A toggle is a switch that can be set to either on or off. Feature toggles are used to change the state of features in software programs, enabling teams to experiment with features without impacting users. These switches can be used in a variety of ways, including to test new features on a small cohort of users, rollback bugs, and control access to premium features. Toggles can be configured with a variety of settings, but the most common configurations include boolean values and Boolean logic. Toggles can be a powerful tool for improving the quality of code and the user experience, but they should be deployed with care and only for the purpose for which they are designed.

Toggles are frequently used as part of responsive design in web development. They can be used to disable navigation menus or other components based on screen size and device type. They can also be used to show or hide different display options in a responsive interface.

Most toggles are short-lived, only staying active for a few days or weeks at most before being retired. This makes them perfect for testing a new feature with a limited audience before it goes live to the entire user base. However, in some cases, they may remain on for longer, such as when a company is experimenting with performance enhancements during high-latency periods.

Toggle can be used to support newer agile development models, allowing dev teams to work on new features that would normally have been written on separate code branches under waterfall development models. This allows teams to deploy features into production before they are complete, enabling them to meet delivery targets.

While there are many different approaches to creating and managing feature toggles, most involve a process of changing the state of a variable or a boolean logic decision by either deploying a change to production that includes the value for the flag or re-configuring the code with a preprocessor feature (such as #ifdef) that enables dynamic re-configuration of the toggle. There are some more sophisticated approaches to toggle configuration, but these can come at a cost of increased complexity.

A final use for toggles is to manage the exposure of premium features in apps that have a paywall. These can be enabled or disabled using a permission toggle depending on whether a user has upgraded their account. Permission toggles tend to be much longer lived than other categories of Feature Toggles, with the toggling decision often being made on a user-by-user basis. It is often debated whether or not a bug fix should be accompanied by a permission toggle, but I find it more reasonable to decide case-by-case if a toggle is needed rather than dogmatically creating one for every bug fix. This way the team can ensure that the toggle is only applied to users who need it, and that the toggle is withdrawn as soon as the feature has been fully rolled out to all users.