A toggle is a switch that allows you to turn something on or off. It’s an easy-to-use interface element that can be found in many places, such as computer settings or phone apps. Toggles are a great choice for changing system settings because they take up less screen estate than a radio button and have a pre-selected default state (either ON or OFF). They’re also a good choice on mobile devices because users often only have limited screen space to work with.

The term “toggle” is often used as a verb to mean switching between settings or programs: “She toggled between the baseball game and the news.” Toggles are also commonly used in product testing and experimentation, especially to perform multivariate or A/B tests. This type of testing requires that a large number of users be divided into two or more cohorts and the toggling decision for each cohort to send them down one codepath or another is made at runtime.

Toggle configuration is typically handled in some form of centralized config store. This is most frequently done in the form of an existing application DB where administrators, testers and product managers can easily modify the config for specific service instances. The use of static files is fraught with issues though as changes must be manually applied and rolled out across a fleet of servers — slowing down the cycle time for validating and optimizing a feature flag.