A toggle is a control that has an initial state of off, and then when clicked changes to the on state. Toggles are used in software and hardware, for example the caps lock and num lock keys on keyboards are toggles that initially turn off, then when pressed turn on. Toggles are also found in options menus in software applications.

Toggles are most often seen as a form of user interface element, though they can be found on other types of elements such as buttons. Toggles are a very powerful tool for developers and designers, but like all tools can be misused or misunderstood. They should only be applied when they provide immediate results and no other type of user input is required for the change to take effect (for instance a Save or Submit button). If these conditions are not met then another form of user interaction such as a checkbox or radio button may be a better choice.

Feature Toggles can be implemented in a number of ways, ranging from very simple approaches that are less dynamic through to more complex and sophisticated solutions. The latter generally involve storing the feature flag configuration in a centralized store, such as an existing application DB or an external service that can manage these features.

The use of a centralized store for feature flags can help to avoid some of the issues that are associated with using static files, especially at scale. It can also make it easier to manage the varying state of Toggle switches across a fleet of servers and ensure consistency within a deployment environment.

It can be difficult to write toggles that are easy for users to understand and interpret. For this reason it is important to focus on good naming and labeling. A toggle switch should be given a name that clearly describes its purpose and what state it is currently in. It should also be labelled with an icon that is easily recognisable as being a toggle and which will allow the user to instantly determine the status of the switch.

A toggle can be configured to act upon a variety of different things, these can range from fitness test results to a set of predefined values defined in an admin UI. A toggle can also be configured to respond to different events such as a call to action button click or the completion of a purchase in an ecommerce system.

Using toggles to perform multivariate or A/B testing can be a powerful way for teams to gain data-driven insight into which features work best for their users. For example, an ecommerce company that is debating which of two suggestion algorithms will provide the best conversion rate can create an experiment toggle and deploy it to live traffic. Once they have conclusive evidence that the algorithm with a higher conversion rate is performing better they can remove the experiment toggle and implement that algorithm in production.