Stockfish – An Open Source Chess Game Engine

Stockfish is an open source game engine and one of the best CPU chess engines in the world. It is free and Universal Chess Interface (UCI) compliant, distributed under under the GNU General Public License version 3 (GPL v3). It is a fork of Glaurung engine, which is an open-source engine, developed by Tord Romstad and released in fall 2004. Glaurung was written in C and later versions were completely written in C++. The authors of this game engine are Tord Romstad, Marco Costalba, Joona Kiiski and Gary Linscott.

Currently Stockfish version 14 is available which incorporates new efficiently updatable neural network backwards (NNUE) architecture and is much stronger than previous versions. The NNUE evaluation is first introduced in shogi (Japanese form of chess), and ported to Stockfish subsequently. Stockfish combines the brute-force computing approach of traditional Stockfish with the advanced evaluation capabilities of NNUE chess and can look at more than 50,000,000 positions per second

It can run on Windows, macOS, Android, iOS and Linux. It can also be compiled to WebAssembly or JavaScript, to run in web browsers.

Stockfish utilizes distributed testing framework named Fishtest, where volunteers can donate CPU time for testing improvements to the program. This helped the game engine to gain a growth of 120 Elo points and gain the highest rating in 2014.

Features of Stockfish

Board Representation: 8×8 Board, Bitboards with Little-Endian Rank-File Mapping (LERF), Magic Bitboards and BMI2 – PEXT Bitboards, Piece-Lists until Stockfish
Search: Iterative Deepening, Aspiration Windows and Quiescence Search
Evaluation: Efficiently updatable neural network (NNUE)

Stockfish filed a lawsuit against ChessBase as it hides from their customers Stockfish as the true origin of key parts of the Fat Fritz 2 chess engine. Due to Chessbase’s repeated license violations, leading developers of Stockfish have terminated their GPL license with ChessBase permanently.