featuretoggle

Feature toggle, also known as a feature flag, is a software development technique that allows enabling or disabling a feature at runtime without deploying new code. A toggle is a conditional check in the application that determines whether the feature’s code path should execute. Flags may be controlled via in-code configuration, environment variables, or a dedicated feature flag management service, enabling dynamic behavior changes without a redeploy.

Purposes of feature toggles include releasing features gradually (canary or staged rollouts), providing safe kill switches, enabling A/B testing, and delivering targeted experiences for specific users, environments, or teams. They support rapid experimentation, risk reduction, and smoother rollout processes, while allowing teams to revert changes quickly if issues arise.

Tactical classifications commonly used are release toggles, experiment toggles, and ops toggles. Release toggles enable a feature to be turned on for testing or gradual exposure; experiment toggles route some users to a variant for measurement; ops toggles provide emergency disablement. Flags can also be user-targeted or environment-specific.

Implementation approaches vary from in-code boolean checks to external flag services that offer dashboards, targeting rules, auditing, and real-time updates. Flags can be persistent or short-lived; temporary toggles should be removed once the feature is fully released and stable.

Best practices include keeping toggles small and well-scoped, documenting purpose and ownership, and testing both states (on and off). Monitor usage and performance, plan for removal to avoid flag debt, and manage governance to prevent flag sprawl. Consider security and reliability when flags reveal or gate sensitive functionality, and ensure fallbacks are robust.