Backend principles

Much more or less the Backend Checklist note but this is like the condensed version.

1. CORS

— First thing you hit when React tries to talk to Flask.
Controls which origins can access your API.

2. Error Handling

— Centralised error responses. Instead of scattered
return {"error": ...} everywhere, one place handles
all errors consistently.

3. Input Validation

— Validate data before it touches your DB.
Wrong types, missing fields, bad formats — caught early.
Tools: Marshmallow, Pydantic, or manual checks.

4. Pagination

— Don't return 10,000 rows at once. Return page 1 of 20,
let the client ask for more. Needed as soon as your
DB grows beyond toy data.

5. Rate Limiting

— Limit how many requests a client can make in a time window.
Protects against abuse and brute force attacks.
Tool: flask-limiter.

6. Swagger / API Documentation

— Auto-generate interactive docs from your code.
Employers, teammates, and your future self will thank you.
Tool: flask-smorest or flasgger.

7. Caching

— Store expensive query results temporarily so you don't
hit the DB on every request. Needs Redis.
Tool: flask-caching + Redis.

8. Celery

— Run tasks in the background (sending emails, processing
images, scheduled jobs) without blocking the request.
Needs Redis or RabbitMQ as a message broker.