What problem does it solve? Business logic often becomes entangled with frameworks, databases, and delivery mechanisms, making applications hard to test, resistant to infrastructure change, and fragile as frameworks evolve. This Skill guides the design of applications where the domain sits at the center and all dependencies point inward. ## Core Features & Use Cases - Layered Architecture Guidance: Defines the four layers (Entities, Use Cases, Interface Adapters, Frameworks & Drivers) and the Dependency Rule that keeps source dependencies pointing inward. - Ports and Adapters Design: Explains how to define application-owned ports (repository, email, clock interfaces) and implement technology-specific adapters, including driving vs driven port distinctions. - Testing Strategy: Maps the testing pyramid to architectural layers — pure domain unit tests, use-case tests with in-memory fakes, adapter tests against real technology, and minimal end-to-end tests. - Use Case: When building an order management service that must serve HTTP, message queue, and CLI clients, use this Skill to place business rules in a framework-free domain layer, define ports for persistence and notifications, and keep ASP.NET or Spring confined to the outer adapter layer. ## Quick Start Ask Claude to structure a new application or review an existing one against hexagonal and clean architecture principles, for example by requesting a ports-and-adapters design for a specific use case.
