Stockfish (chess)

Last updated
Stockfish
Developer(s) The Stockfish developers [1]
Initial releaseNovember 2, 2008;15 years ago (2008-11-02)
Stable release
16.1 / February 24, 2024;49 days ago (2024-02-24) [2]
Repository
Written in C++
Operating system Microsoft Windows
macOS
Linux
iOS
Android
Type Chess engine
License GPL-3.0-or-later [3]
Website stockfishchess.org   OOjs UI icon edit-ltr-progressive.svg

Stockfish is a free and open-source chess engine, available for various desktop and mobile platforms. It can be used in chess software through the Universal Chess Interface.

Contents

Stockfish has been one of the best chess engines in the world for several years; [4] [5] [6] it has won all main events of the Top Chess Engine Championship (TCEC) and the Chess.com Computer Chess Championship (CCC) since 2020 and, as of April 2024, is the strongest CPU chess engine in the world with an estimated Elo rating of 3634. [7]

The Stockfish engine was developed by Tord Romstad, Marco Costalba, and Joona Kiiski, and was derived from Glaurung, an open-source engine by Tord Romstad released in 2004. It is now being developed and maintained by the Stockfish community. [8] Stockfish historically used a classical hand-crafted function to evaluate board positions, but as of Stockfish 16.1 (2024) uses an entirely neural network-based evaluation function. [2]

Features

Stockfish can use up to 1024 CPU threads in multiprocessor systems. The maximal size of its transposition table is 32 TB. Stockfish implements an advanced alpha–beta search and uses bitboards. Compared to other engines, it is characterized by its great search depth, due in part to more aggressive pruning and late move reductions. [9] As of February 2024, Stockfish 16 (4-threaded) achieves an Elo rating of 3632 +13
13
on the CCRL 40/15 benchmark. [10]

Stockfish supports Chess960, which is one feature that was inherited from Glaurung. [11] The Syzygy tablebase support, previously available in a fork maintained by Ronald de Man, was integrated into Stockfish in 2014. [12] In 2018 support for the 7-men Syzygy was added, shortly after becoming available. [13]

Stockfish has been a very popular engine on various platforms. On desktop, it is the default chess engine bundled with the Internet Chess Club interface programs BlitzIn and Dasher. On mobile, 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. [14] [15] Stockfish can be compiled to WebAssembly or JavaScript, allowing it to run in the browser. Both chess.com and Lichess provide Stockfish in this form in addition to a server-side program. [16] 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.

Architecture

The Stockfish engine essentially consists of three parts: board representation, heuristic tree search, and board evaluation. Board representation is about coding a chess board state efficiently so that it can be efficiently stored and searched over. Heuristic tree search approximates minimax tree search, which would be too slow to perform. Board evaluation takes in a board representation and gives it a score for how "good" the board is (i.e. the estimated chances of winning). [17]

Starting with Stockfish 12 (2020), a neural network board evaluation function was incorporated. In Stockfish 16.1 (2024), the classical board evaluation functions were removed, leaving just the neural network. [2]

History

The program originated from Glaurung, an open-source chess engine created by Romstad and first released in 2004. Four years later, Costalba, inspired by the strong open-source engine, decided to fork the project. He named it Stockfish because it was "produced in Norway and cooked in Italy" (Romstad is Norwegian, Costalba is Italian). The first version, Stockfish 1.0, was released in November 2008. [18] [19] For a while, new ideas and code changes were transferred between the two programs in both directions, until Romstad decided to discontinue Glaurung in favor of Stockfish, which was the more advanced engine at the time. [20] The last Glaurung version (2.2) was released in December 2008.

Around 2011, Romstad decided to abandon his involvement with Stockfish in order to spend more time on his new iOS chess app. [21] On 18 June 2014 Marco Costalba announced that he had "decided to step down as Stockfish maintainer" and asked that the community create a fork of the current version and continue its development. [22] An official repository, managed by a volunteer group of core Stockfish developers, was created soon after and currently manages the development of the project. [23]

Fishtest

Since 2013, Stockfish has been developed using a distributed testing framework named Fishtest, where volunteers can donate CPU time for testing improvements to the program. [24] [25] [26]

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.

