Feature Flag

What is Feature Flag?

A feature flag (or feature toggle) is a conditional piece of code that allows you to turn features on or off in production without releasing a new version. For example, a flag might show a new dashboard only to 10% of users, or hide a broken feature immediately if problems emerge. Flags can be toggled on/off globally, per user, per region, or based on any custom criteria.

Why It Matters

Feature flags let you deploy incomplete work to production safely. You can test features with real data and real users without risking widespread breakage. They also eliminate the 'I shipped a bug, now I have to roll back everything' problem—instead you flip a switch and the problem disappears. For teams shipping fast, feature flags transform deployment from an event you fear into a routine action.

How to Apply

Implement flags around risky features, incomplete work, and experimental changes. Use a feature flag service like LaunchDarkly or build a simple internal system. Deploy your feature behind a flag, test thoroughly with a small percentage of traffic, monitor metrics, and gradually increase rollout. If something breaks, disable the flag immediately—no emergency hotfix, no rollback required. Use flags for A/B tests, beta features, and gradual rollouts.

Common Mistakes

• Using feature flags as a substitute for proper testing—flags are a deployment tool, not a testing tool
• Leaving old flags in code indefinitely—clean them up once a feature is fully launched or permanently removed
• Toggling flags based on assumptions instead of metrics—'I think users like this' is not data

Related Terms