Frontend and Backend: What's the Difference?
Every web application has two distinct parts that work together: the frontend and the backend. Understanding where each runs and what each does is essential for building anything on the web.
Where Code Runs
The frontend is everything that runs in the user's browser or on their device. When you visit a website, your browser downloads HTML, CSS, and JavaScript files. Those files execute on your computer, rendering what you see and responding to your clicks.
The backend runs on a server somewhere else entirely — a computer in a data center that you never see. It handles data storage, business logic, and anything that shouldn't happen on the user's device.
These two parts communicate over the network using HTTP requests and responses. The frontend asks for things, the backend responds.
The Restaurant Analogy
Think of a restaurant. The dining room is the frontend — it's where customers sit, read menus, and enjoy their meals. The kitchen is the backend — it's where food gets prepared, ingredients are stored, and recipes are followed.
The waiter carries requests from dining room to kitchen and brings responses back. That's exactly what HTTP does between frontend and backend.
What Each Side Handles
Frontend responsibilities:
- Displaying information to users
- Collecting user input (forms, clicks, typing)
- Making the interface look good and feel responsive
- Sending requests to the backend
Backend responsibilities:
- Storing and retrieving data from databases
- Processing business logic (calculations, validations)
- Authenticating users and protecting data
- Sending responses to the frontend
Why the Separation Exists
You might wonder why we don't just do everything in one place. The separation exists for security and capability reasons.
Users can inspect and modify frontend code — it runs on their machine. Anything sensitive (passwords, payment processing, private data) must happen on the backend where users can't tamper with it.
Backends also have capabilities browsers don't: direct database access, file system operations, and connections to other services.
The Same Concepts Everywhere
Whether you use React or Vue for frontend, Python or Node.js for backend, the fundamental split remains identical. Frontend code runs on the client, backend code runs on the server, and they talk over HTTP.