REST API Interview Questions: Top 50 Questions & Answers 2025 Guide

REST API interviews have become increasingly crucial in today's tech landscape, with developers spending an average of 30% of their time coding APIs, according to recent industry statistics. As nearly 90% of developers are using APIs in some capacity, mastering REST API interview questions is essential for career advancement in software development.

Whether you're a junior developer preparing for your first API-focused role or a senior engineer looking to level up, this comprehensive guide covers the most important REST API Interview Questions professionals encounter, backed by expert insights and real-world statistics.

Understanding the REST API Interview Landscape

Q: Why are REST API questions so prevalent in technical interviews? 

A: REST APIs dominate the modern development ecosystem with a 70% adoption rate, showcasing their monumental impact on the digital world. Their simplicity, scalability, and versatility make them indispensable for businesses streamlining operations across platforms and languages.

Q: What percentage of developer interviews include REST API questions? 

A: Based on industry surveys and hiring manager feedback, approximately 85% of backend developer interviews and 70% of full-stack developer interviews include REST API-related questions, reflecting their critical importance in modern software architecture.

Fundamental REST API Interview Questions (Questions 1-15)

Core Concepts and Definitions

Q1: What is REST, and how does it differ from other architectural styles? 

A: REST (Representational State Transfer) is an architectural style for designing networked applications, not a protocol or standard. Unlike SOAP, which is protocol-based, REST leverages existing HTTP methods and is stateless, making it more lightweight and scalable.

Key REST Principles:

1. Stateless: Each request contains all the information needed to process it

2. Client-Server Architecture: Clear separation of concerns

3. Cacheable: Responses can be cached to improve performance

4. Uniform Interface: A Consistent way of interacting with resources

5. Layered System: Architecture can be composed of hierarchical layers

6. Code on Demand: Optional constraint allowing executable code transfer

Q2: What are the main HTTP methods used in REST APIs? 

A: The primary HTTP methods include:

• GET: Retrieve data from a server

• POST: Create new resources

• PUT: Update existing resources (full replacement)

• PATCH: Partial updates to resources

• DELETE: Remove resources

• HEAD: Retrieve headers without response body

• OPTIONS: Get allowed methods for a resource

Q3: What is the difference between PUT and PATCH methods? 

A: PUT replaces the entire resource with the provided data (idempotent), while PATCH applies partial modifications to a resource. PUT requires sending the complete resource representation, whereas PATCH only sends the fields that need to be updated.

Q4: What is idempotency in REST APIs? 

A: Idempotency means that multiple identical requests should have the same effect as a single request. GET, PUT, DELETE, HEAD, and OPTIONS are idempotent, while POST and PATCH are not necessarily idempotent.

Q5: What is a resource in REST? 

A: A resource is any information that can be named and addressed via a URI. Resources represent entities like users, products, or orders, and are manipulated using standard HTTP methods.

Q6: What is the difference between REST and RESTful? 

A: REST is the architectural style itself, while RESTful describes web services that adhere to REST principles. A RESTful API follows REST constraints and uses HTTP methods appropriately.

Q7: What is statelessness in REST? 

A: Statelessness means the server doesn't store any client context between requests. Each request must contain all information necessary to understand and process it, making the system more scalable and reliable.

Q8: What is HATEOAS? 

A: HATEOAS (Hypermedia as the Engine of Application State) is a REST constraint where responses include hypermedia links that guide clients on available actions and navigation paths.

Q9: What is content negotiation in REST APIs? 

A: Content negotiation allows clients and servers to agree on the best representation format (JSON, XML, HTML) using HTTP headers like Accept, Content-Type, and Accept-Language.

Q10: What is the difference between URI and URL? 

A: URI (Uniform Resource Identifier) is a string that identifies resources, while URL (Uniform Resource Locator) is a type of URI that specifies the location and access method for a resource.

Status Codes and Error Handling

Q11: What are the most important HTTP status codes for REST APIs? 

A: Critical status codes include:

Status Code	Meaning	Use Case
200	OK	Successful GET, PUT, PATCH
201	Created	Successful POST
204	No Content	Successful DELETE
400	Bad Request	Invalid client request
401	Unauthorized	Authentication required
403	Forbidden	Authorization failed
404	Not Found	Resource doesn't exist
409	Conflict	Resource conflict
500	Internal Server Error	Server error

Q12: What's the difference between 401 and 403 status codes? 

A: 401 (Unauthorized) means authentication is required or has failed, while 403 (Forbidden) means the server understood the request but refuses to authorize it due to insufficient permissions.

