly that it aims to reward helpful, reliable, people-first content, and most lasting SEO work follows from that.
Understanding that the algorithm is a set of systems also explains odd behaviour, such as a page ranking well for one query and badly for a near-identical one.
Is Google updating right now? Every confirmed core and spam update, with rollout dates and daily ranking volatility, is on the OpenSEO Google algorithm update tracker.
Search algorithm FAQ
How often does Google change its algorithm?
Constantly. Google makes thousands of changes a year, most too small to notice, and announces larger ones such as core and spam updates on its Search Status Dashboard.
Is the Google algorithm public?
No. Google publishes guidance and describes its main ranking systems, but not the code or the weights it gives to each signal.
Related SEO terms
Ranking factors are the signals search engines use to decide how high a page appears, such as relevance, content quality, links and page experience.
A Google algorithm update is a change to how Google ranks results. Big ones, like core and spam updates, are announced and can move rankings sharply.
A Google core update is a broad change to Google’s main ranking systems, released several times a year, that can move rankings for many sites.
PageRank is Google’s original algorithm for scoring pages by the number and quality of links pointing to them. Google still uses a version of it.
SpamBrain is Google’s AI-based spam prevention system, used to detect spam content and link spam in search results.
Helpful content is Google’s term for people-first content made to help readers, not to rank. Since 2024 it is assessed by Google’s core systems.