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. [27] In Stockfish 7, Fishtest author Gary Linscott was added to the official list of authors in acknowledgement of his contribution to Stockfish's strength.

As of April 2024, the framework has used a total of more than 12400 years of CPU time to play over 7.2 billion chess games. [28]

NNUE

Stockfish's NNUE visualized Weights-nn-62ef826d1a6d.png
Stockfish's NNUE visualized

In June 2020, an efficiently updatable neural network (NNUE) fork introduced by computer shogi programmers called Stockfish NNUE was discussed by developers. [29] [30] In July 2020 chess news reported that Stockfish NNUE had "broken new ground in computer chess by incorporating a neural network into the already incredibly powerful Stockfish chess engine." [31] A NNUE merge into Stockfish was then announced and development builds became available. [32] [33]

"The NNUE branch maintained by @nodchip has demonstrated strong results and offers great potential, and we will proceed to merge ... This merge will introduce machine learning based coding to the engine, thus enlarging the community of developers, bringing in new skills. We are eager to keep everybody on board, including all developers and users of diverse hardware, aiming to be an inclusive community ...the precise steps needed will become clearer as we proceed, I look forward to working with the community to make this happen!"

Joost VandeVondele, 25 July 2020 [32]

On 2 September 2020, the twelfth version of Stockfish was released, incorporating the aforementioned neural network improvement. According to the blog announcement, this new version "plays significantly stronger than any of its predecessors", typically winning ten times more game pairs than it loses when matched against version eleven. [34] [35]

Competition results

Top Chess Engine Championship

Stockfish is a TCEC multiple-time champion and the current leader in trophy count. Ever since TCEC restarted in 2013, Stockfish has finished first or second in every season except one. In TCEC Season 4 and 5, Stockfish finished runner-up, with Superfinal scores of 23–25 first against Houdini 3 and later against Komodo 1142. Season 5 was notable for the winning Komodo team as they accepted the award posthumously for the program's creator Don Dailey, who succumbed to an illness during the final stage of the event. In his honor, the version of Stockfish that was released shortly after that season was named "Stockfish DD". [36]

On 30 May 2014, Stockfish 170514 (a development version of Stockfish 5 with tablebase support) convincingly won TCEC Season 6, scoring 35.5–28.5 against Komodo 7x in the Superfinal. [37] Stockfish 5 was released the following day. [38] In TCEC Season 7, Stockfish again made the Superfinal, but lost to Komodo with the score of 30.5–33.5. [37] In TCEC Season 8, despite losses on time caused by buggy code, Stockfish nevertheless qualified once more for the Superfinal, but lost the ensuing 100-game match 46.5–53.5 to Komodo. [37] In Season 9, Stockfish defeated Houdini 5 with a score of 54.5 versus 45.5. [37] [39]

Stockfish finished third during season 10 of TCEC, the only season since 2013 in which Stockfish had failed to qualify for the superfinal. It did not lose a game but was still eliminated because it was unable to score enough wins against lower-rated engines. After this technical elimination, Stockfish went on a long winning streak, winning seasons 11 (59 vs. 41 against Houdini 6.03), [37] [40] 12 (60 vs. 40 against Komodo 12.1.1), [37] [41] and 13 (55 vs. 45 against Komodo 2155.00) [37] [42] convincingly. [43] In Season 14, Stockfish faced a new challenger in Leela Chess Zero, but managed to eke out a win by one game (50.5–49.5). [37] [44] Its winning streak was finally ended in season 15, when Leela qualified again and won 53.5–46.5, [37] but Stockfish promptly won season 16, defeating AllieStein 54.5–45.5, after Leela failed to qualify for the superfinal. [37] In season 17, Stockfish faced Leela again in the superfinal, losing 52.5–47.5. However, Stockfish has won every superfinal since: beating Leela 53.5–46.5 in season 18, 54.5–45.5 in season 19, 53–47 in season 20, and 56–44 in season 21. [37] In Season 22, Komodo Dragon beat out Leela to qualify for the superfinal, but was crushed by Stockfish 59.5-40.5. Stockfish did not lose an opening pair in this match. [45] Leela made the superfinal in Seasons 23 and 24, but was crushed by Stockfish both times (58.5-41.5 and 58-42). [46] [47] In Season 25, Stockfish once again defeated Leela, but this time by a narrower margin of 52-48. [48]