Q13: When should you use the 204 No Content status code? 

A: Use 204 when an operation is successful but there's no content to return, typically for DELETE operations or successful PUT/PATCH requests where you don't need to return the updated resource.

Q14: What are 2xx, 3xx, 4xx, and 5xx status code categories? 

A:

• 2xx (Success): Request was successful

• 3xx (Redirection): Further action needed to complete request

• 4xx (Client Error): Client-side error in the request

• 5xx (Server Error): Server-side error processing request

Q15: How do you handle validation errors in REST APIs? 

A: Return 400 Bad Request with detailed error messages in the response body, preferably in a structured format that includes field-specific validation errors and error codes.

Advanced REST API Interview Questions (Questions 16-35)

Security and Authentication

Q16: How do you implement authentication in REST APIs? 

A: Common authentication methods include:

1. API Keys: Simple but less secure for sensitive data

2. JWT (JSON Web Tokens): Stateless, self-contained tokens

3. OAuth 2.0: Industry standard for authorization

4. Basic Authentication: Username/password encoded in base64

5. Bearer Tokens: Token-based authentication

Expert Insight: Security remains a top concern, with 67% of organizations citing API security as their primary challenge in 2024, according to recent industry surveys.

Q17: What is JWT, and how does it work? 

A: JWT (JSON Web Token) is a compact, URL-safe token format for securely transmitting information. It consists of three parts: header (algorithm info), payload (claims), and signature (verification). JWTs are stateless and can contain user information and permissions.

Q18: What are the advantages and disadvantages of JWT? 

A: Advantages: Stateless, self-contained, cross-domain compatible, scalable Disadvantages: Cannot be revoked easily, token size can be large, potential security risks if not implemented properly

Q19: What is OAuth 2.0, and its flow types? 

A: OAuth 2.0 is an authorization framework. Main flows include:

• Authorization Code: Most secure, used for server-side apps

• Implicit: For client-side apps (deprecated)

• Resource Owner Password: For trusted applications

• Client Credentials: For machine-to-machine communication

Q20: How do you implement rate limiting in REST APIs? 

A: Rate-limiting strategies include:

• Token Bucket: Allows bursts of requests

• Fixed Window: Limits requests per time window

• Sliding Window: More flexible time-based limiting

• Sliding Window Log: Tracks individual request timestamps

Q21: What is CORS, and hhow do you handle it? 

A: CORS (Cross-Origin Resource Sharing) is a mechanism that allows restricted resources to be requested from another domain. Handle it by setting appropriate headers like Access-Control-Allow-Origin, Access-Control-Allow-Methods, and Access-Control-Allow-Headers.

Q22: How do you secure REST APIs against common attacks? 

A: Security measures include:

• Input validation and sanitization

• SQL injection prevention

• HTTPS enforcement

• Authentication and authorization

• Rate limiting

• OWASP security guidelines compliance

Performance and Optimization

Q23: What strategies do you use to optimize REST API performance? 

A: Key optimization techniques include:

• Caching: Implement HTTP caching headers (Cache-Control, ETag)

• Pagination: Limit response size for large datasets

• Rate Limiting: Prevent API abuse and ensure fair usage

• Compression: Use GZIP compression for responses

• Database Optimization: Efficient queries and indexing

• CDN Implementation: Distribute content globally

Q24: How do you handle API versioning? 

A: Common versioning strategies:

1. URL Versioning: /api/v1/users

2. Header Versioning: Accept: application/vnd.api+json;version=1

3. Query Parameter: /api/users?version=1

4. Content Negotiation:  Using Accept headers

Q25: What is pagination, and how do you implement it? 

A: Pagination divides large datasets into smaller chunks. Implementation methods:

• Offset-based: ?offset=20&limit=10

• Cursor-based: ?cursor=xyz&limit=10

• Page-based: ?page=3&size=10

Q26: What is caching in REST APIs, and its types? 

A: Caching stores frequently accessed data to reduce server load and improve response times. Types include:

• Browser caching: Client-side caching

• Proxy caching: Intermediate server caching

• Server caching: Application-level caching

• Database caching: Query result caching

Q27: How do you implement ETags for caching? 

A: ETags are HTTP headers that represent resource versions. The server generates an ETag for resources, client includes the If-None-Match header in subsequent requests. Server returns 304 Not Modified if ETag matches, otherwise returns updated resource with new ETag.

Q28: What is compression in REST APIs? 

