Build a Feature Flag System
Implement a feature flag system with user targeting, gradual rollout, and A/B testing support.
The Prompt
Build a lightweight feature flag system with these capabilities: 1. Boolean flags (on/off for all users) 2. User-targeting flags (enabled for specific user IDs or emails) 3. Percentage rollout (e.g., enabled for 20% of users, deterministic by user ID) 4. Environment overrides (always on in dev, controlled in prod) 5. A/B test variants (assign users to named variants) 6. Flag evaluation logging for analytics Provide: - The flag configuration schema - Flag evaluation function - React hook for client-side usage - Server-side usage example Stack: TypeScript, Next.js. Use [UPSTASH REDIS / LOCAL JSON FILE — specify] as the config store.
Example Output
Built a type-safe feature flag system with a JSON schema for flag definitions, a deterministic hash-based percentage rollout (user ID → consistent bucket), a useFlag() React hook that reads from a context provider, and a server-side getFlag() that reads from Upstash Redis with 60-second caching.
FAQ
Which AI model is best for Build a Feature Flag System?
Claude Sonnet 4 — strong at system design with TypeScript types.
How do I use the Build a Feature Flag System prompt?
Copy the prompt, replace the [BRACKETED] placeholders with your specific information, and paste into your preferred AI assistant (ChatGPT, Claude, Gemini, etc.). Built a type-safe feature flag system with a JSON schema for flag definitions, a deterministic hash-based percentage rollout (user ID → consistent bucket), a useFlag() React hook that reads from a context provider, and a server-side getFlag() that reads from Upstash Redis with 60-second caching.
Model Recommendation
Claude Sonnet 4 — strong at system design with TypeScript types.