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Layered architecture separates application concerns into distinct layers with clear responsibilities: domain models define business constraints, application layer orchestrates workflows, repositories handle persistence, infrastructure provides external integrations, and interfaces serve as entry points. Dependencies flow inward, keeping business logic independent of frameworks and databases. For larger systems, vertical slicing by domain prevents layers from becoming dumping grounds. This structure reduces cognitive load, improves testability, and makes changes safer and cheaper over time by allowing extension rather than rewriting.

Layered Architecture for Building Readable, Robust, and Extensible Apps

Larger apps: Horizontal layering per domain boundary

Practical example: refactoring a real endpoint