setoption

Setoption is a command used within the Universal Chess Interface (UCI) protocol to configure engine options at runtime. It allows a graphical user interface or controller to modify engine parameters such as hash size, the number of threads, or other search-related settings without restarting the engine. The command is part of the standard UCI workflow, which also includes an initial handshaking and option listing from the engine.

Syntax and behavior: the command follows the form setoption name <option name> value <value>. The option name must match a label defined by the engine, and the value’s type depends on that option (for example, integer, boolean, string, or an enumeration). Some engines expose multiple options that can be adjusted during a session, while others may restrict changes to startup time only. If an option is not recognized or the value is invalid, the engine may ignore the request or reply with an error message.

Examples:

- setoption name Hash value 256

- setoption name Threads value 4

- setoption name Ponder value true

Engine behavior and compatibility: not all engines support every option, and some options may require a particular state (such as being idle or not pondering) to take effect. Engines typically respond to setoption with no explicit confirmation, or they may reflect the new setting in subsequent option listings. Clients using setoption should handle potential errors or no-ops gracefully.

Relation to broader protocols: setoption is one of several mechanisms in UCI for configuring engines, complementing the initial option discovery and subsequent runtime queries. It helps tailor engine behavior for different hardware, time controls, or user preferences.

See also: UCI protocol, chess engine options.