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What Are Feature Flags

Feature Flags vs. Config Toggles: What’s the Difference?

Not all toggles are equal. Understand when to use runtime flags vs. static configs for safe changes.

10 min read
FeatureFuse Team

Flags are dynamic and targeted; configs are static. Each has a place.

Evaluation Timing

  • Build-time
  • Startup-time
  • Request-time

Risk Surface

  • Blast radius
  • Rollback time
  • Observability

When to Use Flags vs Config

  • User‑facing behavior changes → flags
  • Static infra values → config
  • Emergency toggles → flags

Targeting & Segments

  • Internal users
  • Beta cohorts
  • Regions & plans
  • Device classes

Checklist & FAQ

  • Typed accessors in code
  • Single source of truth for flag definitions
  • Owner and removal date tracked
  • FAQ: Can flags replace env vars? Use flags for runtime targeting; env vars for static config.

Conclusion

Use flags when behavior must change by user or cohort without redeploys; use config for static settings.

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