There exist at least two variations of UCI, one for Shogi (USI, originally by Tord Romstad) and one for Xiangqi (UCCI, originally by Huang Chen, I think) although apparently both can be played through variations of normal UCI as well.
There is also at least some interest in UCI engines that play (slightly modified) versions of regular chess (for instance the special Stockfish version discussed in http://www.talkchess.com/forum/viewtopic.php?t=53885).
My goal for this thread is two-fold:
- To collect in one place, for easy reference, a description of the different UCI dialects, how they differ and how they are similar.
- To propose, further down, a mechanism by which UCI could be used to play chess variants
Ultimately, I hope that this will encourage more people to develop chess variant engines.
To play a chess variant, two things are needed: an engine that plays it, and a GUI that can communicate with it. Clearly, there are currently no UCI GUIs that really support chess variants, but I hope that defining a way for UCI engines to use variants can be a first step to changing that.
Probably the first GUI that would support UCI chess variant engines would actually be XBoard.
So, to kick off, here is my unified description of UCI/USI/UCCI (which is basically an edit of the original UCI spec with the differences spliced in). The most current version can be found at http://www.eglebbk.dds.nl/ustari_protocol.txt
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Nomenclature ------------ UCI: players are called "white" and "black". White begins. squares are labelled a1,b1,...g8,h8, from lower left to upper right. Pieces are "PNBRQK", upper case for white and lower case for black. USI: players are called "white" and "black". Black begins. squares are labelled 9i,8i...2a,1a, from lower left to upper right. Pieces are "PLNSGBRK", upper case for black and lower case for white. (This actually matches UCI in that upper case is for the side that moves first). Promoted pieces are preceded by a "+" (so +P, +R). UCCI: players are called "white" and "black". White begins. squares are labelled a0,b0,...h9,i9, from lower left to upper right. Pieces are "PABNCRK", upper case for white and lower case for black. Move format ----------- In all cases, moves are encoded as <from square><to square>[<suffix>]. The squares are encoded as mentioned above. The suffix is optional and used to indicate promotions: it is the (lower case) letter of the promotion choice in chess and a + in Shogi (where there is only one choice). Xiangqi doesn't have promotions as such. Castling is encoded as a two-step king move, or as "KxR" for Fischer chess. Piece drops are encoded as <token>*<square>, where <token> is the upper case piece letter and <square> is the drop square. From GUI to engine ------------------ * uci, usi, ucci tell engine to use the uci (universal chess interface) or one of its dialects, this will be sent once as a first command after program boot to tell the engine to switch to uci mode. After receiving the uci command the engine must identify itself with the "id" command and send the "option" commands to tell the GUI which engine settings the engine supports if any. After that the engine should send "uciok" ("usiok", "ucciok") to acknowledge the uci mode. If no uciok is sent within a certain time period, the engine task will be killed by the GUI. In ucci mode, the list of options should at least include "option usemillisec type check default false" "option newgame type button" * debug [ on | off ] switch the debug mode of the engine on and off. In debug mode the engine should send additional infos to the GUI, e.g. with the "info string" command, to help debugging, e.g. the commands that the engine has received etc. This mode should be switched off by default and this command can be sent any time, also when the engine is thinking. * isready this is used to synchronize the engine with the GUI. When the GUI has sent a command or multiple commands that can take some time to complete, this command can be used to wait for the engine to be ready again or to ping the engine to find out if it is still alive. E.g. this should be sent after setting the path to the tablebases as this can take some time. This command is also required once before the engine is asked to do any search to wait for the engine to finish initializing. This command must always be answered with "readyok" and can be sent also when the engine is calculating in which case the engine should also immediately answer with "readyok" without stopping the search. * setoption name <id> [value <x>] (UCI, USI) this is sent to the engine when the user wants to change the internal parameters of the engine. For the "button" type no value is