A toggle is a switch that has two positions, either on or off. It is also a verb meaning to move between one state and another such as when you toggle between screens as you video chat with two friends at once. It is important to understand how toggles work as they are a commonly used user interface component in web applications and mobile devices.

In software development a toggle is a way to enable/disable functionality that allows for a very fast feedback loop with users. By enabling features in a controlled manner and then quickly collecting data on how those features are used teams can make informed decisions about when to move a feature into production.

There are a few different types of toggles:

Feature Toggle

This is the most common type of toggle and it allows a team to enable/disable functionality with a single line of code. This can be used to enable/disable anything from new functionality to bugfixes. This type of toggle is very useful in the QA/Testing process as it provides a way to easily disable functionality that would break a test without needing to re-deploy a full application image.

Experiment Toggle

This type of toggle is typically used for things like multivariate or A/B testing where a given user will be sent down one of several different codepaths. The results from the experiment can then be compared and the best path implemented in production. This type of toggle is also great for testing things such as the impact of an icon redesign or other visual changes that may not have a large impact on a majority of users.

Toggle Configuration

For larger scale use cases it can be helpful to store toggle configuration in some form of centralized location. This can help ensure consistency across a fleet of servers and makes it easier for developers, testers and product managers to view and modify feature flags as needed. Using static files for this purpose can be cumbersome at scale and many organizations prefer to implement a more scalable solution such as an existing application DB or a dedicated feature flag management system.

Savvy teams realize that the inventory of toggles in their codebase has a carrying cost and should always be proactive in removing toggles once they are no longer required. This helps to keep the overall number of toggles low and also avoids unnecessary regressions for users. To help mitigate the risk of these regressions it is often wise to perform some tests with all feature toggles flipped On and some with all feature toggles flipped Off. This allows teams to catch regressions that are hidden when a toggle is only flipped On. This can be especially beneficial for Canary Releases and other types of Continuous Integration workflows.