Stockfish also took part in the TCEC cup, winning the first edition, but was surprisingly upset by Houdini in the semifinals of the second edition. [37] [49] Stockfish recovered to beat Komodo in the third-place playoff. [37] In the third edition, Stockfish made it to the finals, but was defeated by Leela Chess Zero after blundering in a 7-man endgame tablebase draw. It turned this result around in the fourth edition, defeating Leela in the final 4.5–3.5. [37] In TCEC Cup 6, Stockfish finished third after losing to AllieStein in the semifinals, the first time it had failed to make the finals. Since then, Stockfish has consistently won the tournament, with the exception of the 11th edition which Leela won 8.5-7.5.

Main league
EventYearTime ControlsResultRef
Season 12010100+103rd [50]
Season 22011150+305th [51]
Season 42013150+602nd [52]
Season 52013120+302nd [53]
Season 62014120+301st [54]
Season 72014120+302nd [55]
Season 82015180+302nd [56]
Season 92016180+151st [57]
Season 10201790+102nd [note 1] [58]
Season 112018120+151st [59]
Season 122018120+151st [60]
Season 132018120+151st [61]
Season 142018120+151st [62]
Season 152019120+102nd [63]
Season 162019120+101st [64]
Season 17202090+52nd [65]
Season 18202090+101st [66]
Season 192020120+101st [67]
Season 202020120+101st [68]
Season 212021120+101st [69]
Season 222022120+121st [70]
Season 232022120+121st [71]
Season 242023120+121st [72]
Season 252023120+121st [73]
Cup
EventYearTime ControlsResultRef
Cup 1201830+101st [74]
Cup 2201930+52nd [note 1] [75]
Cup 3201930+52nd [76]
Cup 4201930+51st [77]
Cup 5202030+51st [78]
Cup 6202030+53rd [79]
Cup 7202030+51st [80]
Cup 8202130+51st [81]
Cup 9202130+51st [82]
Cup 10202230+31st [83]
Cup 11202330+32nd [84]
Cup 12202330+31st [85]
Cup 13202430+31st [86]
Fischer random chess (FRC)
EventYearTime ControlsResultRef
FRC 1201930+51st [87]
FRC 2202030+51st [88]
FRC 3202130+52nd [89]
FRC 4202230+51st [90]
FRC 5202230+31st [91]
FRC 6202330+31st [92]
Swiss
EventYearTime ControlsResultRef
Swiss 1202145+72nd [93]
Swiss 2202145+72nd [94]
Swiss 3202245+4.51st [95]
Swiss 4202330+31st [96]
Swiss 5202330+31st [97]
Double fischer random chess (DFRC)
EventYearTime ControlsResultRef
DFRC 1202230+31st [98]
DFRC 2202330+31st [99]
Fischer random double (FRD)
EventYearTime ControlsResultRef
FRD 1202330+31st [100]

Chess.com Computer Chess Championship

Ever since chess.com hosted its first Chess.com Computer Chess Championship in 2018, Stockfish has been the most successful engine. It dominated the earlier championships, winning six consecutive titles before finishing second in CCC7. Since then, its dominance has come under threat from the neural-network engines Leelenstein and Leela Chess Zero, but it has continued to perform well, reaching at least the superfinal in every edition up to CCC11. CCC12 had for the first time a knockout format, with seeding placing CCC11 finalists Stockfish and Leela in the same half. Leela eliminated Stockfish in the semi-finals. However, a post-tournament match against the loser of the final, Leelenstein, saw Stockfish winning in the same format as the main event. After finishing second again to Leela in CCC13, and an uncharacteristic fourth in CCC14, Stockfish went on a long winning streak, taking first place in every championship since.

