# Low Level Design
All Low Level Design notes →1 — Interface Design
Defines how a service's public surface is shaped so consumers depend on a stable contract rather than on internal implementation details.
2 — DTOs
Explains why data transfer objects decouple wire formats from domain models, so internal refactors don't ripple into API consumers.
3 — Validation Layers
Distinguishes syntactic, semantic, and business-rule validation so each concern is enforced at the layer best suited to catch it.
4 — Mapping Objects
Covers translating between domain models and DTOs at the API boundary without leaking persistence details or business logic across it.
5 — Pagination
Compares offset-based and cursor-based pagination strategies and how each behaves under concurrent writes and large result sets.
6 — Error Responses
Defines a consistent error response shape and status-code taxonomy so API consumers can handle failures programmatically rather than by parsing prose.