YaCy is a free search engine that anyone can use to build a search portal for their intranet or to help search the public internet. It is an open source peer-to-peer search engine. The strong point of this technology and the aspect that distinguishes YaCy from other search engines is the decentralised nature of YaCy web search.

In order to understand the power of YaCy, you need to distinguish ranking from relevance. While - ranking is technical, relevance is personal. As relevance is personal, relevant search results have different ranks for each person (i.e. order the search results depends on personal needs).

To achieve this, the search must be open and decentralised. The data cannot ever be free or totally relevant if there is censorship, blocking of sites, secret ranking algorithms etc. (not to mention paid adverts). YaCy attempts to provide this free and relevant search through its decentralised model and its capability to handle the complexity of a distributed search index.