JSON Quiz Test Online (30 random Questions) 2026

This quick 30-minute challenge consists of 30 random multiple-choice questions designed to test your knowledge across various JSON topics, including the introduction to JSON, JSON syntax and basics, data types, operations in JavaScript, APIs and JSON, advanced structures, JSON Schema, tools and debugging, as well as performance and security considerations. Whether you’re new to JSON or looking to refine your skills, this quiz will enhance your understanding of JSON’s role in modern web development.

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30 Minutes JSON Quiz Test Online

Welcome to the JSON Quiz! This quick 30-minute challenge consists of 30 random multiple-choice questions designed to test your knowledge across various JSON topics, including the introduction to JSON, JSON syntax and basics, data types, operations in JavaScript, APIs and JSON, advanced structures, JSON Schema, tools and debugging, as well as performance and security considerations. Whether you're new to JSON or looking to refine your skills, this quiz will enhance your understanding of JSON's role in modern web development.

1 / 30

1. Which keyword restricts the number of items in a JSON array?

A) maxItems

B) minLength

C) maxSize

D) arrayLimit

2 / 30

2. How can you identify unused keys in a JSON object?

A) Postman

B) JSONLint

C) Static analysis tools or manual comparison

D) JSON Formatter

3 / 30

3. What can be the root structure of a JSON document?

A) A string

B) Only an array

C) Either an object or an array

D) Only an object

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4. What is the advantage of using JSON in IoT (Internet of Things) devices?

A) It is faster than wireless communication

B) It provides a lightweight and flexible data format

C) It reduces power consumption

D) It encrypts all data automatically

5 / 30

5. Which online tool is commonly used to format JSON for readability?

A) JSONLint

B) Visual Studio Code

C) Postman

D) GitHub

6 / 30

6. How can you format JSON output with spaces using JSON.stringify()?

A) Pass a null parameter to JSON.stringify()

B) Use JSON.prettyPrint()

C) Use the JSON.stringify(obj, null, 4) method

D) Add a spaces property to the JSON object

7 / 30

7. What does the enum keyword specify in JSON Schema?

A) The maximum length of a string

B) The format of a date field

C) The default value of a property

D) A list of allowed values for a property

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8. What will JSON.stringify(true) return?

A) "True"

B) true

C) Throws an error

D) "true"

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9. Which of these is NOT allowed in JSON arrays?

A) Mixed data types

B) Objects as elements

C) Functions as elements

D) Nested arrays

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10. How do you handle errors in a fetch() request?

A) Using fetchError() function

B) Using try...catch blocks or then().catch() methods

C) Using the error property of the response

D) Errors cannot be handled in fetch()

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11. In which cloud service is JSON commonly used for defining infrastructure as code?

A) DigitalOcean

B) Firebase

C) Microsoft Azure

D) Amazon Web Services (AWS) CloudFormation

12 / 30

12. How can large nested JSON objects impact performance?

A) They slow down parsing and increase memory usage

B) They reduce API latency

C) They make JSON more secure

D) They improve network speed

13 / 30

13. Which of the following values is not valid in JSON?

A) 123

B) "Hello"

C) undefined

D) null

14 / 30

14. Which of the following is a valid JSON array?

A) {"1", "2", "3"}

B) [1; 2; 3]

C) [1, 2, "three"]

D) (1, 2, 3)

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15. Which of the following is the correct JSON format for a key-value pair?

A) {key: value}

B) {"key": "value"}

C) {"key": value}

D) {key = value}

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16. How are key-value pairs separated in a JSON object?

A) Equal sign (=)

B) Colon (:)

C) Comma (,)

D) Semicolon (;)

17 / 30

17. What is the purpose of the dependencies keyword in JSON Schema?

A) To define key dependencies

B) To define type constraints

C) To validate nested objects

D) To specify default values

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18. What is the difference between allOf and oneOf in JSON Schema?

A) allOf validates all schemas, oneOf validates only one schema

B) oneOf requires at least one match, allOf requires none

C) allOf allows duplicates, oneOf does not

D) allOf is for strings, oneOf is for arrays

19 / 30

19. Which browser's developer tools are commonly used to debug JSON in web applications?

A) Firefox

B) Safari

C) Google Chrome

D) Internet Explorer

20 / 30

20. Which of the following is NOT a JSON data type?

A) Null

B) Date

C) String

D) Boolean

21 / 30

21. Can a JSON object be empty?

A) Only when nested

B) Only in arrays

C) No

D) Yes

22 / 30

22. Which JSON data type is used to group key-value pairs?

A) Array

B) String

C) Number

D) Object

23 / 30

23. Which of the following files often uses JSON for configuration?

A) preferences.ini

B) config.txt

C) settings.json

D) config.xml

24 / 30

24. What data type is represented by {} in JSON?

A) Array

B) String

C) Object

D) Null

25 / 30

25. Which of the following best describes JSON?

A) A programming language

B) A lightweight data format

C) A markup language like XML

D) A database system

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26. What does a JSON array of objects look like?

A) { "array": [ "value1", "value2" ] }

B) [ "object1", "object2" ]

C) { "object1": "value1", "object2": "value2" }

D) [ { "key": "value" }, { "key": "value" } ]

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27. What is a common vulnerability associated with parsing untrusted JSON?

A) JSON Flooding

B) JSON Injection

C) JSON Brute Force

D) JSON Parsing Loops

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28. Which of the following is the correct way to represent an empty JSON object?

A) ""

B) {}

C) []

D) null

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29. What is the MIME type for JSON?

A) text/plain

B) text/json

C) application/json

D) application/javascript

30 / 30

30. What is the default value of additionalProperties in JSON Schema?

A) false

B) undefined

C) true

D) null

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