A: Compression reduces response size using algorithms like GZIP. Enable by setting Accept-Encoding: gzip in requests and Content-Encoding: gzip in responses. Can reduce bandwidth usage by 60-80%.

Q29: How do you handle large payloads in REST APIs? 

A: Strategies include:

• Streaming: Process data in chunks

• Pagination: Break large results into pages

• Compression: Reduce payload size

• Async processing: Handle requests asynchronously

• File uploads: Use multipart/form-data

Q30: What is Connection Pooling? 

A: Connection pooling reuses database connections instead of creating new ones for each request. Improves performance by reducing connection overhead and limiting concurrent connections.

Error Handling and Logging

Q31: How do you design error responses in REST APIs? 

A: Best practices for error responses:

{
  "error": {
    "code": "VALIDATION_ERROR",
    "message": "Invalid input data",
    "details": [
      {
        "field": "email",
        "message": "Invalid email format"
      }
    ]
  }
}

Q32: What is the difference between client errors and server errors? 

A: Client errors (4xx) indicate problems with the request (invalid data, authentication issues), while server errors (5xx) indicate problems on the server side (database issues, internal errors).

Q33: How do you implement logging in REST APIs? 

A: Logging best practices:

• Log all requests and responses

• Include correlation IDs for tracing

• Log error details and stack traces

• Use structured logging (JSON format)

• Implement different log levels (DEBUG, INFO, WARN, ERROR)

Q34: What is a circuit breaker pattern? 

A: Circuit breaker prevents cascading failures by monitoring service calls. States include:

• Closed: Normal operation

• Open: Failing fast without calling the service

• Half-Open: Testing if the service recovered

Q35: How do you handle timeouts in REST APIs? 

A: Timeout strategies include:

• Connection timeout: Time to establish a connection

• Request timeout: Maximum request processing time

• Retry mechanisms: Exponential backoff

• Graceful degradation: Fallback responses

Testing and Documentation Interview Questions (Questions 36-50)

API Testing Approaches

Q36: What types of testing are important for REST APIs? 

A: Essential testing types include:

• Unit Testing: Individual endpoint functionality

• Integration Testing: API interactions with databases/services

• Contract Testing: API adherence to specifications

• Performance Testing: Load, stress, and scalability testing

• Security Testing: Vulnerability assessments

• End-to-End Testing: Complete user workflow validation

Q37: What tools do you use for API testing? 

A: Popular testing tools include:

• Postman: Manual and automated API testing

• Insomnia: REST client for API design and testing

• Jest/Mocha: JavaScript testing frameworks

• Pytest: Python testing framework

• Newman: Command-line collection runner for Postman

• Apache JMeter: Performance testing tool

Q38: How do you write unit tests for REST APIs? 

A: Unit testing approaches:

• Test individual endpoints in isolation

• Mock external dependencies

• Test various input scenarios (valid, invalid, edge cases)

• Verify response status codes and content

• Test error handling scenarios

Q39: What is contract testing, and why is it important? 

A: Contract testing ensures APIs adhere to agreed-upon specifications between providers and consumers. It prevents breaking changes and maintains API compatibility across different services.

Q40: How do you perform load testing for REST APIs? 

A: Load testing strategies:

• Define realistic user scenarios

• Gradually increase concurrent users

• Monitor response times and error rates

• Test database performance under load

• Identify bottlenecks and scalability limits

Q41: What is API mocking, and when do you use it? 

A: API mocking creates fake API responses for testing purposes. Use cases include:

• Testing frontend applications before backend completion

• Isolating components during testing

• Simulating error scenarios

• Development environment setup

Documentation Best Practices

Q42: How do you document REST APIs effectively? 

A: Best practices for API documentation:

1. OpenAPI/Swagger Specifications: Industry-standard API documentation

2. Interactive Documentation: Allow testing directly from the docs

3. Code Examples: Provide samples in multiple programming languages

4. Error Documentation: Comprehensive error codes and messages

5. Authentication Guides: Clear authentication implementation steps

6. Rate Limiting Information: Usage limits and guidelines

Q43: What is the OpenAPI specification? 

A: OpenAPI (formerly Swagger) is a specification for describing REST APIs. It defines endpoints, request/response schemas, authentication methods, and other API details in a standardized format.

Q44: How do you maintain API documentation? 

A: Documentation maintenance strategies:

• Auto-generate documentation from code annotations

• Keep documentation in version control

• Update documentation with each API change

• Review documentation during code reviews

• Use tools like Swagger/OpenAPI for consistency

Q45: What should be included in API documentation? 

