Package: pyffish
Fairy-StockfishOverviewFairy-Stockfish is a chess variant engine derived fromStockfishdesigned for the support of fairy chess variants and easy extensibility with more games. It can play various regional, historical, and modern chess variants as well asgames with user-defined rules. Forcompatibility with graphical user interfacesit supports the UCI, UCCI, USI, UCI-cyclone, and CECP/XBoard protocols.The goal of the project is to create an engine supporting a large variety of chess-like games, equipped with the powerful search of Stockfish. Despite its generality theplaying strengthis on a very high level in almost all supported variants. Due to its multi-protocol support Fairy-Stockfish works with almost any chess variant GUI.InstallationYou can download theWindows executableorLinux binaryfrom thelatest releaseorcompile the program from source. The program comes without a graphical user interface, so you perhaps want to use it together with acompatible GUI, orplay against it onlineatpychess,lishogi, orlichess. Read more abouthow to useFairy-Stockfish in the wiki.If you want to preview the functionality of Fairy-Stockfish before downloading, you can try it out on theFairy-Stockfish playgroundin the browser.Optional NNUE evaluation parameter files to improve playing strength for many variants are in thelist of NNUE networks.
For the regional variants Xiangqi, Janggi, and Makrukdedicated releases with built-in NNUE networksare available. See thewikifor more details on NNUE.ContributingIf you like this project, please support its development viapatreonorpaypal, bycontributing CPU timeto the framework for testing of code improvements, or bycontributing to the codeor documentation. Anintroduction to the code basecan be found in the wiki.Supported gamesThe games currently supported besides chess are listed below. Fairy-Stockfish can also play user-defined variants loaded via a variant configuration file, see the filesrc/variants.iniand thewiki.Regional and historical gamesXiangqi,Manchu,Minixiangqi,Supply chessShogi,Shogi variantsJanggiMakruk,ASEAN, Makpong, Ai-WokOuk Chatrang,Kar OukSittuyinShatar,Jeson MorShatranj,CourierRaazuvaaChess variantsCapablanca,Janus,Modern,Chancellor,Embassy,Gothic,Capablanca random chessGrand,Shako,Centaur,Tencubed,OpulentChess960,Placement/Pre-ChessCrazyhouse,Loop,Chessgi,Pocket Knight, Capablanca-CrazyhouseBughouse,KoedemSeirawan, Seirawan-Crazyhouse,Dragon ChessAmazon,Chigorin,Almost chessHoppel-Poppel, New ZealandAntichess,Giveaway,Suicide,Losers,CodrusExtinction,Kinglet, Three Kings,CoregalKing of the Hill,Racing KingsThree-check, Five-checkLos Alamos,Gardner's MinichessAtomicHorde,Maharajah and the SepoysKnightmate,Nightrider,GrasshopperDuck chess,Omicron,Gustav IIIBerolina Chess,Pawn-Sideways,Pawn-Back,Torpedo,Legan ChessSpartan ChessWolf ChessTroitzky ChessShogi variantsMinishogi,EuroShogi,Judkins shogiKyoto shogi,MicroshogiDobutsu shogi,Goro goro shogiTori shogiYari shogiOkisaki shogiSho shogiRelated gamesAmazonsAtaxxBreakthroughClobberCfour,Tic-tac-toeFive Field KonoFlipersi,FlipelloFox and HoundsIsolationJoustSnailtrailHelpSee theFairy-Stockfish Wikifor more info, or if the required information is not available, open anissueor join ourdiscord server.BindingsBesides the C++ engine, this project also includes bindings for other programming languages in order to be able to use it as a library for chess variants. They support move, SAN, and FEN generation, as well as checking of game end conditions for all variants supported by Fairy-Stockfish. Since the bindings are using the C++ code, they are very performant compared to libraries directly written in the respective target language.PythonThe python bindingpyffishcontributed by@gbtamiis implemented inpyffish.cpp. It is e.g. used in the backend for thepychess server.JavascriptThe javascript bindingffish.jscontributed by@QueensGambitis implemented inffishjs.cpp. The compilation/binding to javascript is done using emscripten, see thereadme.PortsWebAssemblyFor in-browser use aport of Fairy-Stockfish to WebAssemblyis available atnpm. It is e.g. used for local analysis onpychess.org. Also see theFairy-Stockfish WASM demoavailable athttps://fairy-stockfish-nnue-wasm.vercel.app/.StockfishOverviewStockfishis a free, powerful UCI chess engine
