What C# Developers can expect at a technical interview

For C# developers aiming to secure new roles in 2025’s competitive jobs market, the technical interview is a crucial hurdle to overcome.

Interviewers for C# Developer jobs in 2025 tend to have a hybrid focus

Whether you're applying for a junior C# Development role as a freelance contractor or a full-time senior C# Developer position, technical tests help hiring managers assess your coding proficiency, problem-solving approach, and understanding of the C# ecosystem.

C# Development job interview: seven preparation areas

So, what exactly can you expect in a technical interview test as a C# developer?

Here’s a breakdown of the seven main areas of questions you might face and how to prepare for them effectively, writes Ben Quinn, head of technology recruitment at Leap29.

1. Coding Challenges: Testing Core C# Skills – four fundamental test areas

At the heart of almost every technical interview is a coding test. For C# developers, these challenges are typically designed to test four areas:

i) Syntax and language fundamentals: Expect to demonstrate your understanding of variables, loops, conditionals, data types, LINQ queries, exception handling, and collections.

ii) Object-Oriented Programming (OOP): C# is an object-oriented language, so you'll often be asked to write or refactor code involving classes, inheritance, interfaces, polymorphism, and encapsulation.

iii) Data Structures and Algorithms: You may be asked to solve problems involving arrays, lists, dictionaries, stacks, queues, trees, or graphs. Knowledge of sorting and searching algorithms, as well as time and space complexity (Big O notation), is often evaluated.

iv) Real-world scenarios: You might need to simulate a basic shopping cart, implement a logging system, or design a user registration flow.

If you’re a C# Development job candidate, be aware that these tests can be presented through platforms like Codility, HackerRank, or directly within an organisation’s in-house system.

2. System Design & Architecture (Mid to Senior-Level): four actions interviewers like to invite interviewees to execute

For more experienced developers, expect to discuss system architecture, especially if you’re aiming for a back-end, full-stack, or lead developer role.

You may be asked to:

1. Design a RESTful API or a microservice using C# and ASP.NET Core.

2. Sketch out how you would structure a scalable, maintainable application.

3. Discuss how you would handle authentication, data persistence, caching, and error handling.

4. Evaluate trade-offs between synchronous and asynchronous operations, or monolith vs microservice approaches.

Got a C# Development Interviewer? Congrats! Just keep in mind that the interviewer will want to understand how you approach performance, scalability, testability, and security within the .NET ecosystem.

3. Unit Testing and TDD: three typical interview tasks

Testing is a critical part of modern software development. You might be asked to:

i) Write unit tests using MSTest, NUnit, or xUnit.

ii) Apply mocking frameworks like Moq.

iii) Demonstrate understanding of Test-Driven Development (TDD) practices.

Don’t skimp on this part of your C# Development interview preparation! Being able to explain the purpose of unit, integration, and end-to-end tests, and where each one fits in, can be a deciding factor.

4. Database and SQL Knowledge: factor in at least 1 of these 4

Since many C# applications interact with a database, especially using Entity Framework or Dapper, expect at least one component of the technical test to involve:

1. Writing SQL queries (SELECT, JOIN, GROUP BY).

2. Understanding of normalization, indexing, and transactions.

3. Possibly designing a simple relational database schema.

4. Working with ORMs like Entity Framework Core, writing LINQ queries, or handling migrations.

Expect to be kept on your toes! You may be asked to optimise a query or fix a slow-loading function.

5. Debugging and Code Review: a testing trio for C# job candidates

Some interviews include exercises that test your ability to read, understand, and improve code:

i) Spot bugs in a C# code snippet.

ii) Improve performance or readability.

iii) Refactor a class or method to follow SOLID principles.

These three tasks provide the interviewer(s) with insight into how you handle existing codebases and contribute to team quality standards.

6. Concurrency, Async/Await and Multithreading: 4 oft-asked interview queries

Especially in backend-focused roles, expect to be tested on your understanding of:

1. async and await patterns.

2. Task parallelism (Task.Run,Parallel.ForEach, etc.).

3. Thread safety and locking (lock, Monitor, SemaphoreSlim, etc.).

4. Managing resource contention or deadlocks.

Why these four?! Well, understanding these advanced features demonstrates that you’re ready to handle scalable and responsive applications.

7. Soft Skills & Communication: 3 non-technical probes you may face

Though not always part of a "technical" test for C# Developer jobs, interviewers may assess how you communicate your thought process to others:

i) Are you able to explain why you chose a particular solution?

ii) Can you describe trade-offs clearly?

iii) Do you collaborate well when pair-programming?

Remember – clear and confident communication is often just as important as technical brilliance to succeed as a C# Developer.

C# Developer: How to prep for technical interview: 5 must-dos

1. Practice common C# challenges on LeetCode, Codewars, or HackerRank.

2. Brush up on .NET Core, including new features and best-practices.

3. Review design patterns,  such as Factory, Singleton, Repository, etc.

4. Use version control (Git) in your test submissions, if allowed.

5. Ask questions if a test scenario is unclear, show that you’re thoughtful and not afraid to clarify assumptions.

TLDR: C# Development job interview prep be like…

A technical interview test for a freelance or full-time C# developer role is about much more than just writing clean code.

In 2025, it’s increasingly about demonstrating your understanding of the C# language, design patterns, software architecture, testing methodologies, and collaboration mindset.

By preparing strategically across these five key areas, you’ll be well-positioned to impress and stand out from the competition.