Backend Basics
The backend is the server — the part your users never see. It runs the logic, enforces the rules, and guards the data behind everything the frontend shows.
What the Backend Does
Whatever the app, the server side keeps coming back to the same handful of jobs.
- Business logic — the rules of your app
- Auth — who is allowed to do what
- Talking to the database — reading and writing stored data
- Exposing an API — the endpoints the frontend calls
Request → Response
The backend receives a request, checks permissions, does the work, and returns data — usually as JSON.
You Can’t Trust the Browser
Anything sent to the browser, the user can change — the code, the data, every value client-side. So security, secrets, and the source of truth must live on the server, where the user cannot reach them.
Small, but Understood
A small backend can be a handful of endpoints. A coding agent can scaffold it for you in minutes — but you still need to understand auth and where secrets live, so you don’t ship something unsafe.
Build It
How to implement: list the 3–4 actions your tool needs the server to do — for example “add a task,” “list this week,” “summarize.” Those become your API endpoints.
- Weekly AI Tasks tracker — the backend holds the messaging webhook, the LLM calls, auth, and the database access. It is where the real logic lives.
- Personal brand site — a static site often needs no backend at all. Recognizing that saves cost and complexity (a Module 4 tradeoff).
What you learned
The backend runs the logic, handles auth, talks to the database, and exposes an API. It exists separately because the browser can’t be trusted — secrets and the source of truth belong on the server.