What is Feature Toggle? — UK Software Development Guide
Direct Answer
A feature toggle (also called a feature flag or feature switch) is a software pattern that allows features to be enabled or disabled without deploying new code. Feature toggles can be: release toggles (hide incomplete features in production), experiment toggles (A/B testing), ops toggles (emergency kill switches for problematic features), and permission toggles (different features for different user tiers).
Feature-toggle in the UK
Feature toggles are valuable for UK compliance and operational resilience. FCA operational resilience: a release toggle allows instant "rollback" of a new payment feature by toggling it off — without a code deployment. NHS zero-downtime: clinical feature toggles allow new clinical workflows to be tested with pilot users before full rollout. UK GDPR: consent-gated features (analytics, marketing automation) can be implemented as permission toggles controlled by user consent state — toggling features on/off based on the user's consent record. LaunchDarkly (enterprise, US company — requires GDPR DPA) and Unleash (open source, self-hostable — better for UK GDPR data residency) are the most common UK implementations.
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