API Testing Interview Questions and Answers

Last updated on Feb 06, 2023
  • Share
API Testing Interview Questions

Ever heard this line by the developer- we have to test this API? Well, APIs are an interesting part of any web application as they let developers share data across different platforms. Today in this article we will get through various API Testing Interview Questions which are commonly asked both fresher and experienced. In the coming years, API Testing will be the future of Software Testing as it has the capabilities to offer testers a more cost-effective way to provide good test coverage in less time. If you gained knowledge about this testing you can shape your future and also earn well.

The average salary of testers who knows API Testing is 10,75,000 per year, candidates who are just familiar and are in entry-level positions can earn up to 7,00,000 per year and those who are experienced can earn around 2,000,000 per year. According to market research, API Testing will display a compound annual growth of 19.9% in 2021-2028 and is expected to reach 3,265.52 million USD by 2028. The growth of API Technology is increasing daily as it is adopted by small, mid-sized, and large enterprises and thus reducing the rising complexities in IT sectors.

Most Frequently Asked API Testing Interview Questions

Here in this article, we will be listing frequently asked API Testing Interview Questions and Answers with the belief that they will be helpful for you to gain higher marks. Also, to let you know that this article has been written under the guidance of industry professionals and covered all the current competencies.

Q1. What is an API and describe the manner they work?

API stands for Application Programming Interface which acts as an interface between two applications and allows them to communicate with each other. In simple words, APIs ensure how one part of the software program interacts with the other part and allow exchanging of data between systems that are located at different remote places.

Working of APIs

Let’s understand this with the help of a simple flow diagram-

API automation interview questions
It is very clear from the diagram the manner APIs work. Imagine you are a customer at a restaurant. The waiter which acts as an intermediary between customers and the kitchen takes an order from the customer and requests it from the kitchen. Finally, he/she provided what you have ordered.
To understand API in technical terms, replace customer with user/ mobile app, a waiter with API, and kitchen with the application/webserver.
Q2. Through API Testing what exactly do we verify?

In API Testing, responses based on the following parameters will get analyzed.

  • Testers or developers have to analyze the data accuracy which they have received by comparing it with the expected response.
  • Time is taken by the API to respond.
  • Error codes need to be analyzed if APIs are expected to throw an error.
  • HTTP status codes.
  • Non-functional specifications like the security, performance, availability, etc. of an application need to be tested.
  • Authorization checks
Q3. What is Rest API and what is the difference between SOAP and Rest API?

Term REST refers to Representational State Transfer which is a set of functions and thus helps developers in making requests along with receiving responses. In Rest API interaction is made with HTTP protocol and in a very short time, it becomes a productive standard for API creation.

SOAP is a protocol and specially designed with a specification. It is an architectural style that doesn’t follow any strict standards but follows some constraints.
Soap only uses XML for exchanging information and data. In Rest API it’s the choice of implementer which data format he/she wants to use such as JSON, Plain-Text, and HTML.
For Security, SOAP use SSL and WS-security and is preferred for the bank account password, card number, etc. It has SSL and HTTPS for security.
SOAP is not generally preferred but used in cases where more reliability and stateful data transfer requires. It is most preferred by developers as it provides more maintainability and scalability.
Q4. List out some challenges faced in API Testing?

Like another software testing, API testing also faces some challenges described below-

  • To know about the proper input values that need to be entered in API inputs because of the absence of GUI.
  • One must have proper knowledge of output verification and validation.
  • Challenge of proper parameter selection and its combination.
  • Strong coding knowledge is a must for testers too.
Q5. How UI Testing is different from API Testing?

UI means User Interface is a type of testing that generally tests the graphical interface means to test how an application is looking, how it is feasible for end-users, Images, buttons, videos, font displayed on UI screen are working as expected.
While API means the program interface that permits communication between two different programs. Its main focus is on the business layer of an application.

Q6. Why is automated API testing useful these days?

When you see the word automation, it means to ease human work with the help of software and tools. 

  • In the coming years, automation testing will cover 80% of the test coverage of any application in a shorter time means automated testing helps to test large and many test cases very easily and quickly.
  • It allows parallel execution and helps in reducing the number of errors that could be generated by humans.
  • It saves the time required to test the applications manually and thus saves the overall cost of any project.
  • Testers don’t have to worry about the part of the application that requires retesting.
  • Helps in identifying defects or bugs at an early phase of development without having any access to the User interface.
Q7. What are the best practices that make API testing successful?

For smooth working and seamless working experience it is advisable to follow some practices that make API Testing more successful-

  • Don’t Repeat Yourself: Avoid repeating the code, in case some tests need the same components and actions it’s better to create a common library.
  • Clarity: Write test cases clearly so that they can be easily debugged. Clear test cases which are running successfully hardly require any attention or time.
  • Mapping and Execution: Design the test in such a way that it can execute in any working environment
  • Utilization of complete API Testing Tool: An all-inclusive API testing tool by your side is very important as it provides features like creating multi-step testing scenarios, effortless testing, tracking API performance, and automated API documentation, etc.
  • Monitor Security Checks: It is a must to design API security test cases for any security breach or flaws.
  • Tackle Negative Testing: Apart from monitoring positive responses one should also opt for negative test results as this process helps in mapping the performance while dealing with issues.
Q8. Tell some API examples which are very popular and well known.
  • Weather Reports: Weather reports can be found on all platforms like Google Search, Apple’s weather app, or from any Smart device. Now, these platforms are not in the business of weather data, so they take this source of information from a third party and do it with the help of API.
  • Log-in Using Facebook/Twitter/Google: You ever saw this sentence “Login to your account” - Every time any application loads, it checks with the help of API if a user is already logged by any of these media, if not API provides identification information.
  • Pay with PayPal: Ever pay using PayPal in any eCommerce store? Well, that also uses API to work and is very similar to the login process.
  • Twitter Bots: All bots means the account that automatically tweets, follows, sends messages are handled by Twitter API.
  • Travel Booking: Ever thought about how travel booking sites can show thousands of flights and destinations with the cheapest option? This is because of using third-party APIs to collect flight information from providers.
Q9. Why API Testing is considered the most suitable form of Automation Testing?

API Testing is considered the most suitable form of Automation Testing because of the following reasons.

  • API testing provides the most stable interface and hence allows two programs to communicate with each other.
  • It provides faster feedback as API acts as an interface between the user and the application. 
  • It successfully validates all the functional paths of the system which are under test.
  • In API testing testers can run API tests without any access to the user interface of software applications.
  • API Testing is language independent and hence users can select any core language when executing automation tests for the application.
Q10. What type of bugs can be found in API Testing?

We have already discussed API Testing in detail, how it provides accuracy in an application and hence capable of finding many types of bugs that includes-

  • Poor Performance
  • Fail to handle requests in a secured manner
  • Duplicate or missing API functionality due to the repetition of code
  • Fail to handle negative test cases
  • If there is heavy traffic or stress, then it is failed to handle that sudden spike.
  • Issues in Multi-threading
  • Improper error codes and status codes
  • Reliability of the software
  • Throw error at unused flags
  • Incompatible error handling process
  • Improper messaging


This article also contains some API automation interview questions in between, hence we have tried to cover all types of API questions in this informative section. Bookmark this page if you are preparing for an API Interview and let us know how it goes. You can also go through different Mock Tests to strengthen this topic. We would love to hear any feedback on this article.

Reviewed and verified by Best Interview Question
Best Interview Question

With our 10+ experience in PHP, MySQL, React, Python & more our technical consulting firm has received the privilege of working with top projects, 100 and still counting. Our team of 25+ is skilled in...