Top 50 API Testing Interview Questions and Answers 2026 Guide with REST Assured examples
BlogsAPI Testing

Top 50 API Testing Interview Questions with Answers (2026 Guide)

By Ajit Marathe
7 Min Read
0

Let’s clear API Testing Interview

Introduction:

API Testing is one of the most critical skills for QA engineers in today’s software industry. Modern applications rely heavily on microservices, where APIs act as the backbone of communication between systems. As a result, interviewers expect candidates to have a strong understanding of API concepts, HTTP protocols, authentication mechanisms, and automation tools like REST Assured.

Preparing for an API Testing Interview requires both theoretical knowledge and hands-on experience. In a real API Testing Interview, interviewers expect you to explain concepts, write REST Assured code, and handle real-world scenarios.

In this comprehensive guide on API Testing Interview Questions, we cover the most commonly asked questions along with detailed explanations, practical examples, and real-world testing scenarios. This guide is designed not just to help you answer interview questions but to think like a tester, debug like an engineer, and perform like a professional.

📚 Table of Contents

  1. Basic API Testing Concepts
  2. HTTP Methods & Status Codes
  3. REST Assured Interview Questions (with Code)
  4. API Authentication & Security
  5. Advanced API Testing Concepts
  6. Real-World Scenarios
  7. Best Practices & Interview Tips

With hands-on experience in API automation and real-world QA projects, this guide is designed from a practical interview perspective. As a QA professional working extensively with REST APIs, automation frameworks, and tools like REST Assured, the focus here is not just on theory but on solving real interview scenarios.

In most API Testing Interview rounds, candidates struggle not because of lack of knowledge, but due to lack of clarity in explaining concepts and applying them practically. This guide bridges that gap by combining concepts, code, and real-world examples to help you confidently crack your next interview.

Related API Testing Guides

To master this API Testing Interview, explore these detailed guides:

SECTION 1: BASIC API TESTING INTERVIEW QUESTIONS

1. What is API?

An API (Application Programming Interface) is a set of rules and protocols that allows two software systems to communicate with each other. It acts as an intermediary between a client (frontend) and a server (backend).

Example:

When you open an app and fetch user details:

  • The frontend sends a request to an API
  • The API processes the request
  • The backend sends a response back to the frontend

👉 APIs eliminate the need for direct database interaction and ensure secure, structured communication.

2. What is API Testing?

API Testing is a type of software testing where APIs are tested directly to verify:

  • Functionality (Does it work?)
  • Reliability (Is it stable?)
  • Performance (Is it fast?)
  • Security (Is it safe?)

Unlike UI testing, API testing focuses on the business logic layer, making it faster and more reliable.

3. What are the types of APIs?

One of the most asked API Interview Questions. There are mainly three types of APIs:

1. REST API

Uses HTTP methods and JSON format. Most commonly used.

2. SOAP API

Uses XML format and strict protocols.

3. GraphQL API

Allows clients to request only required data.

👉 In interviews, REST APIs are most commonly asked.

4. What is REST API?

REST (Representational State Transfer) is an architectural style where APIs use HTTP methods to perform operations on resources.

Example:

  • GET → Fetch data
  • POST → Create data
  • PUT → Update data
  • DELETE → Delete data

👉 REST APIs are stateless, meaning each request is independent.

5. What is an Endpoint?

An endpoint is a specific URL where an API can be accessed.

Example:

https://api.example.com/users

👉 This endpoint is used to fetch or manipulate user data.

6. What is Request and Response?

Request:

Sent by the client to the server. It includes:

  • URL
  • Headers
  • Body

Response:

Returned by the server. It includes:

  • Status Code
  • Headers
  • Body

👉 A tester validates both request and response.

7. What is JSON?

JSON (JavaScript Object Notation) is a lightweight data format used in APIs.

{
  "name": "Ajit",
  "role": "QA"
}

👉 JSON is easy to read and widely used in REST APIs.

