A toggle is a switch with two positions — on and off. It can also be used to refer to switching back and forth between settings or programs, such as when you use Alt+Tab to toggle between Microsoft Excel and the calculator while working on a spreadsheet.

In software development, toggles are used to enable features for a limited number of users, or to test the effects of an update on the entire user base. Toggles can be implemented on both existing features and new ones, allowing the engineering team to quickly roll out features for testing, while minimizing risk and enabling the feedback loop needed for continuous improvement.

The most common use of toggles is for A/B testing. Toggles bucket your users into groups and at runtime the feature toggle will send a given user down one codepath or another based on which group they are in.

Savvy teams view Feature Toggles as inventory that comes with a carrying cost. To this end, most teams will be proactive about removing toggles from their codebase when they are no longer necessary. Some teams will even add a task to the backlog whenever a toggle is first introduced, while others go as far as setting “expiration dates” for their toggles and putting time bombs into their tests that will cause them to fail if a toggle is still active after its expiration date.

When designing a toggle it’s important to make sure that it’s easily readable for all your users, especially those with accessibility needs. Often, toggles are purely visual and rely on color changes to communicate whether a feature is enabled or disabled. This can be problematic for people with vision impairments, such as those who have red/green color blindness. As such, designers should be thoughtful about their choice of visual cues to ensure that they are accessible.