Provides a structural guideline for organizing codebases so that business logic remains independent of external concerns such as UI, databases, and frameworks.

To communicate a layered architectural approach that enforces dependency direction toward the core domain, facilitating maintainability and testability.

When designing a new software system or refactoring an existing one to achieve loose coupling, testability, and independence from frameworks or infrastructure concerns.

Software architecture discussions, layered architecture discussions, domain-driven design, clean architecture conversations, enterprise application design.

Concentric layers: Infrastructure → Application Core → Domain Entities (inner) → Interfaces → Frameworks/Drivers (outer).

Entities → Use Cases → Interface Adapters → Frameworks & Drivers.

• clean architecture
• hexagonal architecture
• ports and adapters
• domain-driven design
• separation of concerns
• dependency inversion

• clean architecture
• hexagonal architecture
• ports and adapters

Allowing outer layers to reference inner layers incorrectly, leaking domain entities to outer layers, letting infrastructure concerns leak into domain layer.

Layered architecture (traditional layered), MVC, MVVM, traditional 3-layer architecture

Confusing onion architecture with traditional layered architecture where dependencies flow inward and outward; mixing concerns across layers.

• Software architecture patterns
• Layered architecture
• Domain-driven design

Emphasizes dependency rule: inner layers cannot know about outer layers; all dependencies point inward.

Encourages teams to think about boundaries and maintainability, leading to more adaptable and testable codebases.

Think of an onion: core at the center, layers wrapping outward, each depending only on the layer beneath.

Often used interchangeably with clean architecture and hexagonal architecture, though subtle differences exist.

Clean architecture / Hexagonal architecture