Web API Interview Questions and Answers

Ques 1. What is RESTful Web API?

RESTful Web API (Representational State Transfer) is an architectural style that uses standard HTTP methods (GET, POST, PUT, DELETE) for communication and relies on stateless, client-server interactions.

Example:

GET /users/1

Ques 2. Explain the difference between PUT and POST methods in HTTP.

PUT is used to update or create a resource if it doesn't exist, while POST is used to submit data to be processed to a specified resource.

Example:

PUT /users/1 {"name": "John"}

Ques 3. What is the purpose of the HTTP DELETE method?

The DELETE method is used to request the removal of a resource identified by the URI. It is often used to delete a resource on the server.

Example:

DELETE /users/1

Ques 4. What is CORS, and how does it affect Web API security?

CORS (Cross-Origin Resource Sharing) is a security feature implemented by web browsers to restrict webpages from making requests to a different domain than the one that served the original webpage. Web APIs need proper CORS configuration to allow or deny cross-origin requests.

Ques 5. Explain the concept of Idempotence in the context of Web APIs.

Idempotence means that a given operation will produce the same result regardless of how many times it is executed. In Web APIs, methods like GET, PUT, and DELETE are expected to be idempotent.

Ques 6. What is the purpose of the OPTIONS HTTP method?

The OPTIONS method is used to describe the communication options for the target resource. It is often used to support CORS preflight requests and provide information about the available methods for a resource.

Example:

OPTIONS /users

Ques 7. What is the role of HTTP status codes in Web APIs?

HTTP status codes indicate the success, failure, or other status of a request. Common codes include 200 OK (success), 404 Not Found (resource not found), and 500 Internal Server Error (server error).

Ques 8. Explain the concept of Pagination in Web APIs.

Pagination is the practice of dividing a large set of data into smaller, manageable parts (pages) to improve performance and user experience. It involves using query parameters like 'page' and 'pageSize' in API requests.

Example:

GET /users?page=1&pageSize=10

Ques 9. What is the purpose of the HEAD HTTP method?

The HEAD method is similar to GET but without the response body. It is used to retrieve metadata about a resource without transferring the actual data, which can be useful for checking resource availability or obtaining information about the server.

Example:

HEAD /users/1

Ques 10. Explain the difference between stateful and stateless communication in Web APIs.

Stateful communication involves the server remembering the state of the client, while stateless communication treats each request as an independent transaction. RESTful APIs are typically designed to be stateless, with each request containing all the information needed for processing.

Ques 11. Explain the purpose of the PATCH HTTP method.

PATCH is used to apply partial modifications to a resource. It is typically used when you want to update part of a resource without affecting the entire representation.

Example:

PATCH /users/1 {"name": "UpdatedName"}

Ques 12. What are the key differences between SOAP and RESTful Web Services?

SOAP (Simple Object Access Protocol) is a protocol for exchanging structured information in web services, whereas REST is an architectural style. SOAP uses XML for message formatting, while REST commonly uses JSON. RESTful services are generally considered simpler and more scalable.

Ques 13. Explain the concept of rate limiting in the context of Web APIs.

Rate limiting is a mechanism used to control the number of requests a client can make to an API within a specified time frame. It helps prevent abuse, ensure fair usage, and protect the server from overload.

Ques 14. What is the purpose of the ETag header in HTTP responses?

ETag (Entity Tag) is a mechanism for web caching and conditional requests. It provides a way for the server to tag a resource with a unique identifier, allowing clients to check if the resource has been modified since a certain time.

Ques 15. Explain the concept of content negotiation in Web APIs.

Content negotiation is the process of selecting the appropriate representation of a resource based on the client's preferences. It involves using headers like 'Accept' and 'Content-Type' to specify the desired format for data exchange.

Ques 16. What is the role of middleware in the context of Web API development?

Middleware refers to software components that can be inserted into the request-response processing pipeline to perform various functions such as authentication, logging, and input validation. It allows developers to customize the behavior of the application.

Ques 17. What is the purpose of the 'OPTIONS' HTTP request method?

The 'OPTIONS' method is used to describe the communication options for the target resource. It is often used to support preflight requests in CORS and to provide information about the available methods for a resource.

Example:

OPTIONS /users

Ques 18. Explain the concept of versioning in Web APIs and mention different approaches.

Versioning is the practice of managing changes to an API over time. Different approaches include URI versioning (e.g., /v1/users), query parameter versioning (e.g., /users?v=1), header versioning, and content negotiation.

Ques 19. What is the purpose of the '406 Not Acceptable' HTTP status code?

The '406 Not Acceptable' status code is returned when the server cannot produce a response matching the list of acceptable values defined in the 'Accept' header of the request.

Ques 20. Explain the concept of Bearer token authentication in Web APIs.

Bearer token authentication involves including a token (commonly a JWT) in the 'Authorization' header of the HTTP request. The server validates the token to authenticate the user and authorize the requested action.

Example:

Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c

Ques 21. What is the role of API documentation, and how does it contribute to the development process?

API documentation serves as a guide for developers on how to use and integrate with an API. It provides information on endpoints, request/response formats, authentication, and examples, making it crucial for developers to understand and implement the API correctly.

Ques 22. Explain the concept of idempotency in the context of Web API methods.

An idempotent operation produces the same result whether it is applied once or multiple times. In the context of Web APIs, HTTP methods like GET, PUT, and DELETE are expected to be idempotent, ensuring consistent behavior regardless of the number of requests.

Ques 23. Explain the purpose of the '204 No Content' HTTP status code.

The '204 No Content' status code indicates a successful request, but there is no additional information to send in the response payload. It is commonly used for operations where a response body is not necessary.

Ques 24. What is the purpose of the '429 Too Many Requests' HTTP status code?

The '429 Too Many Requests' status code indicates that the user has sent too many requests in a given amount of time. It is used to prevent abuse and ensure fair usage of the API.

Ques 25. Explain the role of content-type and accept headers in HTTP requests and responses.

The 'Content-Type' header in requests specifies the media type of the request payload, while the 'Accept' header in requests indicates the media types that are acceptable for the response. These headers play a crucial role in content negotiation between the client and server.

Ques 26. What is the purpose of the '401 Unauthorized' HTTP status code?

The '401 Unauthorized' status code indicates that the request has not been applied because it lacks valid authentication credentials. It is commonly used when a user needs to authenticate to access a protected resource.

Ques 27. What is JSON Web Token (JWT) and how is it used in Web APIs?

JWT is a compact, URL-safe means of representing claims to be transferred between two parties. In Web APIs, it is often used for authentication and information exchange.

Example:

Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c

Ques 28. What is the role of OAuth in Web API security?

OAuth is an open standard for access delegation commonly used in the context of user authentication and authorization. It allows third-party applications to access resources on behalf of a user without exposing their credentials.

Ques 29. What is HATEOAS, and how does it relate to RESTful Web APIs?

HATEOAS (Hypermedia As The Engine Of Application State) is a constraint in the REST architectural style where the response from a server provides links to related resources. It allows clients to navigate a web application dynamically.

Ques 30. Explain the concept of Hypermedia in the context of RESTful Web APIs.

Hypermedia refers to the inclusion of hyperlinks in a response, allowing clients to discover and navigate related resources. It is a key aspect of HATEOAS and enhances the flexibility and discoverability of RESTful APIs.

Ques 31. What are the advantages and disadvantages of using JSON Web Tokens (JWT) for authentication in Web APIs?

Advantages include statelessness, compactness, and ease of implementation. Disadvantages may include potential security risks if not properly implemented, and the inability to revoke tokens before expiration.