JSON body in Postman - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a JSON body in API testing?

A JSON body is the data sent in the request payload formatted as JSON. It tells the server what information the client wants to send or update.

beginner

Why do we use JSON format for request bodies in Postman?

JSON is easy to read and write, lightweight, and widely supported by APIs. It helps structure data clearly for communication between client and server.

beginner

How do you set a JSON body in Postman?

In Postman, select the 'Body' tab, choose 'raw', then select 'JSON' from the dropdown. Then type or paste your JSON data.

intermediate

What happens if your JSON body is not valid?

The server may reject the request with an error, or the API may not work as expected. Postman also shows an error if JSON syntax is incorrect.

beginner

Give an example of a simple JSON body for creating a user with name and email.

{ "name": "Alice", "email": "[e-mail]" }

What format should the request body be in when sending JSON data in Postman?

A raw with JSON selected

B form-data

C x-www-form-urlencoded

D binary

To send JSON data, you must select 'raw' and then choose 'JSON' so Postman sends the data correctly.

Which of these is a valid JSON body?

A <name>Bob</name>

B {name: 'Bob', age: 30}

C {"name": "Bob", "age": 30}

D name=Bob&age=30

Valid JSON requires double quotes around keys and string values, like in option A.

What error might you get if your JSON body is missing a closing brace?

A 401 Unauthorized

B SyntaxError or parsing error

C 404 Not Found

D Timeout error

Missing braces cause syntax errors because the JSON is not well-formed.

In Postman, where do you enter the JSON body for a POST request?

A Body tab

B Headers tab

C Params tab

D Authorization tab

The Body tab is where you input the data you want to send in the request.

Why is JSON preferred over XML for API request bodies?

A JSON is heavier and slower

B JSON requires special software to read

C XML is not supported by APIs

D JSON is easier to read and write

JSON is lightweight and easier for humans and machines to read and write compared to XML.

Explain how to create and send a JSON body in Postman for an API request.

Think about the steps in Postman interface to send JSON data.

Describe common errors that can happen with JSON bodies and how to avoid them.

Consider what makes JSON invalid and how Postman helps.

Practice

1. What is the correct way to represent a JSON body with a user's name and age in Postman?

easy

A. {"name": "Alice", "age": 30}

B. {name: Alice, age: 30}

C. {'name': 'Alice', 'age': 30}

D. {name = "Alice", age = 30}

Solution

1. Step 1: Identify JSON syntax rules

   JSON keys and string values must be in double quotes. Numbers do not need quotes.

2. Step 2: Check each option for correct JSON format

   {"name": "Alice", "age": 30} uses double quotes correctly around keys and string values. The other options use incorrect quotes or syntax.

3. Final Answer:

   {"name": "Alice", "age": 30} -> Option A

4. Quick Check:

   JSON keys and strings use double quotes = A [OK]

Hint: Always use double quotes for keys and string values in JSON [OK]

Common Mistakes:

• Using single quotes instead of double quotes
• Omitting quotes around keys
• Using equal signs instead of colons

2. Which of the following is a valid JSON body to send a list of colors in Postman?

easy

A. {"colors": ("red", "green", "blue")}

B. {colors: [red, green, blue]}

C. {"colors": "red", "green", "blue"}

D. {"colors": ["red", "green", "blue"]}

Solution

1. Step 1: Understand JSON array syntax

   Arrays in JSON are enclosed in square brackets with comma-separated values, strings in double quotes.

2. Step 2: Validate each option's array format

   {"colors": ["red", "green", "blue"]} correctly uses square brackets and double quotes. The other options are invalid: one uses parentheses, another is missing array brackets, and one lacks quotes around strings and keys.

3. Final Answer:

   {"colors": ["red", "green", "blue"]} -> Option D

4. Quick Check:

   Arrays use square brackets and double quotes = B [OK]

Hint: Use square brackets for arrays and double quotes for strings [OK]

Common Mistakes:

• Using parentheses instead of square brackets
• Missing quotes around string values
• Omitting brackets for arrays

3. Given this JSON body sent in Postman:

{
  "user": {
    "id": 101,
    "active": true
  },
  "roles": ["admin", "editor"]
}

What is the value of user.active?

medium

A. null

B. true

C. false

D. "true"

Solution

1. Step 1: Locate the key user.active in the JSON

   Inside the "user" object, the key "active" has the value true without quotes, meaning boolean true.

