REST API fundamentals review in Postman

Introduction

REST APIs let different software talk to each other over the internet. Testing them ensures they work correctly and return the right data.

When you want to check if a website or app can get data from a server.

When you need to verify that sending data to a server saves it properly.

When you want to make sure deleting or updating data works as expected.

When you want to test how the server responds to wrong or missing information.

When you want to automate checking your API regularly to catch problems early.

Syntax

Postman

METHOD URL
Headers: key: value
Body: (optional, for POST/PUT/PATCH)

METHOD is the HTTP method like GET, POST, PUT, DELETE, PATCH.

URL is the web address of the API endpoint.

Examples

Fetch a list of users with authorization.

Postman

GET https://api.example.com/users
Headers:
  Authorization: Bearer your_token_here

Create a new user by sending JSON data.

Postman

POST https://api.example.com/users
Headers:
  Content-Type: application/json
Body:
  {"name": "Alice", "email": "[e-mail]"}

Update the email of user with ID 123.

Postman

PUT https://api.example.com/users/123
Headers:
  Content-Type: application/json
Body:
  {"email": "[e-mail]"}

Delete the user with ID 123 using authorization.

Postman

DELETE https://api.example.com/users/123
Headers:
  Authorization: Bearer your_token_here

Sample Program

This request fetches the post with ID 1 from a public test API. It expects JSON data back.

Postman

GET https://jsonplaceholder.typicode.com/posts/1
Headers:
  Accept: application/json

Important Notes

Always set the correct Content-Type header when sending data.

Use authorization headers if the API requires login or tokens.

Check the response status code to know if the request succeeded (e.g., 200 OK, 201 Created).

Summary

REST APIs use HTTP methods to perform actions on data.

Testing REST APIs means sending requests and checking responses.

Postman is a tool that helps you send these requests easily.

Practice

1. Which HTTP method is typically used to retrieve data from a REST API without changing it?

easy

A. POST

B. GET

C. PUT

D. DELETE

Solution

1. Step 1: Understand HTTP methods

   GET is used to request data without modifying it, while POST, PUT, DELETE change data.

2. Step 2: Identify method for data retrieval

   Since we want to retrieve data without changes, GET is the correct method.

3. Final Answer:

   GET -> Option B

4. Quick Check:

   Retrieve data = GET [OK]

Hint: GET is for reading data, others modify it [OK]

Common Mistakes:

• Confusing POST with GET for data retrieval
• Using DELETE to get data
• Thinking PUT retrieves data

2. Which of the following is the correct way to set the HTTP method to POST in Postman?

easy

A. Add 'method: POST' in the Headers tab

B. Type 'POST' in the URL field

C. Select POST from the dropdown next to the URL input

D. Use the Body tab to set method to POST

Solution

1. Step 1: Locate HTTP method selector in Postman

   Postman has a dropdown menu next to the URL field to choose HTTP methods.

2. Step 2: Confirm correct method selection

   Selecting POST from this dropdown sets the request method properly.

3. Final Answer:

   Select POST from the dropdown next to the URL input -> Option C

4. Quick Check:

   Method dropdown sets HTTP method [OK]

Hint: Use dropdown near URL to pick method [OK]

Common Mistakes:

• Typing method name in URL field
• Trying to set method in Headers
• Confusing Body tab with method setting

3. What will be the status code returned by a successful DELETE request in a REST API?

medium

A. 404 Not Found

B. 201 Created

C. 200 OK

D. 204 No Content

Solution

1. Step 1: Understand DELETE success responses

   A successful DELETE often returns 204 No Content, meaning the resource was deleted and no content is returned.

2. Step 2: Compare other status codes

   200 OK means success with content, 201 Created is for new resource creation, 404 Not Found means resource missing.

3. Final Answer:

   204 No Content -> Option D

4. Quick Check:

   DELETE success = 204 No Content [OK]

Hint: DELETE success usually returns 204 No Content [OK]

Common Mistakes:

• Choosing 201 Created for DELETE
• Assuming 200 OK always returns content
• Confusing 404 with success

4. You send a POST request in Postman but get a 405 Method Not Allowed error. What is the most likely cause?

medium

A. The API endpoint does not support POST method

B. The URL is incorrect

C. The request body is empty

D. The server is down

Solution

1. Step 1: Understand 405 error meaning

   405 Method Not Allowed means the server recognizes the URL but the HTTP method used is not supported on that endpoint.

2. Step 2: Eliminate other options

   Incorrect URL usually gives 404, empty body usually does not cause 405, server down causes no response or 5xx errors.

3. Final Answer:

   The API endpoint does not support POST method -> Option A

4. Quick Check:

   405 = Method not allowed on endpoint [OK]

Hint: 405 means method not allowed on URL [OK]

Common Mistakes:

• Confusing 405 with 404 Not Found
• Assuming empty body causes 405
• Thinking server down causes 405

5. You want to test a REST API endpoint that updates user data. Which combination of HTTP method and Postman feature is best to use?

hard

A. PUT method with Body tab to send JSON data

B. GET method with Params tab to send JSON data

C. DELETE method with Headers tab to send JSON data

D. POST method with URL query parameters

Solution

1. Step 1: Identify method for updating data

   PUT is the standard HTTP method to update existing data in REST APIs.

2. Step 2: Choose Postman feature to send data

   The Body tab allows sending JSON data payload, which is needed to update user data.

3. Step 3: Evaluate other options

   GET does not update data, DELETE removes data, and URL query parameters are not suitable for sending JSON update data.

4. Final Answer:

   PUT method with Body tab to send JSON data -> Option A

5. Quick Check:

   Update data = PUT + Body JSON [OK]

Hint: Use PUT with Body for updates in Postman [OK]

Common Mistakes:

• Using GET to update data
• Sending JSON in URL parameters
• Confusing DELETE with update