API Manual Testing Interview Questions

Introduction – Why API Testing Is Important in Interviews

In today’s software landscape, applications rely heavily on APIs to connect web apps, mobile apps, databases, and third-party services. Because of this, interviewers frequently ask api manual testing interview questions to evaluate whether a candidate understands backend validation, request–response flow, and real-time defect detection—without depending on automation.

For freshers, interviewers focus on fundamentals like HTTP methods, status codes, and Postman usage.
For experienced testers, they look for real-time scenarios, negative testing, API chaining, and business-rule validation.

This article is a complete interview guide covering theory, practical examples, sample responses, and scenario-based questions—perfect for manual API testing roles.

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What Is API Testing? (Clear & Simple)

API testing is the process of validating application programming interfaces by sending requests and checking responses for correctness, reliability, performance, and security—without using the UI.

In simple terms:

API testing ensures the backend logic works exactly as expected.

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REST vs SOAP vs GraphQL

Feature	REST	SOAP	GraphQL
Type	Architectural style	Protocol	Query language
Data format	JSON	XML	JSON
Performance	Fast & lightweight	Slower	Optimized
Flexibility	High	Low	Very high
Usage	Most modern apps	Legacy systems	Modern frontend apps

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70+ API Manual Testing Interview Questions & Answers

Basic API Manual Testing Questions (Freshers)

1. What is API manual testing?
   API manual testing involves testing APIs by manually sending requests and validating responses using tools like Postman.
   
2. Why is API testing important?
   It validates core business logic and data flow early in development.
   
3. What is an API?
   API allows two applications to communicate with each other.
   
4. What tools are used for manual API testing?
   Postman, SoapUI, browser developer tools, curl.
   
5. What is an endpoint?
   A URL where an API receives requests.
   
6. What is a request payload?
   Data sent to the server in POST/PUT/PATCH requests.
   
7. What is a response payload?
   Data returned by the server after processing the request.
   
8. What are HTTP headers?
   Metadata like Content-Type, Authorization, Accept.
   
9. What is Content-Type?
   Specifies the format of request/response (application/json).
   
10. What is statelessness in REST?
    Each request is independent and contains all required information.
    

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REST API Interview Questions

11. Which HTTP methods are commonly used?
    GET, POST, PUT, PATCH, DELETE.
    
12. Difference between GET and POST?
    GET retrieves data; POST creates data.
    
13. Difference between PUT and PATCH?
    PUT replaces a resource; PATCH updates part of it.
    
14. What is JSON?
    A lightweight data-interchange format.
    

{

  “id”: 101,

  “name”: “Srushti”,

  “role”: “QA Engineer”

}

15. What is a query parameter?
    Parameters passed after ? in the URL.
    
16. What is a path parameter?
    Dynamic value in the endpoint path.
    
17. What is pagination?
    Splitting large responses into multiple pages.
    
18. What is API versioning?
    Managing changes using /v1, /v2, headers.
    
19. What is idempotency?
    Multiple identical requests produce the same result.
    
20. What is caching in REST APIs?
    Storing responses to reduce server load.
    

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Manual API Testing with Postman

21. What is Postman?
    Postman is a tool used for manual and automated API testing.
    
22. What is a Postman collection?
    A group of related API requests.
    
23. What is a Postman environment?
    A set of variables for different environments (QA, staging, prod).
    
24. What are environment variables?
    Dynamic values used across requests.
    
25. How do you validate response manually in Postman?
    By checking status code, response body, and headers.
    
26. How do you test headers in Postman?
    Verify Content-Type, Authorization, and custom headers.
    
27. How do you test negative scenarios manually?
    Invalid payloads, missing headers, wrong endpoints.
    
28. What is API chaining?
    Using response data from one API in another request.
    
29. How do you handle authentication APIs manually?
    By passing tokens, API keys, or basic auth headers.
    
30. What is Newman?
    A command-line tool to run Postman collections (basic awareness).
    

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SOAP & XML Interview Questions

31. What is SOAP?
    A protocol for exchanging XML-based messages.
    
32. What is WSDL?
    XML file describing SOAP services.
    
33. How do you test SOAP APIs manually?
    Send XML requests and validate XML responses.
    

<response>

  <status>SUCCESS</status>

</response>

34. How do you validate XML response?
    By checking nodes, values, and schema.
    

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HTTP Status Codes – Must Know for Interviews

Code	Meaning
200	OK
201	Created
204	No Content
400	Bad Request
401	Unauthorized
403	Forbidden
404	Not Found
409	Conflict
500	Internal Server Error

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Real-Time API Validation Example (Manual Testing)

Request

POST /api/users

Payload

{

  “email”: “test@example.com”,

  “password”: “Test@123”

}

Response

{

  “id”: 501,

  “message”: “User created successfully”

}

Manual Validations

• Status code = 201
  
• id should not be null
  
• Message text is correct
  

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Automation Awareness (Interview Advantage)

Even for manual roles, interviewers like basic awareness of automation tools.

Postman Scripts (Basic)

pm.response.to.have.status(201);

SoapUI (Overview)

• JSONPath assertions
  
• XPath assertions
  
• Mock services
  

Rest Assured (Java – Awareness)

given().when().get(“/users/101”).then().statusCode(200);

Python Requests (Awareness)

import requests

assert requests.get(url).status_code == 200

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Scenario-Based API Manual Testing Questions (10+)

41. API returns 200 but incorrect data—what do you do?
    Validate business rules and log a defect.
    
42. How do you test authentication manually?
    Valid, invalid, and expired tokens.
    
43. How do you test rate limiting manually?
    Send multiple rapid requests and expect 429.
    
44. How do you test missing headers?
    Remove headers and validate error response.
    
45. How do you test invalid payload fields?
    Wrong data types, missing mandatory fields.
    
46. How do you test dependent APIs?
    Chain requests using response values.
    
47. How do you test file upload APIs manually?
    Validate size, format, and response message.
    
48. How do you test backward compatibility?
    Test older API versions.
    
49. How do you debug API failures?
    Check request, headers, payload, and response.
    
50. How do you test API performance manually?
    Measure response time using Postman.
    

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How Interviewers Evaluate Your Answers

Interviewers assess:

• Understanding of API fundamentals
  
• Ability to explain manual testing steps
  
• Knowledge of status codes
  
• Real-time problem-solving skills
  
• Clear and structured explanations
  

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API Manual Testing Cheat Sheet (Quick Revision)

• Validate status code + response body
  
• Test positive & negative cases
  
• Check headers and payload
  
• Verify business logic
  
• Use Postman efficiently
  
• Log defects with request/response
  

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FAQs – API Manual Testing Interview Questions

Q1. Is automation mandatory for API testing roles?
No, but basic awareness is helpful.

Q2. Is Postman enough for manual API testing?
Yes, Postman is widely used for manual testing.

Q3. Do freshers get API manual testing jobs?
Yes, strong fundamentals are enough.

Q4. Are REST APIs more important than SOAP?
Yes, REST is more commonly used today.