API Testing Interview Questions for Freshers

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Introduction: Growing Fresher Hiring Demand in Testing

With the rapid growth of web applications, mobile applications, cloud computing, and microservices architecture, API testing has become one of the most in-demand skills for software testing freshers. Modern applications rarely work as standalone systems. Instead, they consist of multiple services that communicate with each other through Application Programming Interfaces (APIs). 

Almost every industry—including e-commerce, banking, healthcare, travel, education, and finance—relies heavily on APIs to exchange data between applications. Because APIs are the backbone of modern software systems, companies actively hire freshers who understand basic API concepts, testing principles, and real-world testing scenarios. 

Many beginners believe that API testing requires advanced programming knowledge. However, this is a common misconception. For entry-level positions, interviewers generally focus on your understanding of API concepts, logical thinking, and testing approach rather than your coding skills. 

Preparing common API testing interview questions for freshers helps candidates build confidence and perform well during interviews, even if they have no prior industry experience. 

Why API Testing Is in High Demand 

API testing has become an essential part of software quality assurance because applications depend on APIs to exchange information quickly and accurately. 

Some of the major reasons API testing is highly valued include: 

  • Modern applications communicate through APIs.  
  • APIs enable communication between different software systems.  
  • API testing identifies defects before they affect the user interface.  
  • Faster API validation improves software quality.  
  • API testing supports Agile and DevOps development practices.  
  • Organizations increasingly expect testers to understand basic API concepts.  

What Interviewers Expect from Freshers 

During API testing interviews, companies generally evaluate whether candidates understand the basic concepts rather than expecting advanced technical expertise. 

Interviewers typically assess: 

  • Basic understanding of APIs.  
  • Knowledge of requests and responses.  
  • Ability to validate API behavior.  
  • Logical thinking and analytical skills.  
  • Understanding of common HTTP methods and status codes.  
  • Basic awareness of API testing tools.  
  • Willingness to learn automation in the future.  

This article explains API testing step by step using simple language, practical examples, sample test cases, and sample bug reports, making it ideal for students, fresh graduates, and beginners preparing for API testing interviews. 

What Is Software, Manual, and Automation Testing? (Simple Explanation) 

Before learning API testing, it is important to understand the basic concepts of software testing, manual testing, and automation testing because API testing combines knowledge from all three areas. 

What Is Software Testing? 

Software Testing is the process of verifying whether a software application works correctly according to the specified business requirements and user expectations. 

The objective of software testing is to identify defects before the application is released so that users receive a reliable, secure, and high-quality product. 

Testing compares the actual behavior of the application with the expected behavior to ensure that every feature performs correctly. 

Example 

Suppose an application has a login feature. 

A user enters a username and password. 

  • If the credentials are correct, the user should log in successfully.  
  • If the credentials are incorrect, the application should display an appropriate error message.  

If the application allows users to log in with an incorrect password, it is considered a defect. Software testing helps identify and fix such issues before the application reaches customers. 

Why Software Testing Is Important 

Software testing provides several important benefits: 

  • Finds defects before software is released.  
  • Improves software quality.  
  • Reduces maintenance costs.  
  • Ensures customer satisfaction.  
  • Verifies business requirements.  
  • Increases application reliability.  

What Is Manual Testing? 

Manual Testing is the process of testing software without using automation tools or scripts. Testers manually execute test cases, interact with the application, compare actual results with expected results, and report any defects they identify. 

Manual testing is the foundation of software testing because it helps testers understand application functionality, business logic, and user behavior. 

Examples of Manual Testing 

Some common manual testing activities include: 

  • Checking API responses manually using API testing tools.  
  • Verifying that error messages are displayed correctly.  
  • Validating response data.  
  • Testing different input combinations.  
  • Comparing expected and actual results.  
  • Reporting defects.  

Manual testing develops logical thinking and analytical skills that are essential for API testing. 

Manual testing is the foundation for API testing freshers. 

A strong understanding of manual testing concepts makes learning API testing much easier. 

What Is Automation Testing? 

Automation Testing is the process of executing software test cases using automation tools or scripts instead of performing the same actions manually every time. 