derived from Glaurung 2.1. Stockfish is not a complete chess program and requires a
UCI-compatible graphical user interface (GUI) (e.g. XBoard with PolyGlot, Scid,
Cute Chess, eboard, Arena, Sigma Chess, Shredder, Chess Partner or Fritz) in order
to be used comfortably. Read the documentation for your GUI of choice for information
about how to use Stockfish with it.The Stockfish engine features two evaluation functions for chess, the classical
evaluation based on handcrafted terms, and the NNUE evaluation based on efficiently
updatable neural networks. The classical evaluation runs efficiently on almost all
CPU architectures, while the NNUE evaluation benefits from the vector
intrinsics available on most CPUs (sse2, avx2, neon, or similar).FilesThis distribution of Stockfish consists of the following files:Readme.md, the file you are currently reading.Copying.txt, a text file containing the GNU General Public License version 3.AUTHORS, a text file with the list of authors for the projectsrc, a subdirectory containing the full source code, including a Makefile
that can be used to compile Stockfish on Unix-like systems.a file with the .nnue extension, storing the neural network for the NNUE
evaluation. Binary distributions will have this file embedded.The UCI protocol and available optionsThe Universal Chess Interface (UCI) is a standard protocol used to communicate with
a chess engine, and is the recommended way to do so for typical graphical user interfaces
(GUI) or chess tools. Stockfish implements the majority of it options as described
inthe UCI protocol.Developers can see the default values for UCI options available in Stockfish by typing./stockfish uciin a terminal, but the majority of users will typically see them and
change them via a chess GUI. This is a list of available UCI options in Stockfish:ThreadsThe number of CPU threads used for searching a position. For best performance, set
this equal to the number of CPU cores available.HashThe size of the hash table in MB. It is recommended to set Hash after setting Threads.Clear HashClear the hash table.PonderLet Stockfish ponder its next move while the opponent is thinking.MultiPVOutput the N best lines (principal variations, PVs) when searching.
Leave at 1 for best performance.Use NNUEToggle between the NNUE and classical evaluation functions. If set to "true",
the network parameters must be available to load from file (see also EvalFile),
if they are not embedded in the binary.EvalFileThe name of the file of the NNUE evaluation parameters. Depending on the GUI the
filename might have to include the full path to the folder/directory that contains the file.
Other locations, such as the directory that contains the binary and the working directory,
are also searched.UCI_AnalyseModeAn option handled by your GUI.UCI_Chess960An option handled by your GUI. If true, Stockfish will play Chess960.UCI_ShowWDLIf enabled, show approximate WDL statistics as part of the engine output.
These WDL numbers model expected game outcomes for a given evaluation and
game ply for engine self-play at fishtest LTC conditions (60+0.6s per game).UCI_LimitStrengthEnable weaker play aiming for an Elo rating as set by UCI_Elo. This option overrides Skill Level.UCI_EloIf enabled by UCI_LimitStrength, aim for an engine strength of the given Elo.
This Elo rating has been calibrated at a time control of 60s+0.6s and anchored to CCRL 40/4.Skill LevelLower the Skill Level in order to make Stockfish play weaker (see also UCI_LimitStrength).