needed. One string will be sent for each parameter and this will only be sent when the engine is waiting. The name and value of the option in <id> should not be case sensitive and can inlude spaces in UCI (but not in USI). The substrings "value" and "name" should be avoided in <id> and <x> to allow unambiguous parsing, for example do not use <name> = "draw value". Here are some strings for the example below: "setoption name Nullmove value true\n" "setoption name Selectivity value 3\n" "setoption name Style value Risky\n" "setoption name Clear Hash\n" "setoption name NalimovPath value c:\chess\tb\4;c:\chess\tb\5\n" * setoption <id> [<x>] (UCCI) this is sent to the engine when the user wants to change the internal parameters of the engine. For the "button" type no value is needed. One string will be sent for each parameter and this will only be sent when the engine is waiting. The name and value of the option in <id> should not be case sensitive and can NOT inlude spaces. The name should preferentially be all in lower case. Here are some strings for the example below: "setoption nullmove true\n" "setoption selectivity 3\n" "setoption style Risky\n" "setoption clear Hash\n" "setoption nalimovpath c:\chess\tb\4;c:\chess\tb\5\n" * register this is the command to try to register an engine or to tell the engine that registration will be done later. This command should always be sent if the engine has sent "registration error" at program startup. The following tokens are allowed: * later the user doesn't want to register the engine now. * name <x> the engine should be registered with the name <x> * code <y> the engine should be registered with the code <y> Example: "register later" "register name Stefan MK code 4359874324" * ucinewgame, usinewgame (UCI, USI) this is sent to the engine when the next search (started with "position" and "go") will be from a different game. This can be a new game the engine should play or a new game it should analyse but also the next position from a testsuite with positions only. If the GUI hasn't sent a "ucinewgame" before the first "position" command, the engine shouldn't expect any further ucinewgame commands as the GUI is probably not supporting the ucinewgame command. So the engine should not rely on this command even though all new GUIs should support it. As the engine's reaction to "ucinewgame" can take some time the GUI should always send "isready" after "ucinewgame" to wait for the engine to finish its operation. * setoption newgame (UCCI) See usinewgame above. Note that the engine most define this option for it to be sent. * position [fen <fenstring> | startpos ] moves <move1> .... <movei> (UCI) set up the position described in fenstring on the internal board and play the moves on the internal chess board. if the game was played from the start position the string "startpos" will be sent Note: no "new" command is needed. However, if this position is from a different game than the last position sent to the engine, the GUI should have sent a "ucinewgame" inbetween. * fen <fenstring> moves <move1> .... <movei> (UCI-cyclone) As "position fen" above. * position [sfen <fenstring> | startpos ] moves <move1> .... <movei> (USI) as above, but sends sfen rather than FEN. Moves use Shogi-style square names. To be safe, it is better to not use startpos at all (not all engines understand it) and always set the postion using a FEN string. * position fen <fenstring> moves <move1> .... <movei> (UCCI) as above. Uses normal FEN for Xiangqi (with piece names RNBACPK). Moves use Western-style square names. The square on the lower-left hand side of the first player ("white") is "a0", the upper-right is "i9". The FEN string includes fields for en-passant and castling (both -, obviously). Normally, the interface is expected to send the FEN for the position after the last irreversible move, and the move history from that point onward. This to reduce the amount of traffic between engine and GUI. Note there is no "startpos"! * probe [ fen <fenstring> | startpos ] moves <move1> .... <movei> (UCCI) Tell the engine to spit out whatever it found about the current position in its hash table (using the "pophash" response). Apparently for debugging only. For some reason "startpos" is possible here (probably a mistake). * banmoves <move1> .... <movei> (UCCI) exclude the listed moves from consideration in the current position. This is useful for analysis, but the GUI may also use this to send moves that represent illegal chases. This allows engines to not implement the (full) chasing rules, and rely on the GUI instead. * go (UCI, USI, UCCI) start calculating on the current position set up with the "position" command. There are a number of commands that can follow this command, all