Main events
EventYearTime ControlsResultRef
CCC201715+21st [101]
CCC 1: Rapid Rumble201815+51st [102]
CCC 2: Blitz Battle20185+21st [103]
CCC 3: Rapid Redux201930+51st [104]
CCC 4: Bullet Brawl20191+21st [105]
CCC 5: Escalation201910+51st [106]
CCC 6: Winter Classic201910+101st [107]
CCC 7: Blitz Bonanza20195+22nd [108]
CCC 8: Deep Dive201915+51st [109]
CCC 9: The Gauntlet20195+2, 10+51st [110]
CCC 10: Double Digits201910+32nd [111]
CCC 11201930+52nd [112]
CCC 12: Bullet Madness!20201+13rd [113]
CCC 13: Heptagonal20205+52nd [114]
CCC 14202015+5, 5+2, 1+14th [115]
CCC Blitz 202020205+51st [116]
CCC Rapid 2021202115+31st [117]
CCC Blitz 202120215+51st [118]
CCC Chess 960 Blitz20215+51st [119]
CCC 16: Rapid202115+31st [120]
CCC 16: Bullet20212+11st [121]
CCC 16: Blitz20225+51st [122]
CCC 17: Rapid202215+31st [123]
CCC 17: Bullet20222+11st [124]
CCC 17: Blitz20225+51st [125]
CCC 18: Rapid202215+31st [126]
CCC 19: Blitz20225+51st [127]
CCC 19: Rapid202215+31st [128]
CCC 19: Bullet20231+11st [129]
CCC 20: Blitz20233+21st [130]
CCC 20: Rapid202310+31st [131]
CCC 20: Bullet20231+11st [132]
CCC 21: Blitz20233+21st [133]
CCC 21: Rapid202310+31st [134]
CCC 21: Bullet20231+11st [135]
CCC 22: Blitz20243+21st [136]
Bonus
EventYearTime ControlsResultRef
CPU Blitz Madness20203+21st [137]
Trillion-Node Throwdown III2020150+51st [138]
No-Castle II20205+21st [139]
Bullet Chess is Fun20202+11st [140]
Checkmate in 420203+21st [141]
Odds Ladder20203+21st [142]
Merry Queen Sac20202+11st [143]
Budapest Bullet20202+12nd [144]
King Gambit Madness20215+51st [145]
Drawkiller Update Party20212+11st [146]
To Castle Or Not To Castle II20213+21st [147]
Eco Mega-Match 2 (part 1)20211+11st [148]
Eco Mega-Match 2 (part 2)20211+11st [149]
Caro-Kann Special20215+21st [150]
King's Indian Defense Special202110+22nd [151]
Dutch Defense Special202110+21st [152]
Evans Gambit Madness202110+22nd [153]
Sicilian Najdorf Special202110+21st [154]
Belgian Stew20212+11st [155]
Saragossa 20212+12nd [156]
Double Bongcloud, Rapid202110+22nd [157]
The Hillbilly Attack 202110+23rd [158]
Romantic Openings: Danish Gambit Accepted 20213+21st [159]
Romantic Openings: Evans Gambit Accepted 20213+21st [160]
Romantic Openings: Urusov Gambit Accepted 20215+21st [161]
Romantic Openings: Blackmar-Diemer Gambit 20215+21st [162]
Romantic Openings: Stafford Gambit 20211+22nd [163]
Romantic Openings: Calabrese Countergambit 20215+21st [164]
Romantic Openings: Traxler Counterattack 20215+22nd [165]
No Black Castling 20225+51st [166]
Draw Killer Bonus202215+51st [167]
Romantic Openings: Wing Gambit 20225+21st [168]
Chess 324 Bonus20225+21st [169]
Classical Cup #1202330+51st [170]
Rating Brawl: Fall 202320231+11st [171]
Classical Cup #2202430+51st [172]