Automation testing is particularly useful for repetitive testing tasks such as regression testing, smoke testing, and repeated API validation. 

Simple Example 

Imagine that an API needs to be tested hundreds of times during every software release. 

Instead of manually sending the same API request repeatedly: 

  • Write an automation script once.  
  • Execute the script automatically whenever required.  

Automation saves time, reduces manual effort, and improves testing consistency. 

Benefits of Automation Testing 

Automation testing offers several advantages, including: 

  • Faster execution of repetitive tests.  
  • Reduced manual effort.  
  • Improved testing accuracy.  
  • Reusable test scripts.  
  • Better regression testing.  
  • Faster software delivery.  

For freshers, understanding automation concepts is more important than mastering automation tools or writing complex scripts. 

What Is API Testing? (For Beginners) 

API Testing is the process of verifying whether an Application Programming Interface (API) functions correctly by sending requests to the API and validating the responses it returns. 

Instead of testing the application’s graphical user interface, API testing focuses on the communication that occurs between different software components. 

API testing verifies that the backend services work correctly before data is displayed on the user interface. 

What Is an API? 

An API (Application Programming Interface) is a set of rules that allows two software systems to communicate and exchange information with each other. 

Whenever one application needs information from another application, it sends a request through an API, and the receiving application returns an appropriate response. 

APIs enable modern applications to share data securely and efficiently. 

Simple Explanation 

Consider a mobile banking application. 

When a user logs in: 

  1. The user enters a username and password on the application’s user interface.  
  1. The UI sends a login request to the API.  
  1. The API verifies the credentials using the backend database.  
  1. The API processes the request.  
  1. The API returns a response indicating whether the login was successful or unsuccessful.  
  1. The UI displays the appropriate message to the user.  

The API acts as the communication bridge between the frontend application and the backend server. 

What Does API Testing Check? 

During API testing, testers validate multiple aspects of the API to ensure it behaves correctly. 

API testing typically verifies: 

  • Requests are sent with the correct data.  
  • Responses are returned correctly.  
  • Data accuracy matches business requirements.  
  • Error handling works correctly for invalid requests.  
  • HTTP status codes are appropriate.  
  • Response time meets performance expectations.  
  • Security requirements are satisfied.  
  • Response structure is correct.  

Why Is API Testing Important? 

API testing is an important part of modern software testing because many applications depend on APIs for communication. 

Major benefits of API testing include: 

  • Detects backend defects before UI testing begins.  
  • Faster execution than UI testing.  
  • Improves software quality.  
  • Ensures correct data exchange between systems.  
  • Supports continuous testing in Agile and DevOps.  
  • Reduces testing effort by identifying issues early.  

Understanding these API testing fundamentals provides freshers with a strong foundation for answering API testing interview questions and preparing for real-world software testing projects. 

API Testing Interview Questions for Freshers (With Answers) 

Below are 60+ api testing interview questions for freshers, starting from very basic to slightly advanced. 

Basic API Testing Interview Questions  

1. What is an API? 

An API (Application Programming Interface) is a set of rules that allows two or more software applications to communicate with each other and exchange data. 

Instead of accessing the database directly, applications send requests to an API, which processes those requests and returns the required information. 

Example 

When you log in to a shopping application: 

  • The application sends your username and password to the login API.  
  • The API verifies your credentials.  
  • The API returns a response indicating whether the login was successful or unsuccessful.  

APIs act as a bridge between the frontend (user interface) and the backend (server and database). 

2. Why is API Testing Important? 

API Testing is important because it verifies that backend services work correctly before the data reaches the user interface. It helps identify issues early in the development cycle and ensures reliable communication between software systems. 

Benefits of API Testing 

  • Ensures data accuracy.  
  • Improves system reliability.  
  • Detects defects early.  
  • Verifies business logic.  
  • Supports faster testing.  
  • Improves software quality.  
  • Reduces UI-related testing effort.  

Since APIs are used by web applications, mobile applications, and third-party services, testing them is essential. 

3. What is an API Request? 

An API Request is a message sent by a client application to a server asking for data or requesting an action to be performed. 