will be sent in the same string. If one command is not sent its value should be interpreted as it would not influence the search. * searchmoves <move1> .... <movei> restrict search to this moves only Example: After "position startpos" and "go infinite searchmoves e2e4 d2d4" the engine should only search the two moves e2e4 and d2d4 in the initial position. * draw (UCCI) The engine has received a draw offer. * ponder start searching in pondering mode. Do not exit the search in ponder mode, even if it's mate! This means that the last move sent in in the position string is the ponder move. The engine can do what it wants to do, but after a "ponderhit" command it should execute the suggested move to ponder on. This means that the ponder move sent by the GUI can be interpreted as a recommendation about which move to ponder. However, if the engine decides to ponder on a different move, it should not display any mainlines as they are likely to be misinterpreted by the GUI because the GUI expects the engine to ponder on the suggested move. * wtime <x> (UCI, USI) white has x msec left on the clock * btime <x> (UCI, USI) black has x msec left on the clock * winc <x> (UCI, USI) white increment per move in mseconds if x > 0 * binc <x> (UCI, USI) black increment per move in mseconds if x > 0 * movestogo <x> (UCI, USI) there are x moves to the next time control, this will only be sent if x > 0, if you don't get this and get the wtime and btime it's sudden death * movestogo <x> (UCCI) there are x moves to the next time control, if x = 0 it's sudden death * time <x> (UCCI) side to move has x left on the clock x is in s, unless the GUI has sent "option usemillisec true", in which case it is msec * opptime <x> (UCCI) side not on move has x left on the clock x is in s, unless the GUI has sent "option usemillisec true", in which case it is msec * increment <x> (UCCI) side-to-move increment per move in s or msec * oppincrement <x> (UCCI) not side-to-move increment per move in s or msec * oppmovestogo <x> (UCCI) the opponent has x moves to the next time control * depth <x> search x plies only. * nodes <x> search x nodes only, * mate <x> search for a mate in x moves * movetime <x> search exactly x mseconds * byoyomi <x> (USI) search exactly x mseconds if the time (specified by wtime/btime) has been used up * infinite search until the "stop" command. Do not exit the search without being told so in this mode! * stop stop calculating as soon as possible, don't forget the "bestmove" and possibly the "ponder" token when finishing the search * ponderhit the user has played the expected move. This will be sent if the engine was told to ponder on the same move the user has played. The engine should continue searching but switch from pondering to normal search. * ponderhit draw (UCCI) Accept a draw offer while pondering. * quit quit the program as soon as possible * bye (UCCI) finish the calculation, then quit Engine to GUI: -------------- * id * name <x> this must be sent after receiving the "uci" command to identify the engine, e.g. "id name Shredder X.Y\n" * author <x> this must be sent after receiving the "uci" command to identify the engine, e.g. "id author Stefan MK\n" * uciok, usiok, ucciok Must be sent after the id and optional options to tell the GUI that the engine has sent all infos and is ready in uci mode. * readyok This must be sent when the engine has received an "isready" command and has processed all input and is ready to accept new commands now. It is usually sent after a command that can take some time to be able to wait for the engine, but it can be used anytime, even when the engine is searching, and must always be answered with "isready". * bestmove <move1> [ ponder <move2> ] the engine has stopped searching and found the move <move> best in this position. the engine can send the move it likes to ponder on. The engine must not start pondering automatically. this command must always be sent if the engine stops searching, also in pondering mode if there is a "stop" command, so for every "go" command a "bestmove" command is needed! Directly before that the engine should send a final "info" command with the final search information, the the GUI has the complete statistics about the last search. * bestmove <move1> [ ponder <move2> ] [ draw | resign ] (UCCI) as "bestmove" above, but includes a draw offer or resignation by the engine. * bestmove [ draw | resign ] (UCCI) the engine accepts a draw offer, or resigns. * nobestmove (UCCI) The search returned no move. Either there are no legal moves (the game ended), or the engine was interrupted before it could produce a move. Also sent in response to "go depth 0", which prompts the engine to spit out its static evaluation of the current