API Testing Interview Questions and Answers for Freshers and Experience

In the world of modern software development, APIs (Application Programming Interfaces) play a crucial role in enabling communication between different software systems. With the rise of microservices, cloud-based architecture, and mobile-first development, API testing has become one of the most in-demand skills for QA professionals.

Whether you're a fresher trying to break into the software testing industry or an experienced professional aiming to move into automation or backend testing, this blog offers a complete set of API Testing Interview Questions and Answers to help you ace your upcoming interview.

What Is API Testing?

API Testing is a type of software testing that focuses on verifying whether APIs work as expected. Unlike UI testing, which interacts with the application through graphical elements, API testing uses tools and frameworks to send calls to the API, receive responses, and validate the results—all without a user interface.

This testing is essential to ensure the reliability, performance, and security of back-end systems.

Why API Testing Matters in Interviews

Employers are increasingly looking for QA engineers who are comfortable testing beyond the UI. Understanding RESTful APIs, using tools like Postman, SoapUI, or Rest Assured, and being able to write automated test scripts are often key requirements in technical interviews for QA and SDET roles.

You can expect a range of questions, from basic concepts to advanced scenario-based challenges, in interviews depending on your level of experience.

Structure of This Blog

This guide includes:

  • Basic and advanced API testing questions

  • Real-world examples and answers

  • Tools and automation frameworks

  • REST and SOAP API concepts

  • HTTP methods and status codes

  • API security and performance questions

  • Scenario-based questions and tips for interviews

Sample API Testing Interview Questions and Answers

Here are just a few examples from the full list covered in the blog:

1. What is an API?

An API (Application Programming Interface) allows two systems to communicate with each other. It exposes a set of endpoints for data exchange between software components.

2. What is API Testing and why is it important?

API Testing validates the functionality, reliability, performance, and security of APIs. It's crucial because it allows you to test the business logic of the application without relying on the frontend.

3. What are the common types of API protocols?

  • REST (Representational State Transfer)

  • SOAP (Simple Object Access Protocol)

  • GraphQL

  • gRPC

4. What tools are used for API Testing?

  • Postman (manual API testing)

  • SoapUI (for SOAP and REST APIs)

  • Rest Assured (Java-based automation)

  • JMeter (for performance testing of APIs)

  • Swagger (API documentation and testing)

5. What are the common HTTP methods used in API testing?

  • GET – retrieve data

  • POST – create data

  • PUT – update data

  • DELETE – delete data

  • PATCH – partially update data

  • OPTIONS – check available methods

6. What is a status code? Give examples.

Status codes are 3-digit numbers returned by servers to indicate the result of the API call.
Examples:

  • 200 – OK

  • 201 – Created

  • 400 – Bad Request

  • 401 – Unauthorized

  • 404 – Not Found

  • 500 – Internal Server Error

7. How do you validate a response in API testing?

By checking:

  • Status code (e.g., 200 OK)

  • Response time

  • Response body content (JSON/XML)

  • Headers and cookies

  • Schema validation

8. What is the difference between PUT and PATCH?

  • PUT updates the entire resource.

  • PATCH updates only the specified fields of a resource.

9. What is the difference between SOAP and REST APIs?

  • SOAP is protocol-based, uses XML, and is stricter.

  • REST is architecture-based, supports multiple formats (JSON, XML), and is lightweight and flexible.

10. What is Authentication and Authorization in API Testing?

  • Authentication confirms the user’s identity (e.g., using a token or API key).

  • Authorization checks what resources a user can access after authentication.

Scenario-Based Interview Questions

  • How do you test an API that is not documented?

  • How would you automate API testing in a CI/CD pipeline?

  • How do you handle dynamic parameters in API responses?

  • What do you do if the API is rate-limited?

These types of questions are common for experienced professionals and focus on practical problem-solving skills.

For Freshers

Freshers should focus on understanding:

  • Basics of RESTful APIs

  • Tools like Postman

  • Common HTTP methods and status codes

  • Simple validation techniques

  • JSON vs. XML structure

  • Manual testing of APIs using request and response formats

For Experienced Professionals

If you’re experienced, expect deeper questions like:

  • Automating API testing using Rest Assured, Postman (with Newman), or JUnit/TestNG

  • Integrating API tests into Jenkins pipelines

  • Writing API test scripts using scripting languages like JavaScript, Python, or Java

  • Handling authorization protocols (OAuth, JWT, API keys)

  • Validating JSON schema and response structures

  • Load and performance testing of APIs using tools like JMeter

Final Tips to Crack the API Testing Interview

  • Practice using Postman collections and writing tests with JavaScript or Python.

  • Understand how APIs work in a real software project.

  • Be familiar with status codes, request/response structures, and error handling.

  • Prepare to demonstrate how you handled real bugs or created automation suites.

  • For automation-focused roles, highlight frameworks, code snippets, and CI/CD experience.

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