A toggle is a switch that has two positions: on and off. It’s used in software and hardware to turn features on or off. A common example is the Caps Lock or Num Lock key on a keyboard. In software it’s used in options menus where a checkbox can be toggled on or off. A toggle can also be a piece of metal or other material that is passed transversely through a hole or loop in a chain, rope, etc., as to bind it temporarily. The word is derived from the English verb toggle, meaning “to pass transversely through.”
In a user interface it’s important for users to understand how to use toggle switches. They should be clearly labeled and positioned within an accessible area of the screen. It’s also helpful to use visual cues, such as movement and color, to indicate when a toggle is changing states.
It’s also important to be able to test the toggles in your application. This can be accomplished through a variety of means from simple commenting to leveraging preprocessor features, such as #ifdef, to dynamically re-configure service instances. While these methods are useful they can have a significant impact on the cycle time of your testing and validation process, especially when working with Experiment Toggles or other toggles that may need to be re-deployed multiple times during an experiment.
Savvy teams view their Feature Toggles as inventory that comes with a carrying cost and seek to keep the amount of toggles in their codebase to a minimum. Toggle removal tasks are frequently added to a team’s backlogs and some teams even put “expiration dates” on their toggles.