400 Bad Request in Rest API - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the HTTP status code returned?

A client sends a malformed JSON payload to a REST API endpoint expecting JSON data. The server detects the invalid JSON format. What HTTP status code will the server most likely return?

A 200 OK

B 500 Internal Server Error

C 404 Not Found

D 400 Bad Request

💡 Hint

Think about which status code means the client sent something wrong.

The 400 Bad Request status code means the server cannot process the request due to client error, such as malformed JSON.

🧠 Conceptual

intermediate

Cause of 400 Bad Request in REST APIs

Which of the following is the most common cause for a REST API to respond with a 400 Bad Request status?

A The client sent invalid or malformed data

B The server encountered an unexpected error

C The requested resource does not exist

D The client is not authorized to access the resource

💡 Hint

400 means the client made a mistake in the request format or content.

400 Bad Request indicates the client sent invalid data or the request could not be understood by the server.

❓ Predict Output

advanced

Output of server response with missing required field

A REST API expects a JSON body with a required field 'username'. The client sends a JSON without 'username'. The server validates and returns a response. What is the likely HTTP status code and message?

Rest API

POST /api/users HTTP/1.1
Content-Type: application/json

{"email": "[e-mail]"}

A 500 Internal Server Error

B 400 Bad Request with error message about missing 'username'

C 404 Not Found

D 201 Created with user details

💡 Hint

Missing required fields usually cause client errors.

The server returns 400 Bad Request because the client did not provide a required field, making the request invalid.

🔧 Debug

advanced

Identify the cause of 400 Bad Request in this API call

A client sends this HTTP request to a REST API but receives a 400 Bad Request response. What is the most likely cause?

Rest API

POST /api/login HTTP/1.1
Content-Type: application/json

{"username": "user1", "password": "12345"}

A Password should be a string, not a number

B Missing Authorization header

C Incorrect HTTP method used

D Server is down

💡 Hint

Check the data types expected by the API.

The API expects the password as a string, but the client sent a number, causing a validation error and 400 Bad Request.

🚀 Application

expert

How to handle 400 Bad Request in client code

You are writing client code to call a REST API. If the server responds with 400 Bad Request, what is the best way to handle it?

A Ignore the error and continue

B Retry the request immediately without changes

C Log the error and prompt the user to correct the input data

D Restart the client application

💡 Hint

400 means the client sent bad data, so fix the data before retrying.

When receiving 400 Bad Request, the client should inform the user to fix the input data before retrying.