YaCy is the peer-to-peer search engine created by Michael Christen.
Michael Christen announced development of YaCy in 2003 as a search engine based on peer-to-peer networking. Unlike a conventional centralized search engine, YaCy is designed around independent peers that can crawl websites, analyze pages, build local indexes, and share indexing information across a network.
The project’s decentralized architecture means that no single central server has to control the entire index. Users can run YaCy locally, use it as a private search tool, or participate in a shared search network. Its software is open source and written in Java, and the project is distributed under the GNU General Public License.
YaCy’s name is pronounced “ya see.” The system can operate in different ways, including crawling the wider web or indexing pages encountered through a local proxy. This privacy-oriented model is why YaCy is often grouped with distributed or decentralized search engines rather than mainstream centralized services such as Google or Bing.
Mojeek and Gigablast are separate search engines, while Searx is primarily a metasearch tool.