Validation error details in Rest API - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a validation error in a REST API?

A validation error happens when the data sent to the API does not meet the rules or format expected. The API then tells you what is wrong so you can fix it.

beginner

Why is it important to provide detailed validation error messages?

Detailed error messages help users or developers understand exactly what data is wrong and how to correct it, making the API easier and faster to use.

beginner

What common information is included in validation error details?

Usually, validation error details include the field name, the error message explaining the problem, and sometimes the invalid value.

intermediate

How should validation errors be structured in a REST API response?

Validation errors are often returned as a JSON object with a list or dictionary of errors, where each error points to a specific field and describes the issue.

beginner

Give an example of a simple validation error response in JSON.

{ "errors": { "email": "Invalid email format", "password": "Password must be at least 8 characters" } }

What does a validation error in a REST API usually indicate?

A The data sent does not meet the expected format or rules

B The server is down

C The API key is missing

D The request method is not supported

Validation errors happen when the input data is incorrect or incomplete, not because of server or method issues.

Which of the following is NOT typically included in validation error details?

A Field name with the error

B Error message explaining the problem

C User's password in plain text

D Invalid value provided

Sensitive data like passwords should never be included in error messages for security reasons.

How are validation errors usually returned in a REST API response?

A As plain text without structure

B As a JSON object listing errors by field

C As an HTML page

D As a binary file

JSON is the standard format for REST API responses, especially for structured error messages.

Why should validation error messages be clear and specific?

A To help users fix their input quickly

B To confuse the user

C To hide the error details

D To slow down the API response

Clear messages improve user experience by guiding users to correct mistakes easily.

Which HTTP status code is commonly used for validation errors?

A 500 Internal Server Error

B 200 OK

C 404 Not Found

D 400 Bad Request

400 Bad Request indicates the client sent invalid data, which fits validation errors.

Explain what validation error details are and why they matter in REST APIs.

Think about what happens when data sent to an API is wrong.

Describe how you would structure a JSON response to show validation errors for multiple fields.

Imagine telling a friend exactly which parts of a form they filled out wrong.

Practice

1. What is the main purpose of validation error details in a REST API response?

easy

A. To explain which input fields are wrong and why

B. To speed up the server response time

C. To encrypt the data sent to the client

D. To log user activity for analytics

Solution

1. Step 1: Understand validation errors

   Validation errors tell us what input data is incorrect or missing.

2. Step 2: Purpose of error details

   Error details explain which fields caused the problem and why, helping fix input.

3. Final Answer:

   To explain which input fields are wrong and why -> Option A

4. Quick Check:

   Validation error details = Explain input errors [OK]

Hint: Validation errors show what and why input is wrong [OK]

Common Mistakes:

• Thinking error details speed up server
• Confusing error details with encryption
• Assuming error details are for logging only

2. Which of the following is the correct JSON structure for validation error details in a REST API?

easy

A. {"data": {"email": "[e-mail]"}}

B. ["email", "password"]

C. {"status": 200, "message": "Success"}

D. {"errors": {"email": "Invalid format", "password": "Too short"}}

Solution

1. Step 1: Identify error details format

   Error details usually use a JSON object with field names as keys and error messages as values.

2. Step 2: Check options

   {"errors": {"email": "Invalid format", "password": "Too short"}} shows a JSON object with "errors" key and field-specific messages, which is correct.

3. Final Answer:

   {"errors": {"email": "Invalid format", "password": "Too short"}} -> Option D

4. Quick Check:

   Validation errors = JSON object with field messages [OK]

Hint: Look for JSON object with field names and error messages [OK]

Common Mistakes:

• Using arrays instead of objects for errors
• Confusing success response with error details
• Missing field names in error messages

3. Given this JSON error response:

{"errors": {"username": "Required field", "age": "Must be a number"}}

What message should the client show for the 'age' field?

medium

A. Must be a number

B. Invalid email format

C. Required field

D. Password too short

Solution

1. Step 1: Read the JSON error response

   The error for "age" is "Must be a number".

2. Step 2: Match the message to the field

   The client should show the message exactly as given for the "age" field.

3. Final Answer:

   Must be a number -> Option A

4. Quick Check:

   Field 'age' error = Must be a number [OK]

Hint: Match field name to its error message in JSON [OK]

Common Mistakes:

• Mixing error messages between fields
• Showing unrelated error messages
• Ignoring the JSON structure

4. You receive this validation error JSON:

{"error": "Invalid input", "fields": ["email", "password"]}

What is wrong with this error detail format?

medium

A. It correctly shows error details

B. It uses a list instead of mapping fields to messages

C. It uses wrong HTTP status code

D. It encrypts error messages

Solution

1. Step 1: Analyze error detail format

   The "fields" key has a list of field names but no messages explaining the errors.

2. Step 2: Identify correct format

   Validation error details should map each field to a specific error message, not just list fields.

3. Final Answer:

   It uses a list instead of mapping fields to messages -> Option B

4. Quick Check:

   Error details need field-message pairs [OK]

Hint: Error details need field names paired with messages [OK]

Common Mistakes:

• Listing fields without error explanations
• Assuming any error JSON is correct
• Ignoring the need for descriptive messages

5. You want to design a REST API validation error response that shows multiple errors per field. Which JSON structure correctly supports this?

hard

A. {"errors": ["email: Required", "password: Too short"]}

B. {"error": "Multiple errors found"}

C. {"errors": {"email": ["Required", "Invalid format"], "password": ["Too short"]}}

D. {"fields": ["email", "password"]}

Solution

1. Step 1: Understand multiple errors per field

   To show many errors for one field, use a list (array) of messages for that field.

2. Step 2: Check JSON structures

   {"errors": {"email": ["Required", "Invalid format"], "password": ["Too short"]}} uses a dictionary with field keys and lists of error messages, which fits the need.

3. Final Answer:

   {"errors": {"email": ["Required", "Invalid format"], "password": ["Too short"]}} -> Option C

4. Quick Check:

   Multiple errors per field = list of messages [OK]

Hint: Use lists inside error fields to show multiple messages [OK]

Common Mistakes:

• Using flat lists without field keys
• Not supporting multiple messages per field
• Using vague error messages without details