Fairy-Stockfish is a chess variant engine derived from [Stockfish](https://github.com/official-stockfish/Stockfish/) designed 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 as [games with user-defined rules](https://github.com/ianfab/Fairy-Stockfish/wiki/Variant-configuration). For [compatibility with graphical user interfaces](https://github.com/ianfab/Fairy-Stockfish/wiki/Usage) it supports the UCI, UCCI, USI, 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 the [playing strength](https://github.com/ianfab/Fairy-Stockfish/wiki/Playing-strength) is 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.
You can download the [Windows executable](https://github.com/ianfab/Fairy-Stockfish/releases/latest/download/fairy-stockfish-largeboard_x86-64.exe) or [Linux binary](https://github.com/ianfab/Fairy-Stockfish/releases/latest/download/fairy-stockfish-largeboard_x86-64) from the [latest release](https://github.com/ianfab/Fairy-Stockfish/releases/latest) or [compile the program from source](https://github.com/ianfab/Fairy-Stockfish#compiling-stockfish-yourself-from-the-sources). The program comes without a graphical user interface, so you perhaps want to use it together with a [compatible GUI](https://github.com/ianfab/Fairy-Stockfish/wiki/Usage#guis), or play against it right away online at [pychess](https://www.pychess.org/). Read more about [how to use](https://github.com/ianfab/Fairy-Stockfish/wiki/Usage) Fairy-Stockfish in the wiki.
If you appreciate this project, please consider to support it by [donating via paypal](https://paypal.me/FairyStockfish), by [contributing CPU time](https://github.com/ianfab/fishtest/wiki) to the framework for testing of code improvements, or by [contributing to the code](https://github.com/ianfab/Fairy-Stockfish/wiki/Contributing) or documentation.
## Supported games
The games currently supported besides chess are listed below. Fairy-Stockfish can also play user-defined variants loaded via a variant configuration file, see the file [`src/variants.ini`](https://github.com/ianfab/Fairy-Stockfish/blob/master/src/variants.ini) and the [wiki](https://github.com/ianfab/Fairy-Stockfish/wiki/Variant-configuration).
### Regional and historical games
- [Xiangqi](https://en.wikipedia.org/wiki/Xiangqi), [Manchu](https://en.wikipedia.org/wiki/Manchu_chess), [Minixiangqi](http://mlwi.magix.net/bg/minixiangqi.htm), [Supply chess](https://en.wikipedia.org/wiki/Xiangqi#Variations)
- [Shogi](https://en.wikipedia.org/wiki/Shogi), [Shogi variants](https://github.com/ianfab/Fairy-Stockfish#shogi-variants)
- [Makruk](https://en.wikipedia.org/wiki/Makruk), [ASEAN](http://hgm.nubati.net/rules/ASEAN.html), Makpong, Ai-Wok
- [Ouk Chatrang](https://en.wikipedia.org/wiki/Makruk#Cambodian_chess), [Kar Ouk](https://en.wikipedia.org/wiki/Makruk#Cambodian_chess)
- [Shatar](https://en.wikipedia.org/wiki/Shatar), [Jeson Mor](https://en.wikipedia.org/wiki/Jeson_Mor)
- [Shatranj](https://en.wikipedia.org/wiki/Shatranj), [Courier](https://en.wikipedia.org/wiki/Courier_chess)
### Chess variants
- [Capablanca](https://en.wikipedia.org/wiki/Capablanca_Chess), [Janus](https://en.wikipedia.org/wiki/Janus_Chess), [Modern](https://en.wikipedia.org/wiki/Modern_Chess_(chess_variant)), [Chancellor](https://en.wikipedia.org/wiki/Chancellor_Chess), [Embassy](https://en.wikipedia.org/wiki/Embassy_Chess), [Gothic](https://www.chessvariants.com/large.dir/gothicchess.html), [Capablanca random chess](https://en.wikipedia.org/wiki/Capablanca_Random_Chess)
