How do you determine whether functionality belongs to the frontend or backend in system architecture?

Frontend is the part of the system that interacts directly with the user, usually the interface: web pages, mobile applications, client programs. Backend is the server-side part that processes logic, stores data, performs calculations, and responds to frontend requests.

Features of the frontend:

• Rendering the interface and interacting with the user.
• Handling user events (clicks, input).
• Sending requests to the server.

Features of the backend:

• Processing business logic.
• Working with databases.
• Authentication and authorization.
• Processing and forming data for the frontend.

For example, in a web application, a button and a form are frontend, and the server that receives form data and saves it to the database is backend.