API testing is a must-have skill for testers and developers working with modern applications. It guarantees that APIs work correctly, return the expected data, and handle errors properly. In interviews, you’ll face questions about request types, response codes, authentication, and automation tools. This guide covers 40+ API testing interview questions with answers to help you prepare.
These questions will give you a solid understanding of real-world API testing challenges and best practices.
Fun Fact: The API testing market is expected to grow fast, with a 20.99% yearly rise from 2025 to 2034. By 2034, it could reach $27.38 billion.
Basic API Testing Interview Questions
Here is a list of basic API testing interview questions and answers:
- What is API testing, and why is it important?
API testing checks if an API works as expected by sending requests and verifying responses. It focuses on functionality, security, performance, and error handling. Since APIs connect different systems, testing helps catch issues early, reducing failures in production. It also confirms that responses contain correct data and handle errors properly.
- How is API testing different from UI testing?
API testing focuses on backend logic, data exchange, and response validation, while UI testing checks visual elements and user interactions. UI tests require a front-end, but API tests work without one. API tests are faster and more stable since they don’t rely on page structure. They also catch deeper issues that UI tests might miss.
- What are the key components of an API request and response?
An API request has:
- Method (GET, POST, PUT, DELETE)
- URL (endpoint location)
- Headers (metadata like content type, authentication)
- Body (data sent with POST/PUT)
An API response includes:
- Status code (e.g., 200 for success, 400 for bad request)
- Headers (response metadata)
- Body (returned data, usually in JSON or XML)
- What HTTP methods are commonly used in API testing?
Common HTTP methods include:
- GET – Fetches data
- POST – Sends data to create a resource
- PUT – Updates a resource
- PATCH – Partially updates a resource
- DELETE – Removes a resource
Each method performs a specific function and is tested to confirm proper behaviour.
API Testing Interview Questions for Freshers
Here are some common API testing questions for interview for freshers:
- What is the difference between SOAP and REST APIs?
SOAP (Simple Object Access Protocol) is a strict protocol using XML, with built-in security and reliability. REST (Representational State Transfer) is more flexible, using JSON or XML, and works over HTTP. REST is widely used in web applications due to its simplicity and scalability, while SOAP is used in enterprise systems needing strict security.
- How do you validate API response codes?
“I check if the status code matches expectations. For example, a successful request should return 200 OK, while an unauthorized request should return 401 Unauthorized. If the response doesn’t match expected codes, I debug using logs or API documentation. Automated scripts can validate status codes in test cases.”
- What is the purpose of headers in an API request?
Headers send extra information with requests and responses. Common headers include:
- Authorization – API keys or tokens for security
- Content-Type – Defines data format (e.g., JSON, XML)
- Accept – Specifies expected response format
- Cache-Control – Controls data caching behaviour
Headers help APIs process requests correctly and securely.
- Can APIs be tested manually? If so, how?
“Yes, I test APIs manually using tools like Postman or cURL. I send requests, check responses, and validate data. For example, I might send a GET request to fetch user data and verify if the returned details match expectations. Manual testing helps explore APIs before automating tests.”
Also Read - Top 50+ REST API Interview Questions and Answers
API Testing Interview Questions for Experienced
Let’s go through important API interview questions for experienced candidates.
We have categorized the questions as per the experience-level to make the preparation even easier for you.
API Testing Interview Questions for 1 Year Experience
If you have around 1 year of experience, you might come across such API testing questions for interview:
- What tools have you used for API testing?
“I have used Postman for manual testing, sending requests, and validating responses. For automation, I have worked with Rest Assured and Newman (Postman CLI). I have also used JMeter for performance testing and Swagger for API documentation testing.”
- How do you handle authentication in API testing?
“I test APIs using different authentication methods like API keys, OAuth, JWT, and Basic Auth. In Postman, I pass authentication tokens in the Authorization header. For automated tests, I fetch tokens dynamically and include them in requests.”
Also Read - Top 20 JMeter Interview Questions and Answers
API Testing Interview Questions for 2 Years’ Experience
Here are some common interview questions API testing for candidates with 2 years of experience:
- What is payload in an API request?
