# Loose Coupling
In addition to the [robustness principle](core-principles/robustness.md), API consumers (clients) **MUST** **operate independently** on API implementation's internals. Similarly the API consumers **MUST NOT** **assume** or **rely on** any knowledge of the API service internal implementation. 

Where available, the clients **SHOULD** utilize **hypermedia controls as the engine of the application state**, and rely on the **protocol, message and vocabulary semantics**.