A toggle is a type of control used to enable and disable software features. Usually toggles are presented to users as buttons that have two mutually exclusive states (such as ON and OFF). When a button is pressed, it toggles the state between the two states. This is similar to the way that a switch operates.

Toggles are commonly found in user interfaces to allow users to update their preferences or settings. It is important that designers use them correctly by ensuring that they are clearly labeled, consistent in visual design, and deliver immediate results when pressed. In addition, designers should evaluate the societal and cultural implications of using colors to signal toggle states. For example, using red to indicate that something is on may be counterintuitive to some people due to a negative connotation associated with the color.

The best way to make sure that a toggle is properly configured is to ensure that it’s encapsulated in some form of runtime configuration. A simple approach would be to hardcode the toggle into a static file or use a preprocessor’s #ifdef feature. However, this approach can become cumbersome at scale and makes it difficult to manage in a CI/CD environment. A more sophisticated approach is to store the toggle configuration in a centralized location, often a dedicated app DB. However, this can also be a complicated proposition and requires that teams create a management interface to allow product managers, testers, and other stakeholders to modify toggle configuration.

It is generally best to avoid relying on a toggle in cases where the system needs to be highly responsive or where the behavior of the application could change unexpectedly based on the state of the toggle. For instance, it is a good idea to avoid using toggles to hide email messages when the system needs to respond quickly to incoming requests. Instead, it’s more appropriate to use a checkbox or another control that isn’t susceptible to toggle changes.

When developing a new feature it’s always wise to test the toggle configuration that is expected to go live in production. This includes testing the existing behavior of a product with the toggle flipped off as well as testing the new behavior when the toggle is flipped on. In addition, it’s important to test the fallback configuration where the toggle is flipped off since this will be the default behavior for most users.

One of the biggest advantages of using a toggle to manage a feature flag is that it allows for more complex operations such as a Champagne Brunch or multivariate testing. In these types of experiments the toggle will consistently send a cohort of users down one code path or the other, allowing teams to track and compare the performance of each over time. However, this type of feature toggling will require that we deploy our code frequently and is therefore a poor choice for the rapid iteration required by CI/CD.