Stockfish is a free and open-source Universal Chess Interface chess engine, available for various desktop and mobile platforms. It is developed by Marco Costalba, Joona Kiiski, Gary Linscott, Stéphane Nicolet, and Tord Romstad, with many contributions from a community of open-source developers.

Stockfish is consistently ranked first or near the top of most chess-engine rating lists and is the strongest open-source conventional chess engine in the world. It won the unofficial world computer chess championships in seasons 6 (2014), 9 (2016), 11 (2018), 12 (2018), 13 (2018), 14 (2019), and 16 (2019). It finished runner-up in season 5 (2013), 7 (2014), 8 (2015), and 15 (2019).

Stockfish is derived from Glaurung, an open-source engine by Romstad released in 2004. 

Fishtest

Since 2013, Stockfish has been developed using a distributed testing framework named Fishtest, where volunteers are able to donate CPU time for testing improvements to the program.

Changes to game-playing code are accepted or rejected based on results of playing of tens of thousands of games on the framework against an older "reference" version of the program, using sequential probability ratio testing. Tests on the framework are verified using the chi-squared test, and only if the results are statistically significant are they deemed reliable and used to revise the software code.

As of June 2018, the framework has used a total of more than 1200 years of CPU time to play more than 840 million chess games.After the inception of Fishtest, Stockfish experienced an explosive growth of 120 Elo points in just 12 months, propelling it to the top of all major rating lists.In Stockfish 7, FishTest author Gary Linscott was added to the official list of authors in acknowledgement of his contribution to Stockfish's strength.

Platforms

Release versions and development versions are available as C++ source code and as precompiled versions for Microsoft Windows, macOS, Linux 32-bit/64-bit and Android.

Stockfish has been a very popular engine for various platforms. On the desktop, it is the default chess engine bundled with the Internet Chess Club interface programs BlitzIn and Dasher. On the mobile platform, it has been bundled with the Stockfish app, SmallFish and Droidfish. Other Stockfish-compatible graphical user interfaces (GUIs) include Fritz, Arena, Stockfish for Mac, and PyChess.As of March 2014, Stockfish is the chess engine used by Lichess, a popular online chess site.

Specifications

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