A: Essential documentation elements:

• Endpoint descriptions and usage

• Request/response examples

• Authentication requirements

• Error codes and messages

• Rate limiting information

• SDK and code samples

• Getting started guide

Advanced Topics

Q46: What is GraphQL, and how does it compare to REST? 

A: GraphQL is a query language that allows clients to request specific data. Compared to REST:

• GraphQL: Single endpoint, client-specified queries, strongly typed

• REST: Multiple endpoints, server-defined responses, HTTP methods

Q47: What are webhooks, and how do they differ from REST APIs? 

A: Webhooks are HTTP callbacks that notify applications of events. Unlike REST APIs, where clients request data, webhooks push data to clients when events occur.

Q48: How do you implement file uploads in REST APIs? 

A: File upload methods:

• Multipart/form-data: Standard approach for file uploads

• Base64 encoding: Embed files in JSON (limited by size)

• Presigned URLs: Direct upload to cloud storage

• Chunked upload: Break large files into pieces

Q49: What is an API gateway, and its benefits? 

A: API Gateway is a server that acts as an entry point for microservices. Benefits include:

• Request routing and load balancing

• Authentication and authorization

• Rate limiting and throttling

• Request/response transformation

• Monitoring and analytics

Q50: How do you handle partial updates in REST APIs? 

A: Partial update strategies:

• PATCH method: Send only changed fields

• Merge patch: Simple field replacement

• JSON Patch: Structured operations (add, remove, replace)

• Field selection: Allow clients to specify update fields

Bonus Questions (51-55)

Q51: What is eventual consistency in distributed systems? 

A: Eventual consistency means that, given enough time, all nodes in a distributed system will converge to the same state, even though they may be temporarily inconsistent.

Q52: How do you implement soft deletes in REST APIs? 

A: Soft deletes mark records as deleted without removing them physically. Implement by adding a deleted_at timestamp field and filtering out deleted records in queries.

Q53: What is the Richardson Maturity Model? 

A: A model that classifies REST APIs into four levels:

• Level 0: HTTP as transport

• Level 1: Resources

• Level 2: HTTP Verbs

• Level 3: Hypermedia Controls (HATEOAS)

Q54: How do you handle database transactions in REST APIs? 

A: Transaction handling strategies:

• Keep transactions short and focused

• Use database connection pooling

• Implement retry mechanisms for failures

• Consider eventual consistency for distributed systems

Q55: What is the API versioning strategy for breaking changes? 

A: Breaking change strategies:

• Maintain multiple API versions simultaneously

• Provide migration guides and deprecation notices

• Use semantic versioning (major.minor.patch)

• Implement gradual rollout and monitoring

Modern REST API Trends and Technologies

Emerging Patterns in 2025

Q: What are the current trends affecting REST API development? 

A: Key trends shaping REST APIs in 2025:

• AI-Powered APIs: The rise of AI-powered APIs that can provide more intelligent responses based on user data

• Serverless Architecture: The rise of serverless architecture, increased focus on API management, and treating APIs as standalone products

• GraphQL Competition: Just over 61% of respondents report the use of GraphQL in production, and an additional 10% report a replacement of REST with GraphQL

• API-First Development: Designing APIs before implementing applications

• Microservices Integration: APIs as the backbone of microservices architecture

Developer Tools and Workflows

Q: What development tools are essential for REST API development? 

A: Critical tools in the modern API development stack:

• API Design: Swagger Editor, Insomnia Designer

• Development: Postman, Thunder Client (VS Code)

• Testing: Newman, Dredd, Karate

• Monitoring: New Relic, Datadog, APItoolkit

• Security: OWASP ZAP, Snyk, Checkmarx

• Documentation: Swagger UI, Redoc, GitBook

Common Interview Scenarios and Problem-Solving

Real-World Problem Questions

Q: How would you design a REST API for a social media platform? 

A: Key considerations for social media API design:

1. Resource Identification:

   • /users/{id} - User profiles

   • /posts/{id} - Individual posts

   • /users/{id}/posts - User's posts

   • /posts/{id}/comments - Post comments

2. Scalability Considerations:

   • Implement pagination for feeds.

   • Use caching for frequently accessed data.

   • Consider rate limiting for posting actions.

   • Implement efficient search endpoints.

3. Security Measures:

   • OAuth 2.0 for user authentication

   • Privacy controls for user data

   • Content moderation endpoints

   • HTTPS enforcement

Q: How do you handle large file uploads in REST APIs? 

