Feature Flag

A feature flag is a runtime condition that turns behaviour on or off without deploying. Flags are what make Trunk-Based Development and Continuous Deployment practical: unfinished work can be merged and deployed while remaining inert.

Their uses divide into release flags (temporary, removed once a feature is fully out), operational flags (permanent kill switches), permission flags (entitlements), and experiment flags (A/B allocation). Conflating them is how flag systems become unmanageable, since only the first kind should ever be deleted and only the last needs analytics.

Two implementation notes matter more than the mechanism.

Gate at the narrowest point that is actually load-bearing. If every affordance for a feature hangs off one component, one condition covers all of them. But hiding the interface is not sufficient — the write path must be gated too, or the capability is merely undiscoverable.

Verify the off state positively. An absent element is indistinguishable from a page that failed to load. Confirming that the surrounding interface is present on the same load is what makes "the flag is off" a real observation rather than an inference.

Flags accumulate. A flag whose feature has fully shipped is dead conditional logic in every path it touches, and removing it is real work that has to be scheduled.