Payload is the actual data sent in a request body, usually in JSON or XML format. It is used in POST, PUT, and PATCH requests to send structured data, like user details in a signup API.
- How do you check API performance?
“I check response time, latency, and throughput using tools like JMeter, Postman, or K6. I also test API behaviour under high loads and track response times for different requests.”
API Testing Interview Questions for 3 Years’ Experience
If you have around 3 year of experience, you might come across such API testing questions for interview:
- How do you handle dynamic values in API automation?
“I extract dynamic values like tokens, timestamps, and session IDs from responses and store them in variables. In tools like Rest Assured or Postman, I use scripting to capture and reuse them in subsequent requests.”
- What are the most common API security vulnerabilities?
Common vulnerabilities include SQL injection, broken authentication, improper access control, and insecure data transmission. APIs should use HTTPS, token-based authentication, and proper input validation to prevent attacks.
API Testing Interview Questions for 4 Years’ Experience
Here are some common interview questions on API testing for candidates with 5 years of experience:
- How do you test APIs with different status codes?
“I send requests with different inputs and headers to trigger responses like 200 (OK), 400 (Bad Request), 401 (Unauthorized), 403 (Forbidden), and 500 (Internal Server Error). I also validate error messages and response handling.”
- How do you validate data consistency across multiple API calls?
“I compare API responses over time to detect mismatches. For example, after creating a user with a POST request, I verify it with a GET request. If APIs interact, I track data across services to check consistency.”
API Testing Interview Questions for 5 Years’ Experience
These are some API testing interview questions and answers for 5 years experienced candidates:
- What is contract testing in APIs?
Contract testing verifies that an API follows the agreed structure (schema). It checks if request/response formats, data types, and endpoints remain unchanged, preventing breaking changes in integrations.
- How do you mock an API for testing?
“I use tools like WireMock, Postman Mock Server, or Mountebank to create a simulated API. Mocks return predefined responses, allowing testing when the real API is unavailable or still in development.”
API Testing Interview Questions for 6 Years’ Experience
Here are some common interview questions on API testing for candidates with 6 years of experience:
- How do you handle API rate limits in testing?
“I send controlled requests within the allowed limit and test how the API behaves when the limit is exceeded. I verify if it returns 429 Too Many Requests and check how retries or backoff strategies work.”
- How do you approach API testing in microservices architecture?
“I test individual services (unit testing), their interactions (integration testing), and system behaviour (end-to-end testing). I also use contract testing to confirm compatibility between microservices.”
Also Read - Top 25 Spring Boot Microservices Interview Questions with Answers
API Testing Interview Questions for 7 Years’ Experience
Let’s go through common API testing interview questions for testers with 7 years of experience:
- What are some challenges in API automation, and how do you solve them?
“Challenges include handling authentication, managing dynamic data, and maintaining test scripts as APIs evolve. I solve these by using token-based authentication, implementing dynamic data extraction, and structuring test cases to be modular and reusable.”
- How do you integrate API tests into CI/CD pipelines?
“I integrate API tests using tools like Jenkins, GitHub Actions, or GitLab CI/CD. Automated scripts trigger API tests after deployments. If tests fail, the pipeline stops further releases. I also generate test reports to track failures.”
Also Read - Top 45+ Jenkins Interview Questions and Answers
API Testing Scenario Based Interview Questions
Here are common scenario-based API testing interview questions answers:
- An API returns 500 errors intermittently. How would you debug this?
“I check server logs, identify patterns in failures, and examine request payloads. If the issue is inconsistent, I analyze load conditions, database queries, and external dependencies. Running tests in different environments helps narrow down the cause.”
- How would you test an API with multiple dependent services?
“I test individual APIs first, then validate their interactions. I use mocking for unavailable services and conduct integration tests to verify real-time data exchange. End-to-end testing confirms that services work together without breaking.”
- An API response time suddenly increases. What steps would you take to investigate?
“I first check if the network or server is overloaded. Then, I inspect database queries, caching mechanisms, and third-party API calls. Performance testing with tools like JMeter or K6 helps identify bottlenecks.”
