A toggle is a control used to switch between different states, such as ON and OFF. They are especially useful for changing system settings or preferences (i.e. states of system functionality) and are the preferred control over a radio button or checkbox. A good toggle switch will have a clear label that indicates what the switch will do and what state it is in currently. Toggle switches should be easy to read, utilizing visual cues like movement and color to communicate state. Avoid using colors that rely on low-contrast to convey meaning and consider the societal and cultural implications of the chosen color(s).

In coding, a toggle is typically a Boolean variable that is controlled by other variables, events, and actions in the program. The toggle can be flipped by the user or triggered by an event such as clicking a button. The state of the toggle is then reflected in the output generated by the program, whether it be an error message or an input value.

Savvy teams realize that each toggle configuration in the codebase has a carrying cost and seek to keep it as low as possible. To do this they are proactive about removing toggles that are no longer in use. For example, some teams put a toggle removal task on their backlog every time they release a feature flag and others add “expiration dates” to their toggles that will fail a test (or even refuse to start the application!) if not removed before the expiration date.