Internally, MultiPV is enabled, and with a certain probability depending on the Skill Level a
weaker move will be played.SyzygyPathPath to the folders/directories storing the Syzygy tablebase files. Multiple
directories are to be separated by ";" on Windows and by ":" on Unix-based
operating systems. Do not use spaces around the ";" or ":".Example:C:\tablebases\wdl345;C:\tablebases\wdl6;D:\tablebases\dtz345;D:\tablebases\dtz6It is recommended to store .rtbw files on an SSD. There is no loss in storing
the .rtbz files on a regular HD. It is recommended to verify all md5 checksums
of the downloaded tablebase files (md5sum -c checksum.md5) as corruption will
lead to engine crashes.SyzygyProbeDepthMinimum remaining search depth for which a position is probed. Set this option
to a higher value to probe less aggressively if you experience too much slowdown
(in terms of nps) due to tablebase probing.Syzygy50MoveRuleDisable to let fifty-move rule draws detected by Syzygy tablebase probes count
as wins or losses. This is useful for ICCF correspondence games.SyzygyProbeLimitLimit Syzygy tablebase probing to positions with at most this many pieces left
(including kings and pawns).Move OverheadAssume a time delay of x ms due to network and GUI overheads. This is useful to
avoid losses on time in those cases.Slow MoverLower values will make Stockfish take less time in games, higher values will
make it think longer.nodestimeTells the engine to use nodes searched instead of wall time to account for
elapsed time. Useful for engine testing.Debug Log FileWrite all communication to and from the engine into a text file.For developers the following non-standard commands might be of interest, mainly useful for debugging:benchttSize threads limit fenFile limitType evalTypePerforms a standard benchmark using various options. The signature of a version (standard node
count) is obtained using all defaults.benchis currentlybench 16 1 13 default depth mixed.compilerGive information about the compiler and environment used for building a binary.dDisplay the current position, with ascii art and fen.evalReturn the evaluation of the current position.export_net [filename]Exports the currently loaded network to a file.
If the currently loaded network is the embedded network and the filename
is not specified then the network is saved to the file matching the name
of the embedded network, as defined in evaluate.h.
If the currently loaded network is not the embedded network (some net set
through the UCI setoption) then the filename parameter is required and the
network is saved into that file.flipFlips the side to move.A note on classical evaluation versus NNUE evaluationBoth approaches assign a value to a position that is used in alpha-beta (PVS) search
to find the best move. The classical evaluation computes this value as a function
of various chess concepts, handcrafted by experts, tested and tuned using fishtest.
The NNUE evaluation computes this value with a neural network based on basic
inputs (e.g. piece positions only). The network is optimized and trained
on the evaluations of millions of positions at moderate search depth.The NNUE evaluation was first introduced in shogi, and ported to Stockfish afterward.
It can be evaluated efficiently on CPUs, and exploits the fact that only parts
of the neural network need to be updated after a typical chess move.The nodchip repositoryprovides additional
tools to train and develop the NNUE networks. On CPUs supporting modern vector instructions
(avx2 and similar), the NNUE evaluation results in much stronger playing strength, even
if the nodes per second computed by the engine is somewhat lower (roughly 80% of nps
is typical).Notes:the NNUE evaluation depends on the Stockfish binary and the network parameter
file (see the EvalFile UCI option). Not every parameter file is compatible with a given
Stockfish binary, but the default value of the EvalFile UCI option is the name of a network
that is guaranteed to be compatible with that binary.to use the NNUE evaluation, the additional data file with neural network parameters
needs to be available. Normally, this file is already embedded in the binary or it
can be downloaded. The filename for the default (recommended) net can be found as the default
value of theEvalFileUCI option, with the formatnn-[SHA256 first 12 digits].nnue(for instance,nn-c157e0a5755b.nnue). This file can be downloaded fromhttps://tests.stockfishchess.org/api/nn/[filename]replacing[filename]as needed.What to expect from the Syzygy tablebases?If the engine is searching a position that is not in the tablebases (e.g.
a position with 8 pieces), it will access the tablebases during the search.
If the engine reports a very large score (typically 153.xx), this means
it has found a winning line into a tablebase position.If the engine is given a position to search that is in the tablebases, it
will use the tablebases at the beginning of the search to preselect all
good moves, i.e. all moves that preserve the win or preserve the draw while
taking into account the 50-move rule.
