Universal Chess Interface

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The Universal Chess Interface (UCI) is an open communication protocol that enables chess engines to communicate with user interfaces. [1] [2]

Contents

History

In November 2000, the UCI protocol was released. Designed by Rudolf Huber and Stefan Meyer-Kahlen, the author of Shredder, UCI rivals the older "Chess Engine Communication Protocol" introduced with XBoard/WinBoard.

In 2002, Chessbase, the chess software company which markets Fritz, began to support UCI, which had previously been supported by only a few interfaces and engines.

As of 2021, well over 300 engines are known to directly support UCI.

Design

By design, UCI assigns some tasks to the user interface (i.e., presentation layer) which have traditionally been handled by the engine (at the business layer) itself.[ citation needed ]

Most notably, the opening book is usually expected to be handled by the UI, by simply selecting moves to play until it is out of book, and only then starting up the engine for calculation in the resulting position. UCI does not specify any on-disk format for the opening book. Different UIs usually have their own proprietary formats.[ citation needed ]

While the UI can also take responsibility for handling endgame tablebases, this is arguably better handled in the engine itself, as having tablebase information can be useful for considering possible future positions. [3]

Stefan-Meyer Kahlen's UCI protocol in Shredder uses a variation of long algebraic notation for moves. A "nullmove" from an engine to a GUI should be sent as 0000. [4]

Examples

Commands

There are many commands used to communicate with an engine. [5]

UCI Commands List [5]
CommandUsageDescriptionResponse
quit quit Closes the chess engineN/a
uci uci Tells the engine to switch to UCI modeuciok
ucinewgame ucinewgame Used to let the engine know that the next position it receives will be from a different game.N/a
isready isready Used to synchronize the engine. Use after sending a command that might take some time.readyok
setoption setoption name <id> [value <x>] Used to change the internal parameters of a chess engine.N/a
position position [fen <fenstring> | startpos ] moves <move1> .... <movei>Used to tell the engine to setup the provided position.N/a
go go [infinite | depth <depth> | nodes | mate] searchmoves <move1> .... <movei> ponder wtime <x> btime <x> winc <x> binc <x> movestogo <x> nodes <x> movetime <x> perft <x>Tells the engine to start calculation. bestmove <move> ponder <expected>
stop stop Tells the engine to halt calculation as soon as possible.N/a
ponderhit ponderhit Tells the engine that the player has played the expected move.N/a

There are also some optional commands implemented in engines like Stockfish. [5]

Optional UCI Commands [5]
CommandUsageDescriptionResponse
bench bench [ttSize] [threads] [limit] [fenFile] [limitType] Runs a benchmark test on the engine.Test data
speedtest speedtest [threads] [hash (MiB)] [runtime (s)] Measures the speed of the computer running the engine.Test data
d d Prints an ASCII representation of the board in the current state.ASCII Board
eval eval Displays the static evaluation of the board.Scaled Evaluation
compiler compiler Prints information about the engine's compiler.Compiler info
export_net export_net [filenameBigNet] [filenameSmallNet] Exports the currently loaded network into a file.N/a
flip flip Flips the side to move.N/a
help help In Stockfish, this command prints information about the chess engine and links to the Github.Help text.
license license Same as help command.Help text.

Features

The uci_limitstrength parameter tells engines with this feature to play at a lower level. The uci_elo parameter specifies the Elo rating at which the engine will aim to play. Engines that have implemented uci_elo include Delfi, Fritz, Hiarcs, Houdini, Junior, Rybka, Shredder, Sjeng and Stockfish.

Variants

The UCI has been modified to play some other games, and chess variants. Some of these are: [6]

Each of these protocols may also define variants of Portable Game Notation (PGN) and Forsyth–Edwards Notation (FEN). The XBoard CECP is said to require far fewer changes to support variants. [6]

See also

References

  1. ↑ "Chess engines". Business World Online. 2017-04-06. Archived from the original on 2021-01-28. Retrieved 2018-06-14.
  2. ↑ Torres, JC (2014-06-23). "Lichess embraces blind players with new chess site features". SlashGear. Retrieved 2018-06-14.
  3. ↑ Chess Life. United States Chess Federation. 2003.
  4. ↑ "UCI protocol". www.wbec-ridderkerk.nl. Retrieved 2018-06-14.
  5. 1 2 3 4 "UCI & Commands | Stockfish Docs". Stockfish Documentation. 2025-11-23. Retrieved 2026-02-02.
  6. 1 2 Evert. "UCI protocol for chess variants". TalkChess.com.
  7. ↑ "The Universal Shogi Interface (USI)". hgm.nubati.net.
  8. ↑ "中国象棋电脑应用规范(五)：中国象棋通用引擎协议". www.xqbase.com.
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