TECH
REST Interview Questions and Answers: What works, red flags to watch, and more
REST APIs form the backbone of modern applications, with 83% adoption across industries.
Effective API developers understand not just HTTP methods but architectural principles like statelessness and HATEOAS.
Real-world challenges like authentication, versioning, error handling, and scalability differentiate strong candidates.
Scenario-based questions reveal practical problem-solving and production readiness.
Red flags such as lack of security awareness and poor communication can signal risky hires.
REST interview questions typically cover HTTP methods, status codes, and stateless design principles. Candidates explain CRUD operations and resource naming conventions perfectly.
But building production APIs involves challenges that theory doesn't address. When your API needs to handle rate limiting, authentication flows, or data consistency across microservices, knowing REST principles isn't enough. You need developers who understand how to build APIs that remain stable under real-world usage patterns.
We researched several articles on the internet, but all give you just a laundry list of 50-100 questions to ask, which doesn’t really help evaluate and predict the job performance of the candidate.
So in our guide, we also cover other important aspects to identify strong candidates fast –
key fundamental questions,
real-word scenario questions,
questions that reveal practical experience,
beyond technical questions
red flags to watch out for,
making the final decision
etc.
This guide helps engineering leaders ask the right REST interview questions to identify developers who can actually build robust APIs, not just recite textbook definitions.
Why REST API Skills Matter in 2025
Modern applications are built on APIs. RESTful APIs have become the backbone of modern web application architectures, providing a flexible and scalable way of integrating different systems and services.
Yet most technical interviews fail to distinguish between developers who understand REST concepts and those who can implement them effectively.
The challenge isn't finding candidates who know what GET and POST do. It's identifying developers who can design APIs that handle real-world complexity like authentication failures, rate limiting, and data consistency.
Traditional resume screening misses this entirely. A candidate might list "REST API development" but struggle with basic error handling or security implementation. The cost of a bad hire in API development extends beyond salary - poor API design creates technical debt that impacts your entire system architecture.
Key Statistics:
83% of APIs use REST architecture
Average time to identify a bad technical hire: 3-6 months
Cost of replacing a mis-hired developer: 150-300% of annual salary
API Usage in Modern Applications
Application Type | API Dependency Level | Common Use Cases |
Mobile Apps | Critical (90%+) | User authentication, data sync, push notifications |
Web Applications | High (70-80%) | Database operations, third-party integrations |
Microservices | Essential (100%) | Inter-service communication, data exchange |
IoT Systems | High (80%+) | Device management, telemetry data collection |
Did you know? While PUT is idempotent (safe to repeat), PATCH methods' idempotency depends on how they are implemented—an often overlooked subtlety in REST API design.
Boost your hiring precision with Utkrusht — the AI-driven platform designed to accurately assess REST API expertise. Pinpoint candidates who can build scalable, secure, and efficient APIs that power your business. Join Utkrusht today and elevate your developer recruitment process.
Essential REST Fundamentals Questions for Freshers
Explain the difference between PUT and PATCH methods
What you're testing: Understanding of HTTP semantics and idempotency.
Strong answer: PUT replaces the entire resource and is idempotent. PATCH updates specific fields and may or may not be idempotent depending on implementation. A good candidate will mention when to use each method.
Red flag answer: "PUT is for updates, PATCH is for partial updates" without explaining idempotency or implementation considerations.
What makes an API RESTful?
What you're testing: Grasp of REST architectural constraints.
Strong answer: Stateless communication, uniform interface, client-server architecture, cacheable responses, layered system. Bonus points for mentioning HATEOAS even if they note it's rarely implemented.
Red flag answer: Only mentioning HTTP methods or JSON responses without understanding the underlying principles.
How do you handle errors in REST APIs?
What you're testing: Practical experience with error scenarios.
Strong answer: Proper HTTP status codes, consistent error response format, meaningful error messages, logging for debugging. Should mention different error types (4xx vs 5xx).
Red flag answer: "Return 200 OK with error details in the response body" or only mentioning status codes without explaining error response structure.
HTTP Methods Comparison
Method | Purpose | Idempotent | Safe | Common Use Case |
GET | Retrieve data | ✓ | ✓ | Fetch user profile |
POST | Create resource | ✗ | ✗ | Create new user |
PUT | Replace resource | ✓ | ✗ | Update entire user record |
PATCH | Partial update | Maybe | ✗ | Update user email only |
DELETE | Remove resource | ✓ | ✗ | Delete user account |
Intermediate REST API Questions
How would you implement API authentication for a mobile app?
What you're testing: Security understanding and practical implementation experience.
Strong answer: JWT tokens with refresh mechanism, secure token storage, proper token expiration, consideration of device-specific challenges. Should mention HTTPS requirement and token revocation strategies.