8. What is API Contract?

An API contract defines how a client and server communicate. It includes:

  • Request format
  • Response format
  • Status codes

👉 Tools like Swagger define API contracts.

9. What tools are used for API Testing?

Common tools include:

  • Postman (Manual testing)
  • REST Assured (Automation)
  • SoapUI (SOAP APIs)

👉 For deep automation, refer:
https://qatribe.in/rest-assured-interview-questions/

10. Difference between API Testing and UI Testing?

API TestingUI Testing
FastSlow
Backend logicFrontend
StableFlaky

👉 API testing is preferred in automation.

SECTION 2: HTTP METHODS & STATUS CODES in API Testing Interview Scenarios

11. What are HTTP Methods?

HTTP methods define actions performed on resources:

  • GET → Retrieve data
  • POST → Create data
  • PUT → Update data
  • DELETE → Remove data

👉 Each method has a specific purpose and behavior.

12. What is Idempotency?

An API is idempotent if multiple identical requests produce the same result.

Example:

PUT request updating user name → same result every time.

👉 GET and PUT are idempotent.

13. What is HTTP Status Code?

A status code indicates the result of an API request.

One of the most common interview questions which will dig-in which status code you have tested.

CodeMeaning
200Success
201Created
400Bad Request
401Unauthorized
403Forbidden
404Not Found
500Server Error

15. How to validate status code using REST Assured?

given()
.when()
.get("/users")
.then()
.statusCode(200);

👉 This ensures API returned expected response.

16. What is 201 Created?

Indicates resource was successfully created.

17. Difference between 401 and 403?

  • 401 → Authentication failed
  • 403 → Access denied

18. What is 404 Not Found?

API endpoint or resource not found.

19. What is 500 Internal Server Error?

Indicates server-side issue.

20. How do you handle negative scenarios?

Test invalid inputs and validate error responses.

SECTION 3: REST ASSURED API Testing Interview With Real-World Scenarios

👉 Advanced:
https://qatribe.in/advanced-rest-assured-interview-questions/

21. What is REST Assured?

REST Assured is a Java library used for automating REST APIs.

22. Basic GET Request

given()
.baseUri("https://reqres.in/api")
.when()
.get("/users/2")
.then()
.statusCode(200);

23. Validate response body

.then()
.body("data.id", equalTo(2));

Below we will talk about POST, PUT,Delete request which is fundamental API testing interview question.

24. POST Request Example

given()
.header("Content-Type", "application/json")
.body("{\"name\":\"Ajit\"}")
.when()
.post("/users")
.then()
.statusCode(201);

👉 Status 201 ensures resource creation.

25. PUT Request

given()
.body("{\"name\":\"Updated\"}")
.when()
.put("/users/2")
.then()
.statusCode(200);

26. DELETE Request

when()
.delete("/users/2")
.then()
.statusCode(204);

27. What is BDD in REST Assured?

  • Given → Setup
  • When → Action
  • Then → Validation

28. How to log response?

.then().log().all();

29. What is JSON Path?

Used to extract values from response.

30. Extract value example

String id = response.jsonPath().getString("id");

SECTION 4: API AUTHENTICATION

👉 Full guide:
https://qatribe.in/the-ultimate-api-authentication-guide-for-beginners-basic-apikey-jwt-oauth/

31. What is Authentication?

No API testing interview will be completed without this question.Authentication verifies user identity before allowing access to API resources. It ensures that only valid users or systems can interact with APIs.

In real-world applications like banking or e-commerce, authentication prevents unauthorized access to sensitive data such as account details or payment information.

32. What are the types of API Authentication?

Common types include:

  • Basic Authentication: Uses username and password encoded in base64.
  • API Key Authentication: Uses a unique key passed in headers or query parameters.
  • Bearer Token Authentication: Uses tokens (like JWT) passed in headers.
  • OAuth 2.0: Secure authorization framework used in enterprise systems.
  • JWT (JSON Web Token): Compact token containing user data and signature.

