What are Feature Flags
Feature Flags (feature toggles) — mechanism for turning features on/off at runtime without deploy. Code: if (flags.isEnabled("new-checkout")) { ... }. Enables: gradual rollout, A/B testing, kill switch for broken features, targeted release (beta users only, RU segment). Tools: LaunchDarkly ($), GrowthBook (open-source), Unleash, ConfigCat, build-your-own feature service.
Below: details, example, related terms, FAQ.
Details
- Release flags: progressive rollout %
- Experiment flags: A/B test 50/50
- Kill switch: emergency disable a feature
- Permission flags: user/tenant-based access
- Ops flags: on/off for infrastructure (circuit breaker)
Example
// LaunchDarkly example
import { LDClient } from 'launchdarkly-node-server-sdk'
const ld = LDClient.init(sdkKey)
if (await ld.variation('new-checkout', user, false)) {
return renderNewCheckout()
}Related Terms
How to Implement Feature Flags in Your Codebase
Best Practices for Using Feature Flags
Common Use Cases for Feature Flags
Learn more
Frequently Asked Questions
Why need if we have canary?
Canary — deploy-time gradual. Feature flags — runtime toggle. Flags live longer (weeks): progressive rollout + experiments + kill switch.
Feature-flag debt — a problem?
Yes. Old flags clutter code. Best practice: TTL on a flag, auto-reminder in PR review after 30 days.
Open-source tools?
GrowthBook (free + paid), Unleash (free for 1 project), Flipt. LaunchDarkly — premium SaaS.
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