Context

Mobile apps rarely work in isolation. Most production apps at companies like Spotify or Uber rely on backend services for authentication, user data, content, and business logic.

Core Question

Explain the role of REST APIs in mobile apps. In your answer, address these points:

1. What a REST API is and why mobile apps use it.
2. How a mobile client communicates with a REST service using HTTP methods, endpoints, headers, and JSON.
3. What responsibilities should stay on the mobile app versus the backend.
4. Common concerns such as authentication, caching, pagination, errors, and versioning.

Scope Guidance

The interviewer expects a practical systems explanation rather than protocol trivia. You should describe how REST fits into a typical mobile architecture, what benefits it provides, and what trade-offs or limitations engineers should understand when building or consuming these APIs.