position. * pophash [bestmove <move>] [lowerbound <beta> depth <depth>] [upperbound <alpha> depth <depth>] (UCCI) Response to "probe". Whatever the engine found in its transposition table for the current position. Again apparetly meant as a debugging aid. If the position was not found, leave all fields blank. * copyprotection this is needed for copyprotected engines. After the uciok command the engine can tell the GUI, that it will check the copy protection now. This is done by "copyprotection checking". If the check is ok the engine should send "copyprotection ok", otherwise "copyprotection error". If there is an error the engine should not function properly but should not quit alone. If the engine reports "copyprotection error" the GUI should not use this engine and display an error message instead! The code in the engine can look like this TellGUI("copyprotection checking\n"); // ... check the copy protection here ... if(ok) TellGUI("copyprotection ok\n"); else TellGUI("copyprotection error\n"); * registration this is needed for engines that need a username and/or a code to function with all features. Analog to the "copyprotection" command the engine can send "registration checking" after the uciok command followed by either "registration ok" or "registration error". Also after every attempt to register the engine it should answer with "registration checking" and then either "registration ok" or "registration error". In contrast to the "copyprotection" command, the GUI can use the engine after the engine has reported an error, but should inform the user that the engine is not properly registered and might not use all its features. In addition the GUI should offer to open a dialog to enable registration of the engine. To try to register an engine the GUI can send the "register" command. The GUI has to always answer with the "register" command if the engine sends "registration error" at engine startup (this can also be done with "register later") and tell the user somehow that the engine is not registered. This way the engine knows that the GUI can deal with the registration procedure and the user will be informed that the engine is not properly registered. * info the engine wants to send information to the GUI. This should be done whenever one of the info has changed. The engine can send only selected infos or multiple infos with one info command, e.g. "info currmove e2e4 currmovenumber 1" or "info depth 12 nodes 123456 nps 100000". Also all infos belonging to the pv should be sent together e.g. "info depth 2 score cp 214 time 1242 nodes 2124 nps 34928 pv e2e4 e7e5 g1f3" I suggest to start sending "currmove", "currmovenumber", "currline" and "refutation" only after one second to avoid too much traffic. Additional info: * depth <x> search depth in plies * seldepth <x> selective search depth in plies, if the engine sends seldepth there must also be a "depth" present in the same string. * time <x> the time searched in ms, this should be sent together with the pv. * nodes <x> x nodes searched, the engine should send this info regularly * pv <move1> ... <movei> the best line found * multipv <num> this for the multi pv mode. for the best move/pv add "multipv 1" in the string when you send the pv. in k-best mode always send all k variants in k strings together. * score * cp <x> the score from the engine's point of view in centipawns. * mate <y> mate in y moves (UCI) or plies (USI). If the engine is getting mated use negative values for y. * lowerbound the score is just a lower bound. * upperbound the score is just an upper bound. * currmove <move> currently searching this move * currmovenumber <x> currently searching move number x, for the first move x should be 1 not 0. * hashfull <x> the hash is x permill full, the engine should send this info regularly * nps <x> x nodes per second searched, the engine should send this info regularly * tbhits <x> x positions where found in the endgame table bases * sbhits <x> x positions where found in the shredder endgame databases * cpuload <x> the cpu usage of the engine is x permill. * string <str> any string str which will be displayed be the engine, if there is a string command the rest of the line will be interpreted as <str>. * refutation <move1> <move2> ... <movei> move <move1> is refuted by the line <move2> ... <movei>, i can be any number >= 1. Example: after move d1h5 is searched, the engine can send "info refutation d1h5 g6h5" if g6h5 is the best answer after d1h5 or if g6h5 refutes the move d1h5. if there is no refutation for d1h5 found, the engine should just send "info refutation d1h5" The engine should only send this if the option "UCI_ShowRefutations" is set to true. * currline <cpunr> <move1> ... <movei> this is the