Introduction – Why API Testing Is Important in Interviews
For freshers entering the software testing field, API testing has become a must-have skill. Even entry-level QA roles now expect candidates to understand how applications work beyond the UI.
Interviewers ask api testing interview questions for freshers to check whether you:
- Understand how frontend and backend communicate
- Know basic REST API concepts
- Can validate responses and status codes
- Are familiar with tools like Postman or SoapUI
- Can think logically about real-world scenarios
The good news?
You don’t need deep automation or performance expertise as a fresher. Strong fundamentals, clear explanations, and basic hands-on knowledge are enough.
This article is written specifically for freshers, using simple language, practical examples, and interview-focused answers.
What Is API Testing? (Clear & Simple)
API testing is the process of testing Application Programming Interfaces to ensure they:
- Accept correct input
- Return correct output
- Follow business rules
- Handle errors properly
Unlike UI testing, API testing:
- Does not involve screens or buttons
- Works directly with requests and responses
Simple Example
For a Login API:
- Valid username & password → 200 OK
- Wrong password → 401 Unauthorized
- Missing username → 400 Bad Request
REST vs SOAP vs GraphQL (Beginner-Level Comparison)
| Feature | REST | SOAP | GraphQL |
| Protocol | HTTP | XML-based | HTTP |
| Data Format | JSON / XML | XML only | JSON |
| Complexity | Easy | Moderate | Moderate |
| Usage | Most modern apps | Banking / legacy | Modern apps |
👉 For freshers, REST API basics are most important. SOAP knowledge is a plus.
API Testing Interview Questions for Freshers (90+ Questions with Answers)
Section 1: Basic API Concepts (Q1–Q20)
1. What is an API?
An API allows two applications to communicate with each other.
2. What is API testing?
API testing verifies requests, responses, status codes, headers, and data.
3. Why is API testing important?
Because APIs connect systems, and one bug can affect many applications.
4. API testing vs UI testing?
API testing checks backend logic; UI testing checks frontend behavior.
5. What are common types of APIs?
REST and SOAP APIs.
6. What is REST?
A lightweight API architecture using HTTP.
7. What is SOAP?
An XML-based protocol used mostly in enterprise systems.
8. What is an endpoint?
A URL representing an API resource, e.g. /users/101.
9. What is request payload?
Data sent to the API.
10. What is response payload?
Data returned by the API.
11. What is statelessness?
Each API request is independent.
12. What is idempotency?
Repeating the same request gives the same result.
13. What is authentication?
Verifying user identity.
14. What is authorization?
Verifying what actions a user can perform.
15. What authentication types are common?
Basic Auth, Bearer Token, API Key.
16. What is JSON?
A lightweight data format used in REST APIs.
{
“id”: 101,
“name”: “Rahul”
}
17. What is XML?
A markup language used mainly in SOAP APIs.
<user>
<id>101</id>
<name>Rahul</name>
</user>
18. What is positive testing?
Testing with valid input.
19. What is negative testing?
Testing with invalid input.
20. What is API versioning?
Managing API changes using /v1, /v2.
HTTP Methods – Fresher Must-Know
| Method | Purpose |
| GET | Fetch data |
| POST | Create data |
| PUT | Update full data |
| PATCH | Update partial data |
| DELETE | Remove data |
HTTP Status Codes – Very Important for Freshers
| Code | Meaning | Example |
| 200 | OK | Successful GET |
| 201 | Created | Successful POST |
| 204 | No Content | Successful DELETE |
| 400 | Bad Request | Invalid input |
| 401 | Unauthorized | Invalid login |
| 403 | Forbidden | No permission |
| 404 | Not Found | Wrong URL |
| 500 | Server Error | Backend issue |
Section 2: API Testing Basics (Q21–Q45)
21. What validations are done in API testing?
Status code, response body, headers, and response time.
22. Is checking status code enough?
No, response data must also be validated.
23. What is header validation?
Checking headers like Content-Type and Authorization.
24. What is schema validation?
Validating response structure.
25. What is response time testing?
Checking how fast API responds.
26. What is smoke testing?
Basic API health check.
27. What is regression testing?
Re-testing APIs after changes.
28. What is API security testing?
Testing authentication and authorization.
29. What is API performance testing?
Testing speed and scalability.
30. What is pagination testing?
Testing page-wise data responses.
31. What is filtering testing?
Testing query parameters.
32. What is sorting testing?
Testing order of response data.
33. What is API chaining?
Using response from one API in another API.
34. What is API mocking?
Simulating API responses.
35. What is rate limiting?
Restricting number of API calls.
36. What is throttling?
Controlling traffic to protect backend.
37. What is boundary value testing?
Testing minimum and maximum values.
38. What is data consistency testing?
Ensuring same data across systems.
39. What is API rollback?
Ensuring no partial data saved on failure.
40. What is content-type validation?
Ensuring response format is JSON/XML.
41. What is API documentation?
Explains how to use the API.
42. What is Swagger/OpenAPI?
Tool for API documentation.
43. What is API contract?
Agreement between client and server.
44. What is concurrency testing?
Testing multiple users at the same time.
45. What is API caching?
Storing responses temporarily.
Real-Time API Validation Example (Fresher Level)
Request
POST /api/login
{
“username”: “testuser”,
“password”: “password123”
}
Response
{
“token”: “abc123”,
“expiresIn”: 3600
}
What to Validate
- Status code = 200
- Token is not null
- expiresIn > 0
Postman / SoapUI / Automation Basics for Freshers
Postman – Simple Test Script
pm.test(“Status code is 200”, function () {
pm.response.to.have.status(200);
});
SoapUI – XPath Assertion
//token != ”
Rest Assured (Awareness)
given().when().get(“/users/1”).then().statusCode(200);
Python Requests (Awareness)
import requests
res = requests.get(url)
assert res.status_code == 200
👉 As a fresher, basic awareness is enough.
Scenario-Based API Testing Interview Questions for Freshers (12)
- API returns 200 but wrong data – what do you check?
- API works in Postman but fails in application – why?
- Missing parameter returns 500 – is it correct?
- API allows access without token – what issue?
- Duplicate record created – what testing missed?
- API slow for large data – what test?
- API returns null values – how validate?
- Invalid input accepted – what defect?
- API returns wrong status code – impact?
- Same request gives different responses – why?
- Unauthorized user accesses data – issue?
- API fails only in production – possible reasons?
How Interviewers Evaluate Freshers’ Answers
Interviewers focus on:
- Clarity of basics
- Logical thinking
- Ability to explain examples
- Awareness of negative scenarios
- Confidence, not memorization
👉 Simple + clear answers score more than complex jargon.
API Testing Interview Cheatsheet for Freshers
- Understand REST basics
- Learn HTTP methods & status codes
- Validate response data
- Practice Postman daily
- Think about negative scenarios
- Don’t panic if you don’t know automation
FAQs – API Testing Interview Questions for Freshers
Q1. Is API testing mandatory for freshers?
Yes, basic API knowledge is expected.
Q2. Is Postman enough to start?
Yes, Postman is perfect for beginners.
Q3. Do freshers need automation skills?
Not mandatory, but awareness helps.
Q4. Biggest mistake freshers make?
Only checking status codes.
Q5. How to prepare in 1–2 weeks?
Practice simple REST APIs daily using Postman.