UCI option

UCI stands for Universal Chess Interface. It is a text protocol that lets a graphical interface, the program showing the board and controls, communicate with a chess engine, the program that calculates moves. A UCI option is a setting the engine exposes to that interface, such as memory size, processing threads, or Chess960 support.

When the interface starts a UCI session, the engine advertises each option with a name, type, and, where relevant, a default value, limits, or allowed choices. The interface can turn that description into a visible control and later send a setoption command to change it. Available options vary by engine and version.

The five UCI option types

• check: a true-or-false value, usually displayed as a checkbox.
• spin: an integer constrained by a minimum and maximum.
• combo: one choice from a predefined set.
• button: a one-time action with no stored value, such as clearing an internal table.
• string: free text, such as a file path.

An option is neither a chess rule nor a promise of universal compatibility. Two engines may use different names, ranges, and values for similar features. Controlling software should read what each engine actually advertises instead of assuming a fixed list.