---
name: feature-flag-system-bf56a8631fd4
description: >
  Implement feature flags (toggles) for controlled feature rollouts, A/B
  testing, canary deployments, and kill switches. Use when deploying new
  features gradually, testing in production, or managing feature lifecycles.
---

# Feature Flag System

## Table of Contents

- [Overview](#overview)
- [When to Use](#when-to-use)
- [Quick Start](#quick-start)
- [Reference Guides](#reference-guides)
- [Best Practices](#best-practices)

## Overview

Implement feature flags to decouple deployment from release, enable gradual rollouts, A/B testing, and provide emergency kill switches.

## When to Use

- Gradual feature rollouts
- A/B testing and experiments
- Canary deployments
- Beta features for specific users
- Emergency kill switches
- Trunk-based development
- Dark launching
- Operational flags (maintenance mode)
- User-specific features

## Quick Start

Minimal working example:

```typescript
interface FlagConfig {
  key: string;
  enabled: boolean;
  description: string;
  rules?: FlagRule[];
  variants?: FlagVariant[];
  createdAt: Date;
  updatedAt: Date;
}

interface FlagRule {
  type: "user" | "percentage" | "attribute" | "datetime";
  operator: "in" | "equals" | "contains" | "gt" | "lt" | "between";
  attribute?: string;
  values: any[];
}

interface FlagVariant {
  key: string;
  weight: number;
  value: any;
}

interface EvaluationContext {
  userId?: string;
// ... (see reference guides for full implementation)
```

## Reference Guides

Detailed implementations in the `references/` directory:

| Guide | Contents |
|---|---|
| [Feature Flag Service (TypeScript)](references/feature-flag-service-typescript.md) | Feature Flag Service (TypeScript) |
| [React Hook for Feature Flags](references/react-hook-for-feature-flags.md) | React Hook for Feature Flags |
| [Feature Flag with Analytics](references/feature-flag-with-analytics.md) | Feature Flag with Analytics |
| [LaunchDarkly-Style SDK](references/launchdarkly-style-sdk.md) | LaunchDarkly-Style SDK |
| [Admin UI for Feature Flags](references/admin-ui-for-feature-flags.md) | Admin UI for Feature Flags |

## Best Practices

### ✅ DO

- Use descriptive flag names
- Document flag purpose and lifecycle
- Implement gradual rollouts
- Track flag evaluations
- Clean up old flags regularly
- Use feature flags for experiments
- Implement kill switches for critical features
- Test both enabled and disabled states
- Use consistent hashing for stable rollouts
- Provide admin UI for non-technical users

### ❌ DON'T

- Use flags for permanent configuration
- Accumulate technical debt with old flags
- Skip flag cleanup
- Make flags too granular
- Hard-code flag checks everywhere
- Skip analytics and monitoring


---
Source attribution: aj-geddes
Original project: https://github.com/aj-geddes/useful-ai-prompts/blob/3f5182cfd739fc113f4af5244a1cf342ad7f7911/skills/feature-flag-system/SKILL.md
License: MIT
License information: https://opensource.org/license/mit
Original upstream instructions; downloaded from Mega AI Hub.

## Upstream license notice

MIT License

Copyright (c) 2025 AJ Geddes

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.


# Mega AI Hub resource metadata

Creator / publisher: aj-geddes
Original project: https://github.com/aj-geddes/useful-ai-prompts/blob/3f5182cfd739fc113f4af5244a1cf342ad7f7911/skills/feature-flag-system/SKILL.md
Attribution basis: Source repository record

Fields of work: Development & Engineering, Product Management
Roles: Backend Developer, DevOps / SRE, Product Manager
Specialties: Backend
Tools: Launchdarkly
Country applicability: Country not specified
Classification basis: Source catalog labels
Instruction SHA-256: 2e43a85d94a57ab6f0eb6f28f25fb9b103c474e766e8e3a2dcadd31a2725e5a2