-### Overview
+## Overview
-Stockfish is a free UCI chess engine derived from Glaurung 2.1. It is
-not a complete chess program and requires some UCI-compatible GUI
-(e.g. XBoard with PolyGlot, 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.
+[](https://travis-ci.org/official-stockfish/Stockfish)
+[](https://ci.appveyor.com/project/mcostalba/stockfish)
-This version of Stockfish supports up to 64 CPUs, but has not been
-tested thoroughly with more than 4. The program tries to detect the
-number of CPUs on your computer and sets the number of search threads
-accordingly, but please be aware that the detection is not always
-correct. It is therefore recommended to inspect the value of the
-*Threads* UCI parameter, and to make sure it equals the number of CPU
-cores on your computer. If you are using more than eight threads, it is
-recommended to raise the value of the *Min Split Depth* UCI parameter to 7.
+[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.
-### Files
+## Files
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.
+ * 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.
+
+ * #### 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.
- * src/, a subdirectory containing the full source code, including a Makefile
- that can be used to compile Stockfish on Unix-like systems. For further
- information about how to compile Stockfish yourself read section below.
+ * #### nodestime
+ Tells the engine to use nodes searched instead of wall time to account for
+ elapsed time. Useful for engine testing.
- * polyglot.ini, for using Stockfish with Fabien Letouzey's PolyGlot
- adapter.
+ * #### UCI_Chess960
+ An option handled by your GUI. If true, Stockfish will play Chess960.
+ * #### UCI_AnalyseMode
+ An option handled by your GUI.
-### Opening books
+ * #### 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 ":".
+
+ Example: `C:\tablebases\wdl345;C:\tablebases\wdl6;D:\tablebases\dtz345;D:\tablebases\dtz6`
+
+ 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.
-This version of Stockfish has support for PolyGlot opening books. For
-information about how to create such books, consult the PolyGlot
-documentation. The book file can be selected by setting the *Book File*
-UCI parameter.
+ * #### 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.
-### Compiling it yourself
+ * #### 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.
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 Makefile to
+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.
-### Terms of use
+## 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)
+and view the current tests on [Fishtest](http://tests.stockfishchess.org/tests).
+
+### Improving the code
+
+If you want to help improve the code, there are several valuable ressources:
+
+* [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](http://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.
+
+
+## Terms of use
-Stockfish is free, and distributed under the **GNU General Public License**
-(GPL). Essentially, this means that you are free to do almost exactly
+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
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 found in the file named
-*Copying.txt*
+For full details, read the copy of the GPL v3 found in the file named
+*Copying.txt*.
projects / stockfish / blobdiff