A toggle is a switch that can be used to select between two outcomes. In software a toggle can be applied to a piece of code, for example to turn a feature on or off. Toggles are commonly used in multivariate or A/B testing and can be a powerful tool for data-driven optimizations.

When designing toggles consider both user and societal impact. It is important to use high-contrast colors so that users can easily discern the state of a toggle. Additionally, it is important to avoid inversion of the toggle button, as this can cause confusion and result in users pressing the wrong side of the toggle.

Toggle configuration is typically managed via static files, however as the system scales these can be cumbersome to modify and maintain. For this reason, many teams choose to move their toggle configuration into some form of centralized storage such as an existing application DB. This can be paired with some type of admin UI that allows for dynamic in-memory re-configuration of individual toggles.

When creating toggles for production, it is wise to test both the current toggle configuration and a fallback configuration where all of the toggles you intend to release are flipped Off. This can help avoid unexpected regressions in the future. While this is a good practice it should be used sparingly and ideally as part of the automated testing suite. It is not a replacement for a robust distributed configuration system such as Secrets or Subscriber Containers.