It will then perform a search only on those moves.The engine will not move
immediately, unless there is only a single good move.The engine likely
will not report a mate score, even if the position is known to be won.It is therefore clear that this behaviour is not identical to what one might
be used to with Nalimov tablebases. There are technical reasons for this
difference, the main technical reason being that Nalimov tablebases use the
DTM metric (distance-to-mate), while the Syzygy tablebases use a variation of the
DTZ metric (distance-to-zero, zero meaning any move that resets the 50-move
counter). This special metric is one of the reasons that the Syzygy tablebases are
more compact than Nalimov tablebases, while still storing all information
needed for optimal play and in addition being able to take into account
the 50-move rule.Large PagesStockfish supports large pages on Linux and Windows. Large pages make
the hash access more efficient, improving the engine speed, especially
on large hash sizes. Typical increases are 5..10% in terms of nodes per
second, but speed increases up to 30% have been measured. The support is
automatic. Stockfish attempts to use large pages when available and
will fall back to regular memory allocation when this is not the case.Support on LinuxLarge page support on Linux is obtained by the Linux kernel
transparent huge pages functionality. Typically, transparent huge pages
are already enabled, and no configuration is needed.Support on WindowsThe use of large pages requires "Lock Pages in Memory" privilege. SeeEnable the Lock Pages in Memory Option (Windows)on how to enable this privilege, then runRAMMapto double-check that large pages are used. We suggest that you reboot
your computer after you have enabled large pages, because long Windows
sessions suffer from memory fragmentation, which may prevent Stockfish
from getting large pages: a fresh session is better in this regard.Compiling Stockfish yourself from the sourcesStockfish has support for 32 or 64-bit CPUs, certain hardware
instructions, big-endian machines such as Power PC, and other platforms.On Unix-like systems, it should be easy to compile Stockfish
directly from the source code with the included Makefile in the foldersrc. In general it is recommended to runmake helpto see a list of make
targets with corresponding descriptions.cd src
    make help
    make net
    make build ARCH=x86-64-modernWhen not using the Makefile to compile (for instance, with Microsoft MSVC) you
need to manually set/unset some switches in the compiler command line; see
filetypes.hfor a quick reference.When reporting an issue or a bug, please tell us which Stockfish version
and which compiler you used to create your executable. This information
can be found by typing the following command in a console:./stockfish compilerUnderstanding the code base and participating in the projectStockfish's improvement over the last decade has been a great community
effort. There are a few ways to help contribute to its growth.Donating hardwareImproving Stockfish requires a massive amount of testing. You can donate
your hardware resources by installing theFishtest Workerand view the current tests onFishtest.Improving the codeIf you want to help improve the code, there are several valuable resources:In this wiki,many techniques used in
Stockfish are explained with a lot of background information.The section on Stockfishdescribes many features and techniques used by Stockfish. However, it is
generic rather than being focused on Stockfish's precise implementation.
Nevertheless, a helpful resource.The latest source can always be found onGitHub.
Discussions about Stockfish take place these days mainly in theFishCookinggroup and on theStockfish Discord channel.
The engine testing is done onFishtest.
If you want to help improve Stockfish, please read thisguidelinefirst, where the basics of Stockfish development are explained.Terms of useStockfish is free, and distributed under theGNU General Public License version 3(GPL v3). Essentially, this means you are free to do almost exactly
what you want with the program, including distributing it among your
friends, making it available for download from your website, selling
it (either by itself or as part of some bigger software package), or
using it as the starting point for a software project of your own.The only real limitation is that whenever you distribute Stockfish in
some way, you MUST always include the full source code, or a pointer
to where the source code can be found, to generate the exact binary
you are distributing. If you make any changes to the source code,
these changes must also be made available under the GPL.For full details, read the copy of the GPL v3 found in the file namedCopying.txt.