Web API Interview Questions And Answers
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Best Web API Interview Questions and Answers
Preparing for a Web API interview requires a solid understanding of RESTful services, HTTP methods, API security, authentication, status codes, JSON/XML data formats, versioning, error handling, and API testing. Whether you’re a fresher looking to start a career in web development or an experienced professional aiming for a backend or full-stack developer role, interviewers often assess both your theoretical knowledge and practical experience with Web APIs. To help you succeed, CourseJet has compiled this comprehensive list of the Top 50 Web API Interview Questions and Answers, covering everything from fundamental concepts to advanced topics commonly asked in technical interviews. These carefully selected questions with detailed answers will help you strengthen your knowledge, improve your confidence, and perform well in your next Web API interview.
A Web API (Application Programming Interface) is a set of rules and protocols that allows different software applications to communicate over the web using HTTP. It enables clients to access server-side resources and services.
REST (Representational State Transfer) is an architectural style for designing web services that are stateless, scalable, and use standard HTTP methods such as GET, POST, PUT, PATCH, and DELETE.
A Web API is a broader concept that can use HTTP and various formats like JSON and XML. A Web Service typically uses SOAP, XML, and strict communication protocols.
- Platform independent
- Lightweight communication
- Easy integration
- Supports multiple data formats
- Scalable and secure
- Enables mobile and web applications
- GET – Retrieve data
- POST – Create data
- PUT – Update an entire resource
- PATCH – Partially update a resource
- DELETE – Remove a resource
An endpoint is a specific URL where an API can be accessed to perform operations on a resource.
JSON (JavaScript Object Notation) is a lightweight, human-readable data format commonly used for exchanging data between clients and servers.
XML (eXtensible Markup Language) is a markup language used to store and transport structured data.
Statelessness means each client request contains all the information required to process it. The server does not store client session information between requests.
- Client-Server
- Stateless
- Cacheable
- Uniform Interface
- Layered System
- Code on Demand (optional)
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PUT updates the entire resource, while PATCH updates only the specified fields.
HTTP status codes indicate the result of an HTTP request, such as success, client errors, or server errors.
- 200 OK
- 201 Created
- 204 No Content
- 400 Bad Request
- 401 Unauthorized
- 403 Forbidden
- 404 Not Found
- 409 Conflict
- 500 Internal Server Error
API versioning allows developers to introduce changes without breaking existing client applications.
- URI Versioning
- Query Parameter Versioning
- Header Versioning
- Media Type Versioning
An idempotent operation produces the same result regardless of how many times it is executed.
GET, PUT, DELETE, HEAD, OPTIONS, and TRACE are idempotent methods.
Authentication verifies the identity of a user or application before granting access.
Authorization determines what an authenticated user is allowed to access or perform.
It is a pattern that minimizes the risk of bringing up new version software into the existing production environment. It can be achieved by introducing canary release to the subset of users before introducing it to the complete users available in a controlled manner.
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JWT (JSON Web Token) is a compact token format used to securely transmit user information between parties.
OAuth 2.0 is an authorization framework that allows third-party applications to access resources on behalf of users.
Cross-Origin Resource Sharing (CORS) is a browser security feature that controls access to resources from different origins.
An API Gateway acts as a single entry point for client requests and provides routing, authentication, rate limiting, and monitoring.
Rate limiting restricts the number of API requests a client can make within a specific time period.
API throttling temporarily limits client requests to prevent server overload.
API documentation describes endpoints, request parameters, authentication, response formats, and usage examples.
Swagger is a set of tools for designing, documenting, and testing REST APIs using the OpenAPI Specification.
OpenAPI Specification (OAS) is a standard format for describing RESTful APIs.
Content negotiation allows clients and servers to agree on response formats such as JSON or XML.
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Request headers provide metadata such as authentication, content type, language, and caching preferences.
Response headers provide additional information about the server response, caching, content type, and security.
The Accept header specifies the response media type preferred by the client.
The Content-Type header indicates the format of the request or response body.
Serialization converts objects into formats like JSON or XML for transmission or storage.
Deserialization converts JSON or XML back into application objects.
Pagination divides large datasets into smaller pages to improve performance and usability.
Filtering allows clients to retrieve only data matching specified criteria.
Sorting arranges returned data in ascending or descending order based on one or more fields.
Caching stores API responses temporarily to reduce server load and improve response times.
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- JSON
- XML
- YAML
- Plain Text
- HTML (less common)
HATEOAS (Hypermedia as the Engine of Application State) is a REST principle where responses include links to related resources and available actions.
API testing verifies the functionality, reliability, security, and performance of an API without relying on a user interface.
- Postman
- Swagger UI
- SoapUI
- Insomnia
- cURL
- JMeter
An API mock simulates API behavior, allowing frontend and backend teams to develop and test independently.
Webhooks are HTTP callbacks that send real-time notifications to another application when specific events occur.
Synchronous APIs require the client to wait for a response, while asynchronous APIs allow processing to continue and notify the client when the operation is complete.
- Use HTTPS
- Implement authentication and authorization
- Validate user input
- Enable rate limiting
- Encrypt sensitive data
- Log and monitor API activity
- Prevent SQL injection and XSS attacks
- Use meaningful resource names
- Follow HTTP standards
- Return appropriate status codes
- Implement versioning
- Provide clear error messages
- Secure endpoints
- Document APIs thoroughly
- Use pagination and filtering for large datasets
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