A toggle is a piece of hardware or software that allows the user to switch between two functions. For example the Caps Lock and Num Lock buttons on a keyboard are toggles that enable or disable specific functions. Similarly toggles are also used in software and can be found for example in options menus. A toggle switch can be turned on or off with a single click and is usually displayed with a light showing which state it is in.

Good toggles use high contrast colors to clearly signal their state. They also have clear and direct labels indicating what each option does. The label should also be able to be understood by a wide range of users with different visual abilities and should be adapted for cultural differences.

Toggle design should also consider the societal and cultural implications of colors for toggles as these can influence how they are perceived. For example using red for toggles can be counterintuitive to people who associate this color with stop signs and traffic lights. Embossment can be another visual cue for toggles but it should be combined with a primary cue such as color or font size and shouldn’t be used alone.

When using toggles for feature flags it’s important to make sure that you have a robust runtime configuration system that allows for the dynamic re-configuration of service instances. This can avoid the need to restart a service in order to flip a toggle and will allow for a faster feedback loop within your development process. It’s also important to test all the toggle configurations that you plan on releasing in production including any that have been flipped On. It’s often useful to also test a fallback configuration that has all toggles flipped Off.