Other matches

Stockfish 5 versus Nakamura

Stockfish's strength relative to the best human chess players was most apparent in a handicap match with grandmaster Hikaru Nakamura (2798-rated) in August 2014. In the first two games of the match, Nakamura had the assistance of an older version of Rybka, and in the next two games, he received White with pawn odds but no assistance. Nakamura was the world's fifth-best human chess player at the time of the match, while Stockfish 5 was denied use of its opening book and endgame tablebase. Stockfish won each half of the match 1.5–0.5. Both of Stockfish's wins arose from positions in which Nakamura, as is typical for his playing style, pressed for a win instead of acquiescing to a draw. [173]

Stockfish 8 versus AlphaZero

In December 2017, Stockfish 8 was used as a benchmark to test Google division DeepMind's AlphaZero, with each engine supported by different hardware. AlphaZero was trained through self-play for a total of nine hours, and reached Stockfish's level after just four. [174] [175] [176] In 100 games from the normal starting position, AlphaZero won 25 games as White, won 3 as Black, and drew the remaining 72, with 0 losses. [177] AlphaZero also played twelve 100-game matches against Stockfish starting from twelve popular openings for a final score of 290 wins, 886 draws and 24 losses, for a point score of 733:467. [178] [note 2]

AlphaZero's victory over Stockfish sparked a flurry of activity in the computer chess community, leading to a new open-source engine aimed at replicating AlphaZero, known as Leela Chess Zero. By January 2019, Leela was able to defeat the version of Stockfish that played AlphaZero (Stockfish 8) in a 100-game match. An updated version of Stockfish narrowly defeated Leela Chess Zero in the superfinal of the 14th TCEC season, 50.5–49.5 (+10 =81 −9), [37] but lost the superfinal of the next season to Leela 53.5–46.5 (+14 =79 -7). [37] [180] The two engines remain very close in strength to each other even as they continue to improve: Leela defeated Stockfish in the superfinal of TCEC Season 17, but Stockfish has won every TCEC season since.

Derivatives

Notes

  1. 1 2 This result takes into account the disqualification of Houdini 6 from TCEC.
  2. The academic paper on this sequence of games does not provide the computer resources allocated to each engine. [179]

Related Research Articles

<span class="mw-page-title-main">Computer chess</span> Computer hardware and software capable of playing chess

Computer chess includes both hardware and software capable of playing chess. Computer chess provides opportunities for players to practice even in the absence of human opponents, and also provides opportunities for analysis, entertainment and training. Computer chess applications that play at the level of a chess grandmaster or higher are available on hardware from supercomputers to smart phones. Standalone chess-playing machines are also available. Stockfish, Leela Chess Zero, GNU Chess, Fruit, and other free open source applications are available for various platforms.

<span class="mw-page-title-main">Evaluation function</span> Function in a computer game-playing program that evaluates a game position

An evaluation function, also known as a heuristic evaluation function or static evaluation function, is a function used by game-playing computer programs to estimate the value or goodness of a position in a game tree. Most of the time, the value is either a real number or a quantized integer, often in nths of the value of a playing piece such as a stone in go or a pawn in chess, where n may be tenths, hundredths or other convenient fraction, but sometimes, the value is an array of three values in the unit interval, representing the win, draw, and loss percentages of the position.

<span class="mw-page-title-main">Chess engine</span> Computer program for chess analysis and game

In computer chess, a chess engine is a computer program that analyzes chess or chess variant positions, and generates a move or list of moves that it regards as strongest.

<span class="mw-page-title-main">Houdini (chess)</span> UCI chess engine

Houdini is a UCI chess engine developed by Belgian programmer Robert Houdart. It is influenced by open-source engines IPPOLIT/RobboLito, Stockfish, and Crafty. Versions up to 1.5a are available for non-commercial use, while 2.0 and later are commercial only.

