Validation error details in Rest API - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this JSON validation error response?

Consider a REST API that validates user input and returns this JSON error response when the 'email' field is missing. What is the output shown to the client?

Rest API

{
  "errors": {
    "email": ["This field is required."]
  },
  "message": "Validation failed"
}

A {"message":"Validation failed","fields":{"email":"required"}}

B {"error":"email is missing","status":400}

C {"errors":{"email":["This field is required."]},"message":"Validation failed"}

D {"status":"error","details":"email missing"}

💡 Hint

Look for the exact JSON structure that matches the validation error format.

The API returns a JSON object with an 'errors' key containing field-specific messages and a general 'message' key. Option C matches this structure exactly.

❓ Predict Output

intermediate

What error message does this API return for invalid password length?

An API validates a password field and returns this JSON error response if the password is too short. What is the exact error message for the password field?

Rest API

{
  "errors": {
    "password": ["Password must be at least 8 characters."]
  },
  "message": "Validation failed"
}

A Password must be at least 8 characters.

B Password is too short.

C Password length invalid.

D Password must contain letters and numbers.

💡 Hint

Check the exact string inside the password error array.

The error message is exactly 'Password must be at least 8 characters.' as shown in the JSON under the 'password' key.

❓ Predict Output

advanced

What is the output when multiple fields fail validation?

An API returns this JSON when both 'username' and 'email' fields fail validation. What is the exact JSON output?

Rest API

{
  "errors": {
    "username": ["Username already taken."],
    "email": ["Invalid email format."]
  },
  "message": "Validation failed"
}

A {"error":"Multiple validation errors","fields":{"username":"taken","email":"invalid"}}

B {"errors":{"username":["Username already taken."],"email":["Invalid email format."]},"message":"Validation failed"}

C {"message":"Validation failed","errors":["Username already taken.","Invalid email format."]}

D {"errors":{"username":"Username already taken.","email":"Invalid email format."},"message":"Validation failed"}

💡 Hint

Look for the JSON where errors are arrays per field.

The API returns errors as arrays for each field inside the 'errors' object. Option B matches this structure exactly.

❓ Predict Output

advanced

What error does this invalid JSON validation response cause?

This API response is missing a colon after 'errors'. What error will a JSON parser raise?

Rest API

{
  "errors" {
    "email": ["Required field missing."]
  },
  "message": "Validation failed"
}

A JSONDecodeError: Expecting ':' delimiter

B KeyError: 'errors'

C TypeError: string indices must be integers

D No error, valid JSON

💡 Hint

Check the syntax near the 'errors' key.

The missing colon after 'errors' causes a JSONDecodeError expecting a ':' delimiter.

🧠 Conceptual

expert

Which option correctly describes the structure of detailed validation error responses in REST APIs?

In REST API design, detailed validation error responses typically include which of the following structures?

A A flat list of error strings without field association.

B A single error string summarizing all validation issues.

C An array of objects each containing a 'code' and 'description' but no field names.

D An object with a 'message' string and an 'errors' object mapping field names to arrays of error messages.

💡 Hint

Think about how clients identify which fields failed validation.

The standard pattern is to have a general message and an 'errors' object where each field maps to an array of error messages, allowing clients to show specific feedback.