Every request typically contains: 

  • HTTP method  
  • Endpoint (URL)  
  • Headers  
  • Parameters  
  • Request body (if required)  

Example 

A login request sends the username and password to the server for authentication. 

4. What is an API Response? 

An API Response is the reply sent by the server after processing an API request. 

The response usually contains: 

  • HTTP status code.  
  • Response body.  
  • Response headers.  
  • Error messages (if any).  

The response informs the client whether the request was successful or unsuccessful. 

5. What are Common API Methods? 

HTTP methods define the type of operation that should be performed on a resource. 

Common API Methods 

  • GET – Retrieves data from the server.  
  • POST – Creates new data on the server.  
  • PUT – Updates existing data.  
  • DELETE – Removes data from the server.  

These methods form the foundation of REST API communication. 

Freshers QA Interview Q&A – API Basics 

6. What is REST API? 

REST (Representational State Transfer) API is an architectural style used for building web services. 

REST APIs communicate over HTTP and use methods such as GET, POST, PUT, and DELETE to perform operations. 

Advantages of REST APIs 

  • Lightweight.  
  • Fast.  
  • Easy to understand.  
  • Widely used.  
  • Supports JSON responses.  

Most modern web and mobile applications use REST APIs. 

7. What is SOAP API? 

SOAP (Simple Object Access Protocol) is a protocol used for exchanging structured information between applications. 

SOAP APIs use XML messages and follow strict communication standards. 

They are commonly used in industries where high security and reliability are required, such as banking and healthcare. 

8. Difference Between REST and SOAP? 

REST and SOAP are two different approaches for building web services. 

REST API SOAP API 
Lightweight More secure but complex 
Uses JSON (commonly) Uses XML 
Faster performance More processing overhead 
Easy to develop Strict protocol-based communication 
Widely used in modern applications Common in enterprise systems 

Freshers should understand the basic differences rather than memorizing technical details. 

9. What is an Endpoint? 

An Endpoint is a specific URL where API requests are sent. 

Each endpoint performs a particular operation. 

Example 

  • /login  
  • /users  
  • /products  
  • /orders  

Different endpoints provide access to different application features. 

10. What is Payload? 

A Payload is the actual data sent in an API request or received in an API response. 

For example, during login, the payload may contain: 

  • Username  
  • Password  

The server processes this payload and returns an appropriate response. 

Manual API Testing Interview Questions 

11. How Do You Test an API Manually? 

Manual API testing is performed by sending requests to an API and validating the responses without writing automation scripts. 

A commonly used tool for manual API testing is Postman. 

Steps to Test an API Manually 

  1. Open the API testing tool.  
  1. Select the required HTTP method.  
  1. Enter the endpoint URL.  
  1. Add headers if required.  
  1. Enter request data.  
  1. Send the request.  
  1. Verify the status code.  
  1. Validate the response body.  
  1. Check response time.  
  1. Verify error handling.  

12. What is a Status Code? 

A Status Code is a three-digit HTTP number returned by the server that indicates the result of an API request. 

Status codes help testers determine whether the request was processed successfully or failed. 

13. Common HTTP Status Codes? 

Some of the most frequently used HTTP status codes include: 

  • 200 OK – Request completed successfully.  
  • 400 Bad Request – Invalid request sent by the client.  
  • 401 Unauthorized – Authentication failed.  
  • 404 Not Found – Requested resource does not exist.  
  • 500 Internal Server Error – Unexpected server-side error.  

Understanding these status codes is essential for API testing interviews. 

14. What is a Header in API? 

An API Header contains additional information (metadata) about the request or response. 

Headers commonly include: 

  • Authentication tokens.  
  • Content-Type.  
  • Accept.  
  • Authorization.  
  • Language preferences.  

Headers help the server understand how the request should be processed. 

15. What is JSON? 

JSON (JavaScript Object Notation) is a lightweight and easy-to-read format used to exchange data between applications. 

Most REST APIs return responses in JSON format. 

Example 

{ 
 “username”: “john”, 
 “status”: “Success” 
} 

JSON is widely used because it is simple, readable, and supported by most programming languages. 

Simple Automation Interview Questions for API Testing 

16. Can API Testing Be Automated? 

Yes. API testing can be automated using specialized tools and frameworks. 

