18Software Engineering · Interview Prep · Free
.NET Developer interview questions — and how to answer them.
These are the questions .NET Developer candidates are most likely to face, from openers to the hard ones — each with a note on what a strong answer covers. Want more, tuned to your level? Use the free generator below.
What interviewers look for in a .NET Developer
- Concrete examples of systems you've built, with the trade-offs you weighed
- How you debug — the process, not just the fix
- Collaboration signals: code review, disagreements, mentoring
Likely .NET Developer interview questions
1. Tell us about your experience with C# and .NET. What versions have you worked with?
Mention specific versions (Framework, Core, .NET 5+), key features used, and years of hands-on experience.
2. Describe a time when you had to debug a complex issue in production. How did you approach it?
Show systematic debugging process, tools used (debugger, logging, profilers), and how you communicated the resolution.
3. What is the difference between abstract classes and interfaces in C#? When would you use each?
Explain inheritance vs. contracts, multiple inheritance considerations, and provide practical use-case examples.
4. Walk us through your experience with Entity Framework. Have you used EF Core vs. EF6?
Discuss ORM concepts, migrations, lazy/eager loading, query optimization, and specific migration challenges faced.
5. Tell me about a time you had to refactor legacy code. What was your approach and what challenges did you face?
Highlight planning, testing strategy, maintaining functionality, stakeholder communication, and measurable improvements.
6. How do you handle dependency injection in .NET? Explain the built-in DI container vs. third-party alternatives.
Cover service lifetimes (transient/scoped/singleton), constructor injection, configuration, and when to use alternative containers.
7. Describe your experience building and consuming REST APIs. How do you handle versioning and error handling?
Discuss API design principles, status codes, versioning strategies (URL/header), consistent error responses, and documentation.
8. What's your approach to unit testing in .NET? Which frameworks and testing patterns do you prefer?
Mention xUnit/NUnit/MSTest, mocking frameworks (Moq), AAA pattern, test coverage goals, and real examples of difficult-to-test scenarios.
9. Explain async/await in C# and common pitfalls you've encountered. How do you avoid deadlocks?
Cover Task-based asynchrony, ConfigureAwait(false), async all the way down principle, common mistakes, and synchronization context.
10. How do you approach security in .NET applications? Discuss authentication, authorization, and data protection.
Address OAuth/OpenID Connect, role-based/claims-based authorization, encryption at rest/transit, OWASP vulnerabilities, and input validation.
11. Describe your experience with cloud platforms (.NET on Azure, AWS). How have you optimized for cloud deployment?
Mention specific services (App Service, Functions, Container Registry), scalability considerations, cost optimization, and monitoring strategies.
12. Design a high-performance .NET system that must handle 10K+ concurrent requests. Walk through your architectural decisions.
Cover caching strategies, database optimization, async patterns, load balancing, monitoring, database connection pooling, and trade-offs considered.
Want to practice answering live with scored feedback? Try the Mock Interview Coach. Applying too? See a .NET Developer cover letter example.
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