Top 30 Beginner API Interview Questions to Kickstart Your Journey

Are you a fresher or an entry-level professional preparing for an API-related interview? Whether you’re just starting out or looking to sharpen your skills, this guide will help you ace your API interviews. In this post, we’ll cover the fundamentals of API concepts, HTTP methods, and REST principles through 30 of the most common beginner-level API interview questions.

Top 30 Beginner API Interview Questions with Answers

1. What is an API, and why is it important in modern software development?
   An API (Application Programming Interface) is a set of rules and protocols that allows different software applications to communicate with each other. It defines the methods and data formats that applications use to exchange information. APIs are essential for enabling different services to interact seamlessly, such as linking a payment gateway to a website.
2. Can you explain the difference between REST and SOAP APIs?
   REST (Representational State Transfer) is an architectural style that uses standard HTTP methods like GET, POST, PUT, and DELETE. It is lightweight and suitable for web services. SOAP (Simple Object Access Protocol), on the other hand, is a protocol that relies on XML for communication and is more rigid and complex.
3. What are the main HTTP methods used in REST APIs?
   The main HTTP methods are:
   • GET: Retrieve data from the server.
   • POST: Send data to the server to create a new resource.
   • PUT: Update an existing resource on the server.
   • DELETE: Remove a resource from the server.
   • PATCH: Partially update a resource on the server.
4. How does the GET method work in an API request?
   The GET method is used to retrieve data from a server. It sends a request to a specific URL, and the server returns the requested data, usually in JSON or XML format.
5. What is the purpose of an API endpoint?
   An API endpoint is a specific URL where an API can access resources. Each endpoint is associated with a particular function (e.g., fetching user data, posting a comment).
6. What is JSON, and why is it commonly used in API responses?
   JSON (JavaScript Object Notation) is a lightweight data-interchange format that is easy for humans to read and write and easy for machines to parse and generate. It is commonly used in APIs due to its simplicity and compatibility with most programming languages.
7. What is an API key, and how does it function in API authentication?
   An API key is a unique identifier used to authenticate a client or application when accessing an API. It is passed along with the API request and verifies that the client has permission to access the resource.
8. What are status codes in API responses, and why are they important?
   Status codes are three-digit numbers returned by the server to indicate the result of an API request. Common examples include:
   • 200 OK: The request was successful.
   • 404 Not Found: The requested resource could not be found.
   • 500 Internal Server Error: The server encountered an error.
9. Can you explain what OAuth is and how it works in API security?
   OAuth is an open standard for access delegation commonly used for token-based authentication. It allows third-party applications to access user data without sharing the user’s credentials by issuing an access token.
10. What is the difference between PUT and PATCH in REST APIs?
    • PUT: Replaces the entire resource with a new one.
    • PATCH: Partially updates a resource, only modifying the fields that are specified in the request.
11. What is CORS (Cross-Origin Resource Sharing), and why is it used in APIs?
    CORS is a security feature implemented by browsers to prevent web pages from making requests to a different domain than the one that served the web page. It allows APIs to specify which origins are permitted to access their resources.
12. What is a Webhook, and how is it different from an API?
    A Webhook is a user-defined HTTP callback that allows one system to send real-time data to another system when a specific event occurs. Unlike APIs, which require the client to make a request, webhooks send data automatically when triggered.
13. What are the advantages of using REST over SOAP?
    REST is generally simpler, faster, and more flexible than SOAP. It uses standard HTTP methods, is more lightweight, and works with multiple data formats like JSON and XML, while SOAP relies solely on XML.
14. How would you handle versioning in a REST API?
    Versioning in REST APIs can be handled by including the version number in the API URL (e.g., /api/v1/resource) or in the request headers.
15. What is rate limiting, and why is it important in APIs?
    Rate limiting restricts the number of API requests a client can make within a specified time frame. This helps prevent abuse, ensures fair use, and protects the server from overloading.
16. Explain what an API response body is.
    The response body is the data sent by the server in response to an API request. It typically contains the requested information or an error message if the request fails.
17. What is a RESTful API?
    A RESTful API is an API that adheres to the principles of REST, using HTTP methods, statelessness, and standard conventions for accessing resources.
18. What is Swagger, and how is it used in API development?
    Swagger is a framework for documenting REST APIs. It provides an interactive interface for testing API endpoints and generating client code, helping developers design, document, and consume APIs more effectively.
19. What is the difference between a synchronous and asynchronous API?
    • Synchronous API: The client waits for a response before proceeding.
    • Asynchronous API: The client does not wait for a response and can continue with other tasks while the server processes the request.
20. What are headers in an API request?
    Headers contain metadata about the API request or response, such as authentication tokens, content type, and user-agent information.
21. What is API testing, and why is it important?
    API testing involves verifying that an API functions as expected, handles errors properly, and maintains security. It is crucial for ensuring the reliability and security of applications that depend on APIs.
22. How would you test the security of an API?
    API security testing includes checking for vulnerabilities like SQL injection, cross-site scripting (XSS), and ensuring proper authentication and authorization mechanisms are in place.
23. What is the difference between REST and GraphQL?
    REST is an architectural style that defines a set of rules for building APIs. GraphQL is a query language for APIs that allows clients to request specific data, reducing over-fetching or under-fetching of information.
24. What is a REST API status code 401?
    A status code of 401 means “Unauthorized.” It indicates that the request lacks valid authentication credentials.
25. What is an API rate limit, and how can it be handled?
    API rate limits specify the number of API calls a client can make in a given time frame. Handling it involves checking the limit and either delaying requests or notifying the user once the limit is reached.
26. What is an API Gateway?
    An API Gateway is a server that acts as an entry point for all incoming API requests. It routes requests to the appropriate microservices, handles load balancing, and can provide additional services like authentication and rate limiting.
27. What is the role of HTTP status code 503?
    HTTP status code 503 stands for “Service Unavailable.” It indicates that the server is temporarily unable to handle the request due to maintenance or overload.
28. What is JSON Schema?
    JSON Schema is a tool used to define the structure and validation rules for JSON data, ensuring that it is formatted correctly.
29. What is the difference between authentication and authorization in an API?
    • Authentication verifies the identity of a user or system.
    • Authorization determines what actions or resources the authenticated user can access.
30. What is an API client?
    An API client is a software or application that interacts with an API by sending requests and receiving responses. Examples include Postman or custom-built applications.

Conclusion

By mastering these 30 beginner-level API interview questions and answers, you’ll be well on your way to cracking your next API interview. Remember, consistent practice and hands-on experience with real-world APIs will only strengthen your understanding.

Call to Action

• Ready to dive deeper into API testing? Explore our Intermediate-Level API Questions here!
• Looking to automate API testing? Learn how to use Selenium for API Testing.