Settings

UCI options

The following UCI options are added or changed compared to official Stockfish. See the list of UCI options of official Stockfish for details on other options.

• UCI_Variant

  The most important option, since it allows to set the variant that is going to be played. Most GUIs for chess variants set this option automatically if you select a variant in the GUI, but in case of usage via the CLI the option needs to be set manually.

• UCI_Chess960

  Used as a universal flag to switch between Chess960-style shuffling variants (such as Crazyhouse960, S-Chess960/2880, Capablanca Random Chess, etc.) and the respective normal variant. For variants without castling, this option does not have any effect.

• Protocol

  Can be used to switch between the supported protocols, namely UCI, UCCI (Xiangqi), USI (Shogi) and XBoard/CECP. This option is automatically set to the respective protocol if communication is started with one of the uci/ucci/usi/xboard commands (as required by the protocols).

• VariantPath

  The path to the configuration file for user-defined variants. This parameter internally is also set by the load command, which is the preferred way of loading variants, since it helps the GUI to update its UCI_Variant selection list.

• TsumeMode

  When enabled assumes that the side without a king has to strive for a forced mate, and otherwise loses. This option should be enabled when solving Tsume puzzles, otherwise it might wrongly go for a brinkmate. Although it mainly targets Shogi, the option can be used for any variant where checkmate is the goal.

• EvalFile

  The name of the NNUE evaluation parameter file. Since an NNUE file is only valid for a specific variant, in Fairy-Stockfish the EvalFile option can be a list of NNUE files. Multiple files are to be separated by ; on Windows and by : on Unix-based operating systems. Do not use spaces around the ; or :.

  Example: nn-2eb2e0707c2b.nnue;kingofthehill-86a538a53974.nnue

  Fairy-Stockfish automatically selects the matching NNUE file when loading a variant based on the prefix of the file name. For all variants except chess the file name has to start with the variant name. For standard chess, nn- is also accepted as prefix.

  Depending on the location on the file system, 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.