Feature flags for web apps — what to use

Feature flags are switches in code that toggle functionality without redeploy. Foundation tool for:

• Safer deploys (canary, gradual rollout).
• A/B testing.
• "Kill switch" for problematic features.
• Beta access for specific users.

Options:

• LaunchDarkly. Industry standard, mature. Expensive ($75+/seat/month for teams). Worth it for enterprises.
• GrowthBook. Open source, self-hostable. Free for most projects. Good A/B testing built in.
• PostHog flags. Bundled with PostHog analytics. Convenient if already on PostHog.
• Unleash. Open source, less polished, gets the job done.
• Custom. A flag table in your DB plus an admin UI. Built in a day. No A/B infrastructure out of the box.

Common mistakes:

• Flags that never get removed. Years later, dozens of dead toggles nobody remembers the purpose of.
• Flags read on every request without caching — slow.
• Flags by user_id not segment — can't roll out to "10% of users".
• No clear flag ownership — who decides when to remove the flag.