<span class="mw-page-title-main">Komodo (chess)</span> UCI Chess Engine

Komodo and Dragon by Komodo Chess are UCI chess engines developed by Komodo Chess, which is a part of Chess.com. The engines were originally authored by Don Dailey and GM Larry Kaufman. Dragon is a commercial chess engine, but Komodo is free for non-commercial use. Dragon is consistently ranked near the top of most major chess engine rating lists, along with Stockfish and Leela Chess Zero.

Top Chess Engine Championship, formerly known as Thoresen Chess Engines Competition, is a computer chess tournament that has been run since 2010. It was organized, directed, and hosted by Martin Thoresen until the end of Season 6; from Season 7 onward it has been organized by Chessdom. It is often regarded as the Unofficial World Computer Chess Championship because of its strong participant line-up and long time-control matches on high-end hardware, giving rise to very high-class chess. The tournament has attracted nearly all the top engines compared to the World Computer Chess Championship.

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Don Dailey was an American researcher in computer chess and a game programmer. Along with collaborator Larry Kaufman, he was the author of the chess engine Komodo. Dailey started chess programming in the 1980s, and was the author and co-author of multiple commercial as well as academic chess programs. He has been an active poster in computer chess forums and computer Go newsgroups. He was raised as a Jehovah's Witness and served in recent years as an elder in the church of Roanoke.

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<span class="mw-page-title-main">Leela Chess Zero</span> Deep neural network-based chess engine

Leela Chess Zero is a free, open-source, and deep neural network–based chess engine and volunteer computing project. Development has been spearheaded by programmer Gary Linscott, who is also a developer for the Stockfish chess engine. Leela Chess Zero was adapted from the Leela Zero Go engine, which in turn was based on Google's AlphaGo Zero project. One of the purposes of Leela Chess Zero was to verify the methods in the AlphaZero paper as applied to the game of chess.

The 14th season of the Top Chess Engine Championship took place between 17 November 2018 and 24 February 2019. Stockfish was the defending champion, having defeated Komodo in the previous season's superfinal.

The 15th season of the Top Chess Engine Championship began on the 6 March 2019 and ended on 12 May 2019.

The 16th season of the Top Chess Engine Championship began on 15 July 2019 and ended on 13 Oct 2019.

The 17th season of the Top Chess Engine Championship began on 2 January 2020 and ended on 22 April 2020. TCEC Season 16 3rd-place finisher Leela Chess Zero won the championship, defeating the defending champion Stockfish 52.5-47.5 in the superfinal.

The 18th season of the Top Chess Engine Championship began on 4 May 2020 and ended on 3 July 2020. The defending champion was Leela Chess Zero, which defeated Stockfish in the previous season's superfinal. The two season 17 superfinalists qualified again for the superfinal. This time Stockfish won, winning by 7 games (+23−16=61).

<span class="mw-page-title-main">Efficiently updatable neural network</span> Neural network based evaluation function

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The 19th season of the Top Chess Engine Championship began on 6 August 2020 and ended on 16 October 2020. The season 19 superfinal was a rematch between Stockfish and Leela Chess Zero, the same two engines that had contested the superfinal in the previous two seasons. Stockfish, the defending champion, won by 9 games.

The 20th season of the Top Chess Engine Championship began on 1 December 2020 and ended on 1 February 2021. The defending champion was Stockfish, which defeated Leela Chess Zero in the previous season's superfinal. The season 20 superfinal was a rematch between the same two engines. Stockfish once again came out ahead, winning by 6 games.

Yuri Semyonovich Gusev is a Soviet chess player and was a Merited Master of Sport of the USSR (1951). He is also a former radio engineer. Gusev peaked with a classical Elo rating of 2380, making him the equivalent of a FIDE Master in terms of strength, although it is not clear what title he ultimately achieved. As of December 2022, it is unknown if he is still alive.

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Further reading