Main Categories of Status Codes

1. 2xx → Success

Everything worked as expected

• 200 OK → Request successful
• 201 Created → Resource created

Example:
You request user data → Server sends data → 200 OK

2. 4xx → Client Errors

Problem from user/client side

• 400 Bad Request → Invalid input
• 401 Unauthorized → Not logged in
• 403 Forbidden → No permission
• 404 Not Found → Resource doesn’t exist

Example:
Searching for a user that doesn’t exist → 404 Not Found

3. 5xx → Server Errors

Problem from server side

• 500 Internal Server Error → General failure
• 502 Bad Gateway → Server received invalid response
• 503 Service Unavailable → Server down/overloaded

Example:
Server crashes while processing → 500 Internal Server Error

Why Status Codes Matter

• Help developers quickly identify problems
• Improve debugging speed
• Make APIs standard and predictable

Without status codes, every response would feel like:
"Something happened… but we don’t know what."

Real-Life Examples

1. Online Shopping (Client Error – 400 Bad Request)

You try to place an order but forget to enter your address.

• System response: “Address field is required”
• What happened? → You gave incomplete input

API Meaning:
Client sent wrong/insufficient data → 400 Bad Request

2. Login Attempt (Client Error – 401 Unauthorized)

You enter the wrong password while logging in.

• System response: “Invalid username or password”
• What happened? → Authentication failed

API Meaning:
User is not verified → 401 Unauthorized

3. Server Crash While Booking (Server Error – 500 Internal Server Error)

You try booking a movie ticket, but the server crashes.

• System response: “Something went wrong. Please try again later.”
• What happened? → Problem on server side

API Meaning:
Server failed internally → 500 Internal Server Error