👉 Each method is used based on security requirements.

33. Bearer Token Example in REST Assured

given()
.header("Authorization", "Bearer token_value")
.when()
.get("/user/profile")
.then()
.statusCode(200);

👉 Here:

  • Authorization header carries token
  • API validates token before responding

34. What is JWT?

JWT (JSON Web Token) is a secure way to transmit data between client and server.

Structure:

  • Header
  • Payload
  • Signature

👉 Widely used in modern authentication systems.

35. What is OAuth 2.0?

OAuth 2.0 is an authorization framework that allows third-party apps to access resources without sharing credentials.

👉 Example:
Login with Google.

SECTION 5: ADVANCED API TESTING

👉 Deep dive:
https://qatribe.in/advanced-api-testing-interview-questions-answers/

36. What is Schema Validation?

Schema validation ensures API response structure matches expected format.

Example:

.then()
.body(matchesJsonSchemaInClasspath("schema.json"));

👉 This validates:

  • Fields
  • Data types
  • Structure

37. What is Chaining in API Testing?

Chaining means using response data from one API request in another request.

Example:

  • Login API returns token
  • Use token in next API

👉 Very common in real-world testing.

38. What is Mocking?

Mocking simulates API responses without actual backend.

👉 Used when:

  • Backend not ready
  • Testing edge cases

39. What is Rate Limiting?

Limits number of API requests per user.

👉 Example:
100 requests per minute.

40. What is Contract Testing?

Ensures API request/response follows defined contract.

👉 Prevents integration issues.

SECTION 6: REAL-WORLD SCENARIOS

41. How to test Login API?

Validate:

  • Status code (200/401)
  • Token generation
  • Response body

👉 Also test:

  • Invalid credentials
  • Missing fields

42. How to handle dynamic data?

Use variables or extract values from responses.

43. How to test error responses?

Validate:

  • Error message
  • Status code
  • Response format

44. How to validate large JSON?

Use:

  • JSON Path
  • Schema validation

45. How to perform API performance testing?

Use tools like JMeter to simulate load.

46. How to test API security?

Check:

  • Authentication
  • Authorization
  • Data leaks

47. How to test pagination?

Validate:

  • Page size
  • Total records
  • Navigation

48. How to handle API versioning?

Test endpoints like:

  • /v1/users
  • /v2/users

49. How to debug API failures?

Check:

  • Logs
  • Request/response
  • Headers

50. What are API testing best practices?

  • Validate all responses
  • Automate critical APIs
  • Test edge cases
  • Use proper assertions

🎯 Conclusion

Mastering these API Testing Interview Questions will help you build a strong foundation in API testing, automation, and real-world problem solving. Focus on understanding concepts, practicing with tools like REST Assured, and handling real scenarios.

Mastering API Testing Interview questions requires strong fundamentals, practical knowledge, and real-world experience. If you prepare these API Testing Interview topics properly, you can confidently crack any QA interview.

💣 Final Interview Advice

Don’t just memorize answers.

👉 Explain clearly
👉 Write code confidently
👉 Think like a tester

👉 That’s how you get selected.

🔗 External Resources & References

For deeper understanding of API testing concepts, HTTP standards, and automation tools, refer to these trusted resources:

❓ FAQ – API Testing Interview

Q1. What is API Testing Interview?
API Testing Interview focuses on backend testing concepts, HTTP methods, REST Assured, and real-world scenarios.

Q2. Is REST Assured mandatory for API interviews?
Yes, most companies expect hands-on knowledge of REST Assured for automation.

Q3. What are important topics in API Testing Interview?
HTTP methods, status codes, authentication, JSON handling, and automation.

Tags:

Author

Ajit Marathe

Follow Me
Other Articles
No Comment! Be the first one.

Leave a Reply

Your email address will not be published. Required fields are marked *