Common tools include: 

  • Postman  
  • Rest Assured  
  • Newman  
  • SoapUI  

Automation allows API test cases to be executed repeatedly, making regression testing faster and more efficient. 

17. Is Coding Mandatory for API Testing? 

Advanced programming knowledge is not mandatory for beginners learning API testing. 

However, basic scripting knowledge helps when automating API tests. 

For freshers, interviewers usually focus more on: 

  • API concepts.  
  • Request-response understanding.  
  • Logical thinking.  
  • Testing approach.  

18. What is a Collection in Postman? 

A Collection in Postman is a group of related API requests organized together. 

Collections help testers: 

  • Organize APIs.  
  • Execute multiple requests.  
  • Share APIs with team members.  
  • Perform automated collection runs.  

19. What is an Environment in Postman? 

An Environment in Postman stores variables that can be reused across multiple API requests. 

Common variables include: 

  • Base URL.  
  • Authentication token.  
  • Username.  
  • Password.  

Using environments makes API testing easier across Development, QA, and Production environments. 

20. What is a Token? 

A Token is a security credential used to authenticate and authorize users or applications. 

After successful login, many APIs generate a token that must be included in subsequent requests to access protected resources. 

Tokens improve application security by verifying user identity. 

Scenario-Based API Testing Questions for Freshers 

21. How Will You Test a Login API? 

When testing a login API, verify both positive and negative scenarios. 

Test Scenarios 

  • Send valid username and password.  
  • Send invalid username.  
  • Send invalid password.  
  • Leave required fields blank.  
  • Verify token generation after successful login.  
  • Validate the response message.  
  • Verify appropriate HTTP status codes.  
  • Check response time.  

Testing multiple scenarios ensures that the login API behaves correctly under different conditions. 

22. How Will You Test an Invalid API Request? 

To test an invalid API request: 

  1. Send incorrect or incomplete input data.  
  1. Verify that the server returns the correct error response.  
  1. Validate the HTTP status code.  
  1. Check whether the error message is meaningful.  
  1. Ensure the server handles invalid input gracefully without crashing.  

Negative testing verifies the robustness of the API. 

23. What If an API Returns Wrong Data? 

If the API returns incorrect data: 

  • Verify the request.  
  • Compare the response with the requirement.  
  • Capture request and response details.  
  • Record the status code.  
  • Log a detailed defect.  

Providing complete evidence helps developers investigate the issue quickly. 

24. How Do You Test API Performance? 

API performance testing verifies whether the API responds within acceptable time limits under different workloads. 

Typical checks include: 

  • Response time.  
  • Concurrent user load.  
  • Throughput.  
  • Server stability.  
  • Performance under peak traffic.  

Fast and consistent API responses improve overall application performance. 

25. How Do You Validate API Security? 

API security testing verifies that unauthorized users cannot access protected resources. 

Common security checks include: 

  • Unauthorized access attempts.  
  • Invalid authentication tokens.  
  • Expired tokens.  
  • Missing authentication headers.  
  • Access to restricted endpoints.  

Security testing helps protect sensitive application data. 

Sample Test Cases for Freshers 

Login API Test Case Example 

A login API is one of the most frequently tested APIs because it controls user authentication. 

Sample Login API Test Case 

Field Details 
Test Case ID TC_API_Login_01 
Scenario Verify login with valid credentials. 
Request Method POST 
Input Valid username and password. 
Expected Result The API should return HTTP Status Code 200 and generate a valid authentication token. 
Status Pass 

Additional Login API Test Scenarios 

  • Verify login with an invalid password.  
  • Verify login with an invalid username.  
  • Verify login with blank credentials.  
  • Verify login with missing mandatory fields.  
  • Verify token expiration.  
  • Verify invalid authentication tokens.  

Mobile App API Test Case Example 

Mobile applications frequently use APIs to retrieve product information, user profiles, and order details. 

Scenario: Verify Product List API 

Test Steps 

  1. Send a GET request to the Product List API.  
  1. Verify the HTTP response code.  
  1. Validate the number of products returned.  
  1. Verify response time.  
  1. Validate required response fields.  