- [Grand](https://en.wikipedia.org/wiki/Grand_Chess), [Shako](https://www.chessvariants.com/large.dir/shako.html), [Centaur](https://www.chessvariants.com/large.dir/contest/royalcourt.html)
- [Chess960](https://en.wikipedia.org/wiki/Chess960), [Placement/Pre-Chess](https://www.chessvariants.com/link/placement-chess)
- [Crazyhouse](https://en.wikipedia.org/wiki/Crazyhouse), [Loop](https://en.wikipedia.org/wiki/Crazyhouse#Variations), [Chessgi](https://en.wikipedia.org/wiki/Crazyhouse#Variations), [Pocket Knight](http://www.chessvariants.com/other.dir/pocket.html), Capablanca-Crazyhouse
- [Bughouse](https://en.wikipedia.org/wiki/Bughouse_chess), [Koedem](http://schachclub-oetigheim.de/wp-content/uploads/2016/04/Koedem-rules.pdf)
- [Seirawan](https://en.wikipedia.org/wiki/Seirawan_chess), Seirawan-Crazyhouse
- [Amazon](https://en.wikipedia.org/wiki/Amazon_(chess)), [Chigorin](https://en.wikipedia.org/wiki/Chigorin_Chess), [Almost chess](https://en.wikipedia.org/wiki/Almost_Chess)
- [Hoppel-Poppel](http://www.chessvariants.com/diffmove.dir/hoppel-poppel.html), New Zealand
- [Antichess](https://lichess.org/variant/antichess), [Giveaway](http://www.chessvariants.com/diffobjective.dir/giveaway.old.html), [Suicide](https://www.freechess.org/Help/HelpFiles/suicide_chess.html), [Losers](https://www.chessclub.com/help/Wild17), [Codrus](http://www.binnewirtz.com/Schlagschach1.htm)
- [Extinction](https://en.wikipedia.org/wiki/Extinction_chess), [Kinglet](https://en.wikipedia.org/wiki/V._R._Parton#Kinglet_Chess), Three Kings Chess
- [King of the Hill](https://en.wikipedia.org/wiki/King_of_the_Hill_(chess)), [Racing Kings](https://en.wikipedia.org/wiki/V._R._Parton#Racing_Kings)
- [Three-check](https://en.wikipedia.org/wiki/Three-check_chess), Five-check
- [Los Alamos](https://en.wikipedia.org/wiki/Los_Alamos_chess)
### Shogi variants
- [Minishogi](https://en.wikipedia.org/wiki/Minishogi), [EuroShogi](https://en.wikipedia.org/wiki/EuroShogi), [Judkins shogi](https://en.wikipedia.org/wiki/Judkins_shogi)
- [Kyoto shogi](https://en.wikipedia.org/wiki/Kyoto_shogi), [Microshogi](https://en.wikipedia.org/wiki/Micro_shogi)
- [Dobutsu shogi](https://en.wikipedia.org/wiki/Dōbutsu_shōgi), [Goro goro shogi](https://en.wikipedia.org/wiki/D%C5%8Dbutsu_sh%C5%8Dgi#Variation)
### Related games
See the [Fairy-Stockfish Wiki](https://github.com/ianfab/Fairy-Stockfish/wiki) for more info, or if the required information is not available, open an [issue](https://github.com/ianfab/Fairy-Stockfish/issues).
[Stockfish](https://stockfishchess.org) is a free, powerful UCI chess engine
derived from Glaurung 2.1. It is not a complete chess program and requires a
UCI-compatible 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.
This 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.
* src, a subdirectory containing the full source code, including a Makefile
that can be used to compile Stockfish on Unix-like systems.
## UCI parameters
Currently, Stockfish has the following UCI options:
* #### Debug Log File
Write all communication to and from the engine into a text file.
* #### Contempt
A positive value for contempt favors middle game positions and avoids draws.
