API-related interviews

In API-related interviews, questions typically cover different aspects of APIs, including REST, RESTful APIs, SOAP, GraphQL, authentication, security, performance, and best practices. Below is a categorized list of common API interview questions:

1. Basic API Questions

What is an API? Can you explain it in simple terms?
What is the difference between REST and RESTful API?
What are the key principles of REST architecture?
What is the difference between REST and SOAP?
What are the advantages and disadvantages of RESTful APIs?
What is the difference between REST and GraphQL?

2. HTTP Methods & CRUD Operations

What are the different HTTP methods used in RESTful APIs?
What is the difference between POST, PUT, and PATCH?
Why is GET considered an idempotent method?
Can you explain the difference between DELETE and PUT?

3. API Authentication & Security

What are the common methods of API authentication?
- Basic Authentication
- OAuth 2.0
- JWT (JSON Web Token)
- API Key authentication
What is OAuth 2.0? How does it work?
What is JWT, and how is it used for authentication?
How can you secure a REST API?
- Rate limiting
- Token-based authentication
- CORS (Cross-Origin Resource Sharing)
- HTTPS and TLS
What is API throttling?
What is CORS, and why is it important in APIs?

4. API Status Codes & Error Handling

What are HTTP status codes, and why are they important?
Can you explain some common HTTP status codes?
- 200 OK
- 201 Created
- 400 Bad Request
- 401 Unauthorized
- 403 Forbidden
- 404 Not Found
- 500 Internal Server Error
How should an API handle errors? (Best practices)

5. API Versioning & Documentation

Why is API versioning important?
What are the different ways to version a REST API?
- URI versioning (/v1/users)
- Query parameter versioning (/users?version=1)
- Header versioning (Accept: application/vnd.company.v1+json)
What is API documentation, and why is it important?
What tools can be used to document an API? (Swagger, Postman, OpenAPI)

6. API Performance & Optimization

How do you optimize a REST API for better performance?
- Caching (Redis, CDN, HTTP caching)
- Pagination
- Load balancing
- Database indexing
- Query optimization
What is pagination, and why is it used in APIs?
How does caching work in REST APIs?
What are WebSockets, and how do they differ from REST APIs?

7. Practical API Design & Testing

What are best practices for designing RESTful APIs?
What is HATEOAS in REST API?
How do you test an API?
- Postman
- JMeter (for load testing)
- Unit testing (JUnit, Jest, Mocha)
How do you handle long-running API requests? (Async processing, Webhooks)