Red flag answer: Basic authentication over HTTP, storing passwords in tokens, or no mention of token refresh mechanisms.
Describe your approach to API versioning.
What you're testing: Experience with API evolution and backward compatibility.
Strong answer: Clear versioning strategy (URL path, headers, or accept headers), deprecation timeline, migration support, documentation updates. Should discuss trade-offs of different approaches.
Red flag answer: "Just increment the version number" without considering client migration or backward compatibility impact.
How do you ensure your APIs can handle high traffic?
What you're testing: Scalability awareness and performance optimization knowledge.
Strong answer: Caching strategies, rate limiting, database optimization, load balancing, monitoring. Should mention specific bottlenecks and mitigation strategies.
Red flag answer: Generic answers about "making it faster" without specific techniques or understanding of performance bottlenecks.
Authentication Flow Diagram
Client Request → API Gateway → Authentication Service → Resource Server
↓ ↓ ↓ ↓
Include JWT → Validate Token → Generate/Refresh → Return Data
↓ ↓ ↓ ↓
Store Token ← Return Response ← Log Activity ← Process Request
Advanced REST Implementation Questions & Real-World Scenario Questions
Design an API for a social media platform's news feed. Walk me through your approach.
What you're testing: System design skills, understanding of complex API requirements.
Strong answer: Pagination strategy, caching layers, real-time updates, content filtering, performance optimization. Should discuss data modeling, security, and scalability challenges.
Red flag answer: Simple CRUD operations without considering feed complexity, real-time requirements, or scale challenges.
How would you handle eventual consistency in a distributed API system?
What you're testing: Understanding of distributed systems and data consistency models.
Strong answer: Event-driven architecture, saga patterns, compensation logic, monitoring inconsistencies. Should discuss trade-offs between consistency and availability.
Red flag answer: Avoiding the question or suggesting synchronous solutions that don't scale.
Describe your strategy for API monitoring and observability.
What you're testing: Production readiness and operational awareness.
Strong answer: Metrics collection, distributed tracing, error tracking, performance monitoring, alerting strategies. Should mention specific tools and implementation approaches.
Red flag answer: Basic logging without understanding of comprehensive monitoring or production debugging strategies.
API Architecture Diagram
Load Balancer
↓
API Gateway (Rate Limiting, Auth, Monitoring)
↓
┌─────────────────────────────────────┐
│ Microservices Layer │
│ ┌─────┐ ┌─────┐ ┌─────┐ ┌─────┐ │
│ │Users│ │Posts│ │Media│ │Notif│ │
│ └─────┘ └─────┘ └─────┘ └─────┘ │
└─────────────────────────────────────┘
↓
┌─────────────────────────────────────┐
│ Data Layer │
│ ┌─────┐ ┌─────┐ ┌─────┐ ┌─────┐ │
│ │ DB │ │Cache│ │Queue│ │Store│ │
│ └─────┘ └─────┘ └─────┘ └─────┘ │
└─────────────────────────────────────┘
A client reports that API responses are inconsistent. Sometimes they get user data, sometimes they don't, for the same request. How do you troubleshoot this?
What you're testing: Debugging methodology and systematic problem-solving.
Strong answer: Check caching layers, database replication lag, load balancer configuration, race conditions. Should outline a systematic debugging approach with specific tools and techniques.
Red flag answer: Guessing at solutions without a methodical troubleshooting approach or understanding of common consistency issues.
Your API suddenly starts returning 500 errors for 20% of requests. Walk me through your response.
What you're testing: Incident response skills and production debugging experience.
Strong answer: Immediate monitoring check, error log analysis, rollback consideration, client communication, root cause analysis process. Should demonstrate urgency while maintaining systematic approach.
Red flag answer: Panic response or suggesting to "restart everything" without investigation.
Design rate limiting for an API that serves both web and mobile clients with different usage patterns.
What you're testing: Understanding of different client needs and flexible system design.
Strong answer: Different rate limits per client type, sliding window algorithms, graceful degradation, client feedback mechanisms. Should consider business requirements and user experience.
Red flag answer: One-size-fits-all approach without considering different client characteristics or usage patterns.
Problem-Solving Flowchart
API Issue Reported
↓
Check Monitoring Dashboard
↓
Identify Error Pattern
↙ ↘
Client Error Server Error
(4xx codes) (5xx codes)
↓ ↓
Review Request Check Server
Format Logs
↓ ↓
Document Fix Apply Hot Fix
↓ ↓
Update Docs Root Cause
Analysis
Questions That Reveal Practical Experience
Describe a challenging API integration you've worked on. What made it difficult?
What you're testing: Real-world experience and problem-solving approach.
Strong answer: Specific technical challenges, solution approach, lessons learned. Should demonstrate understanding of integration complexity beyond basic HTTP requests.