* #### Analysis Contempt
By default, contempt is set to prefer the side to move. Set this option to "White"
or "Black" to analyse with contempt for that side, or "Off" to disable contempt.
* #### Threads
The number of CPU threads used for searching a position. For best performance, set
this equal to the number of CPU cores available.
* #### Hash
The size of the hash table in MB.
* #### Clear Hash
Clear the hash table.
* #### Ponder
Let Stockfish ponder its next move while the opponent is thinking.
* #### MultiPV
Output the N best lines (principal variations, PVs) when searching.
Leave at 1 for best performance.
* #### Skill Level
Lower 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.
* #### UCI_LimitStrength
Enable weaker play aiming for an Elo rating as set by UCI_Elo. This option overrides Skill Level.
* #### UCI_Elo
If 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.
* #### Move Overhead
Assume a time delay of x ms due to network and GUI overheads. This is useful to
avoid losses on time in those cases.
* #### Minimum Thinking Time
Search for at least x ms per move.
* #### Slow Mover
Lower values will make Stockfish take less time in games, higher values will
make it think longer.
* #### nodestime
Tells the engine to use nodes searched instead of wall time to account for
elapsed time. Useful for engine testing.
* #### UCI_Chess960
An option handled by your GUI. If true, Stockfish will play Chess960.
* #### UCI_AnalyseMode
An option handled by your GUI.
* #### SyzygyPath
Path 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 ":".
It 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.
* #### SyzygyProbeDepth
Minimum remaining search depth for which a position is probed. Set this option
to a higher value to probe less agressively if you experience too much slowdown
(in terms of nps) due to TB probing.
* #### Syzygy50MoveRule
Disable to let fifty-move rule draws detected by Syzygy tablebase probes count
as wins or losses. This is useful for ICCF correspondence games.
* #### SyzygyProbeLimit
Limit Syzygy tablebase probing to positions with at most this many pieces left
(including kings and pawns).
## What to expect from Syzygybases?
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
that 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 Syzygybases 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 Syzygybases 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.
## Compiling Stockfish yourself from the sources
On Unix-like systems, it should be possible to compile Stockfish
directly from the source code with the included Makefile.
Stockfish has support for 32 or 64-bit CPUs, the hardware POPCNT
instruction, big-endian machines such as Power PC, and other platforms.
In general it is recommended to run `make help` to see a list of make
targets with corresponding descriptions. When 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 file *types.h*
for a quick reference.
When reporting an issue or a bug, please tell us which version and
compiler you used to create your executable. These informations can
be found by typing the following commands in a console:
## Understanding the code base and participating in the project
Stockfish's improvement over the last couple of years has been a great
community effort. There are a few ways to help contribute to its growth.
### Donating hardware
Improving Stockfish requires a massive amount of testing. You can donate
your hardware resources by installing the [Fishtest Worker](https://github.com/glinscott/fishtest/wiki/Running-the-worker:-overview)
and view the current tests on [Fishtest](https://tests.stockfishchess.org/tests).
### Improving the code
If you want to help improve the code, there are several valuable resources:
* [In this wiki,](https://www.chessprogramming.org) many techniques used in
Stockfish are explained with a lot of background information.
* [The section on Stockfish](https://www.chessprogramming.org/Stockfish)
describes 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 on [GitHub](https://github.com/official-stockfish/Stockfish).
Discussions about Stockfish take place in the [FishCooking](https://groups.google.com/forum/#!forum/fishcooking)
group and engine testing is done on [Fishtest](https://tests.stockfishchess.org/tests).
If you want to help improve Stockfish, please read this [guideline](https://github.com/glinscott/fishtest/wiki/Creating-my-first-test)
first, where the basics of Stockfish development are explained.
Stockfish is free, and distributed under the **GNU General Public License version 3**
(GPL v3). Essentially, this means that 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 web site, 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. 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 named