Toggle () is a form of on/off control found in hardware, systems and software settings. It’s the same concept behind keyboard keys like Caps Lock and Num Lock, allowing the user to toggle between different functions in their system.

When designing an interface with Toggle the most important consideration is ensuring the toggle is recognizable in its current state. It should be a clear visual signifier of the state and utilize movement and color to reinforce that it can be changed. The button> element can be used to markup a Toggle but in some cases, it might be better suited as an input> with the aria-pressed attribute. For example, if the toggle controls an instantaneous action then a button might be more appropriate as it can trigger a click event.

In addition to visual cues it’s also important for designers to think about the underlying semantics of a toggle. It’s generally best to set a convention of having existing or legacy behavior enabled when a toggle is flipped On and new or future behavior enabled when a toggle is flipped Off. This will help to avoid confusion for users and ensure they are testing against a known state of a feature.

As mentioned above, managing toggle configuration via static files can become cumbersome as a team grows and requires the use of a tool like Git to manage changes across multiple servers. To address this many organizations opt to move their toggle configuration into some type of centralized store, usually an existing application DB. This will often be accompanied by the build-out of some kind of admin UI which allows for system operators, testers and product managers to view and modify Features Flags and their configuration.