What is a feature toggle?

A feature toggle, also known as a feature flag or switch, is a code-level tool that allows developers to enable or disable functionality at runtime without deploying new code. This approach enables the separation of feature activation from code deployment, allowing developers to modify application behavior by adjusting configurations in a feature flag system. Various toggle types exist to suit different needs, such as release toggles for trunk-based development, experiment toggles for A/B testing, operational toggles for runtime adjustments, and permission toggles for controlling user access to premium features. Feature toggles offer advantages over feature branches by allowing incomplete code to live in the main branch while managing complexity through conditional logic. Activation strategies determine which users see specific features, supporting controlled rollouts and user-targeted deployments. Effective management of toggle lifecycles is crucial to prevent technical debt, with practices such as automated cleanup and monitoring helping to maintain a clean codebase. Feature toggles differ from configuration settings by specifically managing feature availability and are designed to be temporary, with minimal impact on application performance.