2. Step 2: Understand JSON boolean values

   Boolean true is a literal, not a string. So the value is the boolean true, not the string "true".

3. Final Answer:

   true -> Option B

4. Quick Check:

   Boolean true is unquoted true = D [OK]

Hint: Booleans in JSON are unquoted true or false [OK]

Common Mistakes:

• Confusing boolean true with string "true"
• Assuming missing keys have null values
• Misreading nested object structure

4. You wrote this JSON body in Postman:

{
  "product": "Book",
  "price": 12.99,
  "inStock": yes
}

What is the error in this JSON body?

medium

A. "price" should be a string in quotes

B. "inStock" value should be true or false without quotes

C. "inStock" value 'yes' is invalid, should be true or false

D. Missing comma after "price" value

Solution

1. Step 1: Check the value of "inStock" key

   The value 'yes' is not a valid JSON boolean or string because it lacks quotes.

2. Step 2: Identify correct boolean values in JSON

   JSON booleans are true or false without quotes. Strings must be in double quotes. 'yes' without quotes is invalid.

3. Final Answer:

   "inStock" value 'yes' is invalid, should be true or false -> Option C

4. Quick Check:

   Boolean values must be true/false unquoted = C [OK]

Hint: Use true/false for booleans, not yes/no or strings [OK]

Common Mistakes:

• Using yes/no instead of true/false
• Not quoting string values
• Confusing number and string types

5. You want to send this JSON body in Postman to update a user's profile:

{
  "user": {
    "name": "Bob",
    "email": "[e-mail]",
    "preferences": {
      "notifications": false,
      "themes": ["dark", "blue"]
    }
  }
}

Which of the following changes will correctly add a new preference "language" set to "en" inside "preferences"?

hard

A. { "user": { "name": "Bob", "email": "[e-mail]", "preferences": { "notifications": false, "themes": ["dark", "blue"], "language": "en" } } }

B. { "user": { "name": "Bob", "email": "[e-mail]", "preferences": { "notifications": false, "themes": ["dark", "blue"] }, "language": "en" } }

C. { "user": { "name": "Bob", "email": "[e-mail]", "preferences": { "notifications": false, "themes": ["dark", "blue"] }, "preferences.language": "en" } }

D. { "user": { "name": "Bob", "email": "[e-mail]", "preferences": { "notifications": false, "themes": ["dark", "blue"] }, "preferences": { "language": "en" } } }

Solution

1. Step 1: Understand nested object update in JSON

   To add a new key inside "preferences", it must be inside the existing "preferences" object.

2. Step 2: Check each option's structure

   { "user": { "name": "Bob", "email": "[e-mail]", "preferences": { "notifications": false, "themes": ["dark", "blue"], "language": "en" } } } adds "language": "en" inside "preferences" correctly. { "user": { "name": "Bob", "email": "[e-mail]", "preferences": { "notifications": false, "themes": ["dark", "blue"] }, "language": "en" } } adds "language" outside "preferences". { "user": { "name": "Bob", "email": "[e-mail]", "preferences": { "notifications": false, "themes": ["dark", "blue"] }, "preferences.language": "en" } } uses invalid key "preferences.language". { "user": { "name": "Bob", "email": "[e-mail]", "preferences": { "notifications": false, "themes": ["dark", "blue"] }, "preferences": { "language": "en" } } } overwrites "preferences" object, losing existing keys.

3. Final Answer:

   { "user": { "name": "Bob", "email": "[e-mail]", "preferences": { "notifications": false, "themes": ["dark", "blue"], "language": "en" } } } -> Option A

4. Quick Check:

   Nested keys must be inside existing objects = A [OK]

Hint: Add new keys inside existing nested objects, not outside [OK]

Common Mistakes:

• Adding keys outside nested objects
• Using dot notation as key name
• Overwriting entire nested objects accidentally