A toggle is a switch that has two positions: on and off. It is often found on computers and other machines where it is used to enable or disable functions, like a screen sharing feature when video chatting with friends.

When talking about software, a toggle is a feature that allows teams to roll out new features in a controlled manner. Feature toggles allow teams to test and experiment with software updates before committing to the full release, reducing the risks associated with live releases.

Feature toggles can be used for a variety of purposes, from testing to phased rollouts and targeted user groups. This flexibility makes them a powerful tool for agile development processes, allowing teams to gather real-time feedback from users while also paving the way for continuous improvement.

While Feature Toggles can provide significant benefits they can also pose challenges. Feature toggles can increase the number of configuration options, requiring teams to create additional unit tests in order to cover all possible combinations of settings. Using toggles can also require teams to perform double testing when a feature is deployed, since they will need to run their tests with the toggle both disabled and enabled. Savvy teams avoid these problems by keeping a limited amount of inventory under their control at any given time and being proactive in removing toggles when they are no longer needed. Some teams have even gone so far as to put “expiration dates” on their toggles, making it difficult for a feature to remain in the codebase after its initial rollout.

In general, the most effective use of toggles is to use them for features that are highly dependent on each other. This will help reduce the need for duplication of code and ensure that all unit tests have a complete picture of the system state.

Another important thing to keep in mind when using toggles is the need for a clear and consistent design language. Because toggles are visible to all users, it is important that they be readable and understandable. This can be accomplished by maintaining a consistent design style and using clear labels for each toggle.

The last thing to keep in mind is the need for a clear separation between the code that determines whether a toggle is on or off and the user interface. This will make it easier to debug and troubleshoot if problems arise. Fortunately, this is not as challenging as it may seem. For example, many companies create a new branch of their codebase to support a new feature and then generate a Release Toggle to disable it until they are ready to deploy it to production.

Other companies, such as Etsy, use Feature Toggles to perform continuous deployment. They create a feature in their main codebase and then hide it behind a release toggle, allowing them to gradually expose the feature to a small group of users while monitoring performance and gathering feedback. When a feature is ready for broader exposure it can be merged into the master codebase and enabled with a single toggle change.