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 from the list in EvalFile based on comparison of the variant name with the prefix of the file name, therefore you do not need to reset this option when switching variants. For all variants except chess the file name has to start with the variant name. For standard chess, nn- is 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.