--- title: ".NET / C# Developer Interview Questions (2026): By Level, With Model Answers" url: https://weworkworldwide.com/net-developer-