API Testing Real Time Interview Questions
You might also come across tricky interview questions on API testing like these:
- How do you handle APIs that return paginated responses?
“I verify that pagination works correctly by testing different page sizes, offsets, and navigation limits. I also check that responses maintain data consistency and that queries return the correct total number of results.”
- What would you do if an API request fails in a production environment?
“I check logs, error messages, and monitoring tools like Datadog or New Relic to find the root cause. If the issue is client-side, I validate the request format. If it’s server-side, I escalate it based on the severity.”
API Troubleshooting Interview Questions
Here are some questions on API testing about troubleshooting:
- How do you troubleshoot an API that returns incorrect data?
“I compare expected vs. actual responses and check if the request parameters, database queries, or transformations are incorrect. I also verify if caching issues are serving outdated data.”
- What steps do you take when an API suddenly stops working?
“I check server logs, API gateway errors, authentication failures, and rate limits. If external dependencies are involved, I verify if they are experiencing downtime. Testing in different environments helps isolate the issue.”
API Automation Testing Interview Questions
Let’s go through API automation interview questions and answers:
- What frameworks have you used for API automation?
This is one of the most common API automation interview questions for experienced candidates.
“I have worked with Rest Assured (Java), Postman (Newman CLI), Cypress (JavaScript), and Karate. These tools help automate functional and regression testing of APIs.”
- How do you handle dynamic response values in automated tests?
I extract values like tokens, timestamps, and user IDs using JSON path or XML parsers and store them in variables for reuse. This ensures tests remain stable despite dynamic data.
- How do you validate API responses in automated scripts?
I compare responses against expected status codes, response times, and schema validations. I use assertion libraries in JUnit, TestNG, or Chai to confirm correctness.
API Testing Interview Questions for Testers
Here are commonly-asked API interview questions for testers:
- What is the difference between functional and non-functional API testing?
Functional API testing checks whether the API performs expected actions, like returning correct data for a request. It includes validating request-response flows, status codes, and input handling.
Non-functional API testing focuses on performance, security, scalability, and reliability. It tests how the API behaves under high load, stress, or security attacks.
- How do you handle API request dependencies in testing?
“I identify dependent requests and execute them in the correct sequence. For example, if a test requires a user ID, I first create a user via a POST request and extract the ID for further tests. I also use mocking to simulate dependent services when they are unavailable.”
- What factors do you consider when designing API test cases?
“I consider the endpoint, request method, input parameters, authentication type, expected response, and possible error scenarios. I write test cases for positive, negative, boundary, and security testing to check how the API handles different conditions.”
- How do you check the correctness of API responses?
“I validate:
- Status codes (e.g., 200 for success, 400 for bad request)
- Response body (matching expected values)
- Data format (JSON, XML)
- Schema validation (using JSON schema validation tools)
- Error handling (checking if incorrect inputs return the right error messages)”
Note: API testing interview questions for testers often include topics like authentication, error handling, response validation, automation frameworks, and performance testing.
API Manual Testing Interview Questions
These are some important manual API testing interview questions and answers:
- What steps do you follow to manually test an API?
- Understand the API documentation (endpoints, request types, headers).
- Use Postman or cURL to send requests.
- Test different input parameters (valid, invalid, missing).
- Validate responses (status codes, data correctness, headers).
- Check API security (unauthorized access, SQL injection).
- Monitor response time and performance.
- How do you validate API responses using tools like Postman?
“In Postman, I:
- Send API requests with required parameters and headers.
- Verify response codes (e.g., 200 for success, 404 for not found).
- Check the response body for expected values.
- Use Postman tests (JavaScript assertions) to automate validation, like checking if a key exists in the response.”
REST API Testing Interview Questions
Here is a list of common RESTful API questions and answers:
- What are RESTful principles, and why are they important?
RESTful APIs follow six principles:
- Statelessness – Each request is independent; no client session is stored.
- Client-Server – The frontend and backend remain separate.
- Cacheability – Responses can be cached to improve performance.
- Uniform Interface – Consistent structure for endpoints and resources.
- Layered System – APIs can have multiple layers (e.g., security, caching).
- Code on Demand (optional) – The server can send executable code to the client.
