About Search Engine Basics
A technical reference library on how search engines work, written to be read at length and cited, not to sell anything.
What this site is
Search Engine Basics explains the mechanism of web search: how a crawler finds and fetches pages, how those pages become records in an index, how a query is interpreted, and how results are retrieved and ordered. It is written for two readers at once — someone who wants to understand how the thing works, and a developer who wants the code and the data structures.
The site is organised as thirteen guides, each a full explanation of one stage or topic, with articles underneath them going into specific problems. There is also a glossary, because a large amount of confusion in this subject comes from two different things being called by the same name.
Why it exists
Most writing about how search works falls into one of two categories. It is either marketing produced by a company selling a tool, or it is a summary of another summary, where a claim someone inferred in 2014 has been repeated so often that it now reads as documentation.
This site is written the other way round. Claims come from search engines' own documentation, from published standards and papers, or from experiments run on sites we control and can measure. Where something is genuinely unknown — and a great deal about ranking is genuinely unknown — the page says so rather than filling the gap with a confident guess.
Who writes it
Everything is written by a named person with their working history attached, and the authors page lists who they are. The editorial process, including how sources are graded and when a page's modified date changes, is set out in the editorial policy. Original experiments follow the method described in how we test.
How it is funded
The site is currently funded by its owner rather than by advertising or sponsorship. If that changes — display advertising, affiliate links, or a sponsored placement of any kind — it will be disclosed here and labelled on the pages it affects, before it goes live rather than after. No source, tool or company mentioned on this site has paid to be mentioned.
Corrections
Corrections are published on the page they affect, and the modified date changes when they are. If something here is wrong, tell us — ideally with the primary source that shows it. Being corrected in public is a reasonable price for asking to be treated as a source.