Feature Flags 101: A Practical Guide for Modern Development

Feature flags have transformed how modern teams ship software. In this guide, we'll cover everything from the fundamentals to production-ready patterns.

What Are Feature Flags?

Feature flags are configuration switches that let you enable or disable features without deploying code. Think of them as light switches for your application's features.

if (isEnabled('new-checkout')) {
  return 
}
return 

Why Use Feature Flags?

Feature flags solve several critical problems in software delivery:

1. Decouple Deployment from Release

Deploy code safely to production with features turned off. Enable them when you're ready. This means you can deploy at 2 PM on Friday without fear.

2. Gradual Rollouts

Release features to 10% of users first. Monitor metrics. If everything looks good, roll out to everyone. If not, disable instantly.

3. A/B Testing

Show different features to different user groups. Measure which performs better. Make data-driven decisions.

4. Emergency Kill Switch

When something breaks in production, disable the feature in seconds. No deployment, no waiting, no downtime.

Types of Feature Flags

Release Flags

Short-lived flags for new features. Remove after full rollout.

// Release flag - remove after rollout
if (flags.isEnabled('redesigned-dashboard')) {
  return 
}

Operational Flags

Control system behavior in production. Often permanent.

// Operational flag - keep long-term
const enableCaching = flags.isEnabled('enable-redis-cache')
if (enableCaching) {
  return await cache.get(key)
}

Experiment Flags

For A/B tests and experiments. Remove after experiment concludes.

Permission Flags

Control access to features based on user role or subscription.

Best Practices

Naming Conventions

Use descriptive, kebab-case names:

• ✅ new-payment-processor
• ✅ enable-dark-mode
• ❌ feature1
• ❌ test_flag

Flag Lifecycle

1. Create: Add flag with clear purpose
2. Test: Verify in staging environment
3. Deploy: Ship to production (flag OFF)
4. Enable: Gradually roll out
5. Monitor: Watch metrics closely
6. Remove: Clean up code after full rollout

Getting Started with FlagSwift

FlagSwift makes feature flags simple:

// 1. Install
npm install @flagswift/react-client

// 2. Initialize
import { FlagProvider, FlagClient } from '@flagswift/react-client'

const client = new FlagClient({
  apiKey: process.env.NEXT_PUBLIC_FLAGSWIFT_API_KEY,
  environment: 'production'
})

// 3. Use flags
import { useFlag } from '@flagswift/react-client'

function MyFeature() {
  const enabled = useFlag('my-feature')
  return enabled ?  : 
}

Conclusion

Feature flags are essential for modern software delivery. They enable safe deployments, gradual rollouts, and instant rollbacks. Start small, follow best practices, and clean up regularly.