current line the engine is calculating. <cpunr> is the number of the cpu if the engine is running on more than one cpu. <cpunr> = 1,2,3.... if the engine is just using one cpu, <cpunr> can be omitted. If <cpunr> is greater than 1, always send all k lines in k strings together. The engine should only send this if the option "UCI_ShowCurrLine" is set to true. * message <message> (UCCI) Whatever other information the engine wants to tell the user. The GUI can display this somewhere. * option This command tells the GUI which parameters can be changed in the engine. This should be sent once at engine startup after the "uci" and the "id" commands if any parameter can be changed in the engine. The GUI should parse this and build a dialog for the user to change the settings. Note that not every option needs to appear in this dialog as some options like "Ponder", "UCI_AnalyseMode", etc. are better handled elsewhere or are set automatically. If the user wants to change some settings, the GUI will send a "setoption" command to the engine. Note that the GUI need not send the setoption command when starting the engine for every option if it doesn't want to change the default value. For all allowed combinations see the examples below, as some combinations of this tokens don't make sense. One string will be sent for each parameter. * name <id> The option has the name id. Certain options have a fixed value for <id>, which means that the semantics of this option is fixed. Usually those options should not be displayed in the normal engine options window of the GUI but get a special treatment. "Pondering" for example should be set automatically when pondering is enabled or disabled in the GUI options. The same for "UCI_AnalyseMode" which should also be set automatically by the GUI. All those certain options have the prefix "UCI_" except for the first 6 options below. If the GUI gets an unknown Option with the prefix "UCI_", it should just ignore it and not display it in the engine's options dialog. * <id> = Hash, type is spin the value in MB for memory for hash tables can be changed, this should be answered with the first "setoptions" command at program boot if the engine has sent the appropriate "option name Hash" command, which should be supported by all engines! So the engine should use a very small hash first as default. * <id> = NalimovPath, type string this is the path on the hard disk to the Nalimov compressed format. Multiple directories can be concatenated with ";" * <id> = NalimovCache, type spin this is the size in MB for the cache for the nalimov table bases These last two options should also be present in the initial options exchange dialog when the engine is booted if the engine supports it * <id> = Ponder, type check this means that the engine is able to ponder. The GUI will send this whenever pondering is possible or not. Note: The engine should not start pondering on its own if this is enabled, this option is only needed because the engine might change its time management algorithm when pondering is allowed. * <id> = OwnBook, type check this means that the engine has its own book which is accessed by the engine itself. if this is set, the engine takes care of the opening book and the GUI will never execute a move out of its book for the engine. If this is set to false by the GUI, the engine should not access its own book. * <id> = MultiPV, type spin the engine supports multi best line or k-best mode. the default value is 1 * <id> = UCI_ShowCurrLine, type check, should be false by default, the engine can show the current line it is calculating. see "info currline" above. * <id> = UCI_ShowRefutations, type check, should be false by default, the engine can show a move and its refutation in a line. see "info refutations" above. * <id> = UCI_LimitStrength, type check, should be false by default, The engine is able to limit its strength to a specific Elo number, This should always be implemented together with "UCI_Elo". * <id> = UCI_Elo, type spin The engine can limit its strength in Elo within this interval. If UCI_LimitStrength is set to false, this value should be ignored. If UCI_LimitStrength is set to true, the engine should play with this specific strength. This should always be implemented together with "UCI_LimitStrength". * <id> = UCI_AnalyseMode, type check The engine wants to behave differently when analysing or playing a game. For example when playing it can use some kind of learning. This is set to false if the engine is playing a game, otherwise it is true. * <id> = UCI_Opponent, type string With this command the GUI can send the name, title, elo and if the engine is playing a human or computer to the engine. The format of the string has to be [GM|IM|FM|WGM|WIM|none] [<elo>|none] [computer|human] <name> Examples: "setoption name UCI_Opponent value GM 2800 human Gary Kasparov" "setoption name UCI_Opponent value none none computer Shredder" * <id> = UCI_EngineAbout, type string With this command, the engine tells the GUI information about itself, for example a license text, usually it doesn't make sense that the GUI changes this text with the setoption command. Example: "option name UCI_EngineAbout type string default Shredder by Stefan Meyer-Kahlen, see www.shredderchess.com" * <id> = UCI_ShredderbasesPath, type string this is either the path to the folder on the hard disk containing the Shredder endgame databases or the path and filename of one Shredder endgame datbase. * <id> = UCI_SetPositionValue, type string the GUI can send this to the engine to tell the engine to use a certain value in centipawns from white's point of view if evaluating this specifix position. The string can have the formats: <value> + <fen> | clear + <fen> | clearall * type <t> The option has type t. There are 5 different types of options the engine can send * check a checkbox that can either be true or false * spin a spin wheel that can be an integer in a certain range * combo a combo box that can have different predefined strings as a value * button a button that can be pressed to send a command to the engine * string a text field that has a string as a value, an empty string has the value "<empty>" * default <x> the default value of this parameter is x * min <x> the minimum value of this parameter is x * max <x> the maximum value of this parameter is x * var <x> a predefined value of this parameter is x Examples: Here are 5 strings for each of the 5 possible types of options "option name Nullmove type check default true\n" "option name Selectivity type spin default 2 min 0 max 4\n" "option name Style type combo default Normal var Solid var Normal var Risky\n" "option name NalimovPath type string default c:\\n" "option name Clear Hash type button\n" Common incompatibilities: ------------------------- UCI: many variant engines (Shogi, Xiangqi) do not understand "startpos". USI: many engines only recognise the following format for the "go" command: "go btime %d wtime %d byoyomi %d" The options winc/binc/movestogo/movetime may cause unpredictabe behaviour, including crashes. many engines only respond to "isready" once, and only allow options to be set before receiving "isready". Standard options (hash, ponder) are not announced, even if they do exist and can be set. UCCI: many engines do not accurately report the options they have. This is particularly problematic for "usemillisec". It is best to always set options explicitly and not trust the defaults. Caveats: -------- * In USI, mate scores are in plies. In UCI and UCCI, mate scores are in moves. * In USI, the first side to move is referred to as "black" (and their clock is referred to by "btime") * In UCCI, the default time unit is in seconds, but there is an option "usemillisec" (which should be supported by all engines, but currently isn't) that can be used to switch it back to one second. * UCI option names can contain spaces and be presented in mixed caps (but should be matched case-insensitive). In USI and UCCI, option names should not contain spaces. In UCCI, they should also all be in lower case. The actual text that is displayed in the engine options is supposed to come from a "translation file". * Make sure to send "movestogo" to UCCI engines: they may assume a default of 1. To set a sudden-death time control in UCCI, send "movestogo 0".
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option name UCI_Variant type combo default Chess var Chess var Fischer Chess var Seirawan Chess var King-of-the-hill var Atomic var Capablanca
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setoption name UCI_Variant value <whatever>
There are a couple of details that would need to be worked out though:
- Simply hard-coding a list of possibly supported variants in the protocol specs seems not very future-proof. XBoard now has "engine defined" variants, but those require some more information to be passed between engine and GUI. How best to handle this?
- Should piece symbols be hard-coded? Globally? Or per variant? To put the problem into perspective: the Archbishop (A) of Capablanca chess is also the Hawk (H) of Seirawan chess. The Ferz of Shatranj is also the Advisor in Xiangqi and the Met of Makruk. Should we define a number of "standard" pieces (moves) and define their names for particular variants (this could be similar to XBoard's pieceToChar)?
So perhaps the best for now is to define the meaning of a set of standard variants, with their pieces and startup FENs?
Thoughts? Ideas? Suggestions?