Following these principles makes APIs scalable, maintainable, and easy to integrate. - What is the difference between PUT and PATCH methods?
- PUT updates a resource entirely, replacing all existing data.
- PATCH applies a partial update, modifying only specified fields.
Example: Updating a user profile: - PUT: Send full user details, including unchanged fields.
- PATCH: Send only the fields that need to be updated.
- How do you test a REST API without a user interface?
“I use Postman, cURL, or REST-assured to send direct API requests. I validate responses based on status codes, data correctness, headers, and performance. I also check authentication, rate limits, and error handling.”
- How do you automate REST API testing using Postman or another tool?
You might also come across REST API automation interview questions like this one.
“I create automated test collections in Postman using JavaScript test scripts. I write assertions to verify status codes, response time, and response body. Then, I run the tests using Newman (Postman CLI) for CI/CD integration. For large-scale automation, I use Rest Assured (Java) or Cypress (JavaScript).”
Also Read - Top 20+ Postman Interview Questions and Answers
REST Assured API Automation Testing Interview Questions
Let’s go through common REST Assured API automation testing interview questions and answers:
- What is REST Assured, and how does it work?
REST Assured is a Java library for testing REST APIs. It simplifies API automation by allowing requests and assertions in a single script. It supports:
- GET, POST, PUT, DELETE requests.
- JSON/XML validation.
- Authentication handling (OAuth, API keys).
- Schema validation for structured responses.
Example:
given().header(“Authorization”, “Bearer token”)
.when().get(“https://api.example.com/users”)
.then().statusCode(200);
- How do you validate JSON responses in REST Assured?
“I use JSONPath to extract values and validate them in test scripts.
Example:
given()
.when().get(“https://api.example.com/users/1”)
.then()
.body(“name”, equalTo(“John Doe”))
.body(“email”, containsString(“@”));
This verifies that the name is “John Doe” and the email contains “@”.”
Company-Specific API Testing Interview Questions
Capgemini API Testing Interview Questions
- What experience do you have with Selenium?
- Have you used Cucumber in any projects before?
- What is your experience working with RESTApi?
- What are some basic concepts of using Rest Assured?
- What API testing challenges have you faced in your projects?
Infosys API Testing Interview Questions
- What is BDD?
- What are new feature in Selenium 4?
- How do you test APIs that involve multiple integrations?
- How do you write test cases for a new API feature?
Accenture API Testing Interview Questions
- What is an API, and how does API testing differ from UI testing?
- Describe the different API testing methods.
- How do you test APIs for performance under high traffic?
- What strategies do you use to reduce API test execution time?
- How do you perform data-driven testing in API automation?
API Testing Interview Questions Amazon
- What are the key principles of good API design?
- What API testing tools are you familiar with?
- How do you test APIs that process large amounts of data?
- What API testing strategies would you use for a global e-commerce platform?
- How do you handle API versioning in testing?
Cognizant API Testing Interview Questions
- Which is a best technique to generate automated test report?
- How do you simulate network failures while testing an API?
- How do you handle API testing in cloud-based applications?
- What best practices do you follow when writing API test scripts?
API Testing MCQs
Here are some important API testing questions and answers in MCQ form:
- Which HTTP status code represents a successful GET request?
a) 200
b) 201
c) 400
d) 500
Answer: 200
- What is the purpose of an API key?
a) Encrypt data
b) Authenticate requests
c) Improve performance
d) Reduce latency
Answer: Authenticate requests
- Which tool is commonly used for API automation testing?
a) JIRA
b) Postman
c) Selenium
d) Jenkins
Answer: Postman
- What does the HTTP 401 status code mean?
a) Not Found
b) Unauthorized
c) Bad Request
d) Internal Server Error
Answer: Unauthorized
- Which of the following is NOT a valid HTTP method?
a) GET
b) POST
c) RUN
d) DELETE
Answer: RUN
Also Read - Top 45 Quality Assurance Interview Questions and Answers
Wrapping Up
And that’s a wrap on the top 40+ API testing interview questions and answers. Preparing for these questions will help you confidently tackle API testing interviews at any experience level. Keep practising with real scenarios and automation tools.
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