Expected Results 

  • The API should return HTTP Status Code 200.  
  • Product count should match the database.  
  • Response structure should be correct.  
  • Response time should meet performance expectations.  

UI + API Test Case Example 

API testing and UI testing often work together to ensure consistency between backend services and frontend applications. 

Scenario: Verify UI Reflects API Data 

Test Steps 

  1. Call the required API.  
  1. Validate the API response.  
  1. Open the application UI.  
  1. Verify that the UI displays the same information returned by the API.  
  1. Confirm that no data is missing or incorrect.  

Expected Results 

  • API response should be correct.  
  • UI should display the same data.  
  • Data formatting should be accurate.  
  • No inconsistencies should exist between the API and UI.  

Bug Report Writing Examples for Freshers 

A bug report documents defects discovered during API testing. A clear and complete bug report helps developers reproduce and resolve issues efficiently. 

Sample API Bug Report 

Bug ID 

API_201 

Title 

Login API Returns Success for Invalid Password 

Environment 

QA 

Steps to Reproduce 

  1. Send a login API request using a valid username and an incorrect password.  
  1. Observe the API response.  

Expected Result 

The API should reject the request and return HTTP Status Code 401 (Unauthorized) with an appropriate error message. 

Actual Result 

The API returns HTTP Status Code 200 (Success), allowing authentication despite an invalid password. 

Severity 

High 

The issue affects authentication and poses a significant security risk. 

Status 

New 

The defect has been reported for investigation. 

Tips to Answer Confidently in API Testing Interviews 

Strong communication and logical thinking are just as important as technical knowledge during API testing interviews. 

Tips for Freshers 

  • Explain concepts using simple, real-world examples.  
  • Avoid using complex technical terms unnecessarily.  
  • Mention tools such as Postman or Rest Assured only when relevant.  
  • Focus on understanding the Request → Process → Response flow.  
  • Think from both the user’s perspective and the tester’s perspective.  
  • Explain your reasoning clearly instead of memorizing answers.  
  • Stay confident and communicate step by step.  

Interviewers usually value clarity, structured thinking, and problem-solving skills more than complicated technical explanations. 

Quick Revision Sheet (One-Glance Summary) 

Review these important concepts before attending an API testing interview. 

Concept Quick Revision 
API Connects different software systems and enables data exchange. 
API Flow Request → Process → Response. 
HTTP Status Codes Indicate whether the API request succeeded or failed. 
API Validation Verify data accuracy, error handling, response codes, response time, and security. 
Manual API Testing Foundation for understanding API behavior before automation. 

This quick revision sheet serves as a handy reference for refreshing core API testing concepts before interviews. 

FAQs – API Testing Interview Questions for Freshers 

Q1. Is API Testing Hard for Freshers? 

No. API testing becomes much easier once you understand the basic concepts such as requests, responses, HTTP methods, status codes, and JSON. With regular practice using tools like Postman, freshers can quickly build confidence in API testing. 

Q2. Do I Need Coding Knowledge? 

Advanced coding knowledge is not mandatory for beginners. Basic scripting knowledge is helpful for API automation, but interviewers usually focus on your understanding of API concepts, request-response flow, and logical problem-solving rather than programming expertise. 

Q3. Which Tool Is Best for Beginners? 

Postman is considered one of the best tools for beginners because it provides a simple interface for sending API requests, validating responses, organizing collections, and learning API testing concepts without requiring extensive programming knowledge. 

Q4. Is API Testing Manual or Automation? 

API testing can be performed using both manual and automation approaches. 

  • Manual API testing involves sending requests and validating responses using tools such as Postman.  
  • Automated API testing uses tools and frameworks such as Rest Assured, Newman, or SoapUI to execute API test cases repeatedly.  

Both approaches are widely used depending on project requirements. 

Q5. What Should Freshers Focus on First? 

Freshers should begin by learning the fundamentals of API testing, including API concepts, HTTP methods, status codes, requests, responses, JSON, endpoints, and authentication. After building a strong understanding of these basics, they should practice writing API test cases, executing requests in Postman, analyzing responses, and solving scenario-based interview questions before moving on to API automation. 

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