List of most important API testing interview questions.

1- What are the main challenges you face in the API testing in your project?

API documentation

Access to the database

Call sequencing

2- What is the difference between the PUT and the POST method?

  • Firstly, the POST request means creating a new object in the database.
  • Secondly, a PUT request means updating the existing object in the database with the new value.

3- What are the most commonly used HTTP methods?

GET- Used to retrieve data from the serverPOSTcreate a new object in the server

PUT- Used to update an existing object in the serverDELETEused to delete data from the server

4- List a few authentication techniques used in API testing.

  • Session / Cookies based Authentication
  • Basic Authentication
  • Digest Authentication
  • OAuth

Above all are the few most important authentication techniques.

5- What is the REST API?

6- What exactly you verify in API testing?

HTTP status code

Response time

Error codes if API returns an error




Above all are the most important verification checks.

7- Differentiate API testing and UI testing.

API testing allows communication between two software systems. It determines if the developed APIs meets the expectation regarding functionality, reliability, performance, and security. It works on the backend and also knows and the backend testing. To clarify, describe some scenarios while answering this question in an interview.

8- What protocol RESTFUL Web services use?

9- Can we use POST instead of PUT to create a resource?

10- What do you understand by payload?

11- Explain the main differences between API and Web Service?

  • All web services are APIs but not all APIs are web services.
  • A web service uses only three styles of use: SOAP, REST and XML-RPC for communication whereas API may be exposed to in multiple ways.
  • A web service always needs a network to operate while APIs don’t need a network for operation.
  • Web services might not contain all the specifications and cannot perform all the tasks that APIs would perform.

12- List the advantages of API Testing

  • Compatibility and easy integration with GUI: Simple integration would allow new user accounts to be created within the application before a GUI test started.
  • Language-Independent: In API testing, data is exchanged using XML or JSON. These transfer modes are completely language-independent that allows users to select any coding language while adopting automation testing services for the project.
  • Time Effective: In comparison to functional GUI testing API testing usually is less time-consuming. The web elements in GUI testing must be polled, which makes the testing process slower. Particularly, API test automation requires less code so it can provide better and faster test coverage compared to GUI test automation.
  • Test for Core Functionality: API testing provides the ability to access the application without a user interface. The core and code-level functionalities of the application will be tested and evaluated early before the GUI tests. This helps in detecting the minor issues which can become bigger during the GUI testing.

13- What is API Automation?

There are many tools for API automation like-


Katalon studio




CloudQA TruAPI

14- Is there any upper limit for a payload to pass in the POST method?

15- What is REST parameters?

Request parameters — These are submitted as JSON parameters present in the request.

Header parameters — These are present in the request header.

Query string parameters — These are provided at the endpoint of the query.

Path parameters — These are provided in the endpoint path.

For the complete list of API Testing Interview Question visit:




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