A toggle is a switch that can be activated to change between two states or options. This simple concept is applied widely in technology, computing, programming and user interfaces. For example, keyboard keys like Caps Lock and Num Lock are toggles that allow users to toggle various functions on or off.

In a software context, feature toggles are used for A/B testing and act as circuit breakers. They bucket users into groups and when a new feature is toggled ON, those users experience the new functionality. When the toggle is turned OFF, those same users see the original version of the application without the tested feature. This allows engineering teams to validate features with a small segment of their audience before they roll them out to everyone.

For many products, toggles are also useful for managing access to features based on a user’s membership level. This is done by setting the toggle state to a value that corresponds with a specific user role. For example, if a user upgrades to Premium, the toggle is set to turn ON premium features for that user. This allows the product team to validate that the new features are adding value for their paying customers before deploying them to all users.

One challenge with toggles is that they require a certain amount of technical sophistication to be implemented and managed. Most organizations move their toggle configuration away from static files and into some type of centralized storage, often an existing application DB. This makes them more accessible to developers, testers and product managers. Some even create an admin UI to make it easy for people to view, modify and manage feature flags and their configuration.