A: Strategies for file upload handling:

• Multipart Form Data: Standard approach for file uploads

• Chunked Upload: Break large files into smaller pieces

• Pre-signed URLs: Direct upload to cloud storage

• Streaming Upload: Real-time processing of upload data

• Progress Tracking: Provide upload status to clients

Industry Statistics and Market Insights

The REST API landscape continues to evolve rapidly:

• Market Dominance: REST reigns supreme as the top API architectural style

• Developer Adoption: Nearly 90% of developers are using APIs in some capacity

• Time Investment: Software developers spend an average of 30% of their time coding APIs

• Future Growth: The API economy is projected to reach $15 billion by 2025

Expert Quote: "Engineering managers who routinely assess candidates' proficiency with REST APIs" emphasize the importance of practical knowledge over theoretical understanding in interviews.

Conclusion

Mastering REST API interview questions requires a combination of theoretical knowledge and practical experience. With a 70% adoption rate of REST APIs and their continued dominance in the development landscape, thorough preparation in this area is essential for career success.

Focus on understanding core concepts, security best practices, performance optimization, and emerging trends. Practice with real-world scenarios and stay updated with the latest industry developments to excel in your REST API interviews.

Remember that interviewers value candidates who can demonstrate not just knowledge of REST principles, but also practical experience in implementing, testing, and maintaining robust API solutions.

Key Takeaways

• REST APIs dominate the market with a 70% adoption rate, making interview preparation crucial for developer success

• 30% of developer time is spent coding APIs, highlighting their central role in modern software development

• 90% of developers use APIs in some capacity, making REST API knowledge essential across all development roles

• Security and authentication are top interview topics, with JWT, OAuth 2.0, and API keys being most commonly discussed

• Performance optimization questions focus on caching, pagination, rate limiting, and database optimization strategies

• Testing knowledge is essential, covering unit, integration, performance, and security testing approaches

• Documentation skills using OpenAPI/Swagger specifications are highly valued by employers

• Modern trends include AI-powered APIs, serverless architecture, and API-first development approaches

• Problem-solving scenarios often involve designing APIs for real-world applications like social media or e-commerce platforms

• Tool proficiency in Postman, Swagger, testing frameworks, and monitoring solutions is expected in interviews

Improve your software testing flow with advanced API testing tools

Talk to us today

Frequently Asked Questions

Q: What's the difference between REST and RESTful APIs? 

A: REST is the architectural style, while RESTful refers to APIs that adhere to REST principles. A RESTful API follows REST constraints like statelessness, uniform interface, and proper use of HTTP methods.

Q: How many REST API interview questions should I prepare for? 

A: Most comprehensive interviews include 15-25 REST API questions covering fundamentals, security, testing, and practical scenarios. Prepare for both theoretical concepts and hands-on coding challenges.

Q: What's the most challenging REST API interview question? 

A: System design questions asking you to architect a complete API for complex applications (like designing Twitter's API) are typically the most challenging, requiring knowledge of scalability, security, and real-world constraints.

Q: Should I focus more on theory or practical examples? 

A: Balance both. While understanding REST principles is crucial, interviewers prefer candidates who can demonstrate practical implementation experience and problem-solving skills.

Q: How important is knowledge of API testing tools? 

A: Very important. Most companies expect familiarity with tools like Postman, Newman, or similar testing frameworks, as API testing is integral to the development process.

Q: What programming languages are most relevant for REST API interviews? 

A: While REST is language-agnostic, JavaScript/Node.js, Python, Java, and C# are most commonly used. Focus on the language relevant to the position you're applying for.

Q: How do I demonstrate REST API experience without a professional background? 

A: Build personal projects, contribute to open-source APIs, create comprehensive documentation, and showcase your work on GitHub with detailed README files and API documentation.

Article Sources

1. InterviewBit - Top REST API Interview Questions and Answers (2025)

2. HackerRank Blog - REST API Interview Questions to Know

3. Interview Zen - 6 REST API Interview Questions Every Hiring Manager Should Ask

4. Simplilearn - 40 REST API Interview Questions and Answers (2025)

5. Merge Dev - 10 Critical REST API Interview Questions for 2025

6. Turing - REST API Interview Q&A: Top 100 Picks

7. Indeed - 41 REST API Interview Questions (With Examples and Tips)

8. Nordic APIs - 20 Impressive API Economy Statistics

9. Analyzing Alpha - 23+ Amazing API Statistics for 2023

10. DreamFactory - 11 API Trends to Watch for in 2024