What is backend?
Backend is the trusted part the user cannot see — it runs logic and talks to the database.
Mental model
Plain English
The backend lives on a server you control. It checks permissions, runs business logic, reads and writes the database, and returns clean results to the frontend. Anything secret or risky belongs here.
The backend is the kitchen: it has the fridge, the recipes, and the chef. The customer never enters.
When a planner clicks 'Send vendor email', a backend function checks they're on the team, fetches the vendor, and triggers the email.
When a WhatsApp message arrives, the backend writes it to the database and pushes it to the inbox in realtime.
Go deeper
The trusted, hidden part of the app.
Common mistakes
- Letting the frontend do permission checks. Always re-check on the backend.
- Returning raw database rows that include other users' fields.
AI-agent trap
Summary
Backend code runs on a server (or serverless function). It receives requests, validates them, reads or writes data, and returns a response.