A toggle is a switch that allows you to easily change between two states or options. They’re commonly used in technology, computing, programming, and communication to give users control over different settings or modes. When a toggle is turned on, it changes to one state, and when it’s off, it switches to another.

Toggles can be very useful for multivariate (A/B) testing and improving user experience. A common example is an e-commerce company trying to determine which of two suggestion algorithms provides the best customer experience. They add an experiment toggle to their production configurator and split their users into cohorts, which then load the configurator with either the A or B algorithm. They watch the behavior of each cohort to see which version drives more conversions. Once they’re confident which algorithm is better, they remove the experiment toggle and go live with that version.

As with all design elements, it’s important to maintain consistency when using toggles in your application. Use high-contrast colors and provide clear visual cues when a toggle’s state changes. Also consider societal and cultural context when choosing colors, as they can have very different meanings for users.

Keeping the number of feature toggles to a minimum is also key. A large inventory of toggles can create a cognitive overhead for testers as they review which artifacts are enabled and which aren’t. Savvy teams often create a process for vetting and removing feature toggles when they’re no longer needed, and some even set up time bombs that will fail a test run if an idle toggle remains in the codebase after its expiration date.