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

A) Postman

B) JSON Formatter

C) Static analysis tools or manual comparison

D) JSONLint

2 / 30

2. How are negative numbers represented in JSON?

A) -123

B) negative123

C) (123)

D) [123]

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3. What is the root element of a JSON document?

A) A string

B) A number

C) A key-value pair

D) An object or array

4 / 30

4. Which attack can occur when JSON data is excessively large and causes resource exhaustion?

A) Remote Code Execution

B) Cross-Site Scripting (XSS)

C) SQL Injection

D) Denial of Service (DoS)

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5. How can JSON responses be protected from being cached by unauthorized users?

A) Convert JSON to XML

B) Use large nested objects

C) Use the Cache-Control header with no-store

D) Minify the JSON data

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6. How are floating-point numbers represented in JSON?

A) "1.23"

B) float(1.23)

C) 1.23

D) 1.23f

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7. Which of the following methods parses a JSON response in JavaScript?

A) JSON.fetch()

B) JSON.stringify()

C) JSON.parse()

D) JSON.decode()

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

A) Date

B) Number

C) String

D) Array

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9. What is the purpose of the Authorization header in API requests?

A) To include authentication credentials

B) To specify data format

C) To set request priority

D) To specify the API version

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10. What type of data does a JSON object contain?

A) Only text

B) Only arrays

C) Key-value pairs

D) Only numbers

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11. What happens if a key in a JSON object contains special characters?

A) It throws an error

B) The key is ignored

C) The special characters are escaped automatically

D) The key must be enclosed in double quotes

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12. Which HTTP header is critical for securing JSON responses?

A) X-Content-Type-Options

B) Content-Type

C) Accept-Encoding

D) Access-Control-Allow-Origin

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13. Can JSON values be arrays?

A) Yes

B) No

C) Only for strings

D) Only in objects

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14. What happens when you use JSON.stringify() on an object with a circular reference?

A) It throws a TypeError

B) It converts the object to a string successfully

C) It throws a syntax error

D) It ignores the circular reference

15 / 30

15. Which of the following tools allows real-time collaboration on JSON data?

A) Google Docs

B) JSONLint

C) JSON Editor Online

D) JIRA

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16. What is the output of the code: JSON.stringify({ key: undefined, key2: "value" });

A) {"key": "", "key2": "value"}

B) {"key2": "value"}

C) {"key": null, "key2": "value"}

D) {"key": undefined, "key2": "value"}

17 / 30

17. Which keyword defines a numeric range in JSON Schema?

A) range

B) numberRange

C) minimum and maximum

D) min and max

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18. How do you access the name of the first employee in the JSON structure { "department": { "employees": [ { "name": "John" }, { "name": "Alice" } ] } }?

A) employees[0].name

B) department[employees][name]

C) department.employees[1].name

D) department.employees[0].name

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19. What is the primary advantage of using binary JSON formats like BSON?

A) Automatic validation

B) Compatibility with XML

C) Enhanced readability

D) Smaller size and faster parsing

20 / 30

20. Which data structure is not directly supported by JSON?

A) String

B) Set

C) Array

D) Object

21 / 30

21. How does HTTPS improve the security of JSON data transmission?

A) It beautifies JSON responses

B) It validates JSON schemas

C) It makes JSON larger

D) It encrypts JSON data in transit

22 / 30

22. Which of the following is a common use of JSON in web development?

A) Defining CSS styles

B) Compiling JavaScript code

C) Storing and exchanging data between client and server

D) Rendering HTML elements

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23. How can you debug a failing JSON API request in a browser?

A) Validate the response JSON using a linter

B) All of the above

C) Use console.log for JSON output

D) Check the network tab in developer tools

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24. Which of the following is an example of a valid JSON number?

A) "123"

B) 123.45

C) 123

D) Both B and C

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25. Which messaging protocol often uses JSON for message payloads?

A) MQTT

B) FTP

C) SMTP

D) POP3

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26. Can a JSON object have duplicate keys?

A) Only in arrays

B) No

C) Yes

D) Only in nested objects

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27. Which of these web technologies heavily relies on JSON for communication?

A) SOAP

B) WebSockets

C) HTTP/2

D) GraphQL

28 / 30

28. How does Firebase use JSON?

A) For real-time database storage and synchronization

B) To render user interfaces

C) To manage authentication tokens

D) To define cloud functions

29 / 30

29. Which of the following is a commonly used library for making API requests in JavaScript?

A) Axios

B) jQuery

C) Lodash

D) D3.js

30 / 30

30. What does the Content-Security-Policy header do for JSON responses?

A) Defines the format of JSON data

B) Ensures JSON is minified

C) Restricts where JSON can be loaded from to prevent cross-site scripting (XSS) attacks

D) Specifies how JSON is cached

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