Red flag answer: Generic or theoretical problems without specific details or learnings.
How do you test REST APIs? Walk me through your testing strategy.
What you're testing: Quality assurance approach and testing experience.
Strong answer: Unit tests, integration tests, contract tests, performance tests. Should mention specific tools and testing scenarios including edge cases.
Red flag answer: Only mentioning manual testing or basic unit tests without comprehensive testing strategy
Tell me about a time when you had to optimize API performance. What was your approach?
What you're testing: Performance optimization experience and analytical thinking.
Strong answer: Performance measurement, bottleneck identification, specific optimization techniques, results measurement. Should demonstrate data-driven approach.
Red flag answer: Generic performance tips without specific experience or measurement approaches.
Testing Pyramid for APIs
┌─────────────┐
│ E2E Testing │ (10%)
│ Manual │
└─────────────┘
┌─────────────────┐
│ Integration │ (20%)
│ Testing │
│ (API Contracts) │
└─────────────────┘
┌───────────────────────┐
│ Unit Testing │ (70%)
│ (Business Logic) │
│ Fast & Isolated │
└───────────────────────┘
Red Flags to Watch For
Recognize these warning signs that indicate a candidate may not have genuine REST API experience.
Theoretical Knowledge Only:
Perfect textbook answers without practical context
Unable to explain trade-offs or real-world challenges
No mention of debugging or troubleshooting experience
Security Blind Spots:
Suggesting HTTP for sensitive data
No mention of input validation or authentication
Treating security as an afterthought
Scalability Unawareness:
No consideration of performance implications
Designing APIs that won't scale beyond toy applications
No understanding of caching or optimization strategies
Poor Communication:
Can't explain technical concepts in simple terms
Defensive about technical choices
Unable to discuss trade-offs or alternative approaches
Warning Signs Checklist
Red Flag Category | Warning Signs | Impact Level |
Security | No HTTPS mention, basic auth over HTTP | 🔴 Critical |
Design | RPC-style endpoints, inconsistent naming | 🟡 Medium |
Error Handling | Generic responses, no status codes | 🟠 High |
Performance | No caching strategy, N+1 query patterns | 🟠 High |
Testing | Manual testing only, no automation | 🟡 Medium |
Beyond Technical Questions
Technical competency alone doesn't guarantee success. Evaluate these broader skills that impact team effectiveness and project outcomes.
Communication Assessment:
Can they explain complex technical concepts to non-technical stakeholders?
Do they ask clarifying questions about requirements?
How do they handle disagreement about technical approaches?
Problem-Solving Approach:
Do they break down complex problems systematically?
Are they comfortable with ambiguous requirements?
Can they identify and articulate assumptions?
Collaboration Skills:
How do they approach code reviews and feedback?
Do they consider the impact of their work on other team members?
Can they work effectively with front-end developers and product managers?
Learning Mindset:
How do they stay current with API best practices?
Are they open to new approaches and technologies?
Do they learn from mistakes and adapt their approach?
Skills Assessment Matrix
Skill Category | Beginner | Intermediate | Advanced | Expert |
REST Fundamentals | Basic HTTP methods | Status codes, headers | HATEOAS, Richardson model | Architectural patterns |
Security | Basic auth concepts | JWT implementation | OAuth flows, RBAC | Zero-trust architecture |
Performance | Basic caching | Database optimization | CDN strategies | Microservices optimization |
Design | CRUD operations | Resource modeling | API versioning | Event-driven design |
Making the Final Decision
Combine interview insights with practical assessments to build a complete picture of candidate ability.
Scoring Framework:
Technical competency (40%): Core REST knowledge and implementation skills
Problem-solving (30%): Approach to debugging and system design
Communication (20%): Ability to explain concepts and collaborate
Experience relevance (10%): Specific background matching your needs
Key Decision Factors:
Can they handle the complexity of your current API challenges?
Will they contribute to better API design practices on your team?
Do they demonstrate growth potential for future challenges?
How quickly can they become productive in your environment?
When to Move Forward:
Strong technical fundamentals with practical experience
Clear communication and collaborative approach
Demonstrates learning mindset and adaptability
Shows understanding of real-world API challenges
When to Pass:
Theoretical knowledge without practical application
Poor communication or defensive about technical choices
No awareness of security or performance implications
Cannot explain past work or learning experiences
The goal isn't finding perfect candidates - it's identifying developers who can solve your specific API challenges and grow with your team.
Don’t leave your API hiring to chance. Utkrusht’s intelligent skill assessments go beyond buzzwords to validate real-world REST capabilities. Empower your tech team with top talent by signing up with Utkrusht — smart hiring for modern API challenges.
Want to hire
the best talent
with proof
of skill?
Shortlist candidates with
strong proof of skill
in just 48 hours
Co-founder, Utkrusht AI
