A toggle is a switch that has two positions, on and off. It’s a common user interface element found in options menus, and most hardware such as the keyboard’s Caps Lock and Num Lock keys, which are toggle switches that enable specific functions that otherwise wouldn’t be enabled. Toggle is also a verb that means to alternate between two things, such as switching between video screens while talking with friends over video chat.

Toggles can be used to perform multivariate testing (or A/B testing) by enabling and disabling codepaths for different cohorts of users. This allows us to measure the aggregate impact of different features and then make data-driven optimizations.

The most important consideration when designing and implementing toggles is to be clear in their labeling. Toggle labels should indicate what they will do when flipped, be high contrast and utilize visual signifiers. It’s also best practice to use standardized toggle icons and ensure that the state of each toggle can be easily discerned through its appearance.

When a toggle is flipped on it should be clearly indicated through a change in color and the use of the word On or Off. This is especially important for older users who may not be familiar with the meaning of the word toggle or its meaning in other contexts.

At scale, the ability to dynamically re-configure specific service instances via a toggle can be invaluable. For this reason, it’s often desirable to move away from static toggle configurations that live side-by-side in files and towards a more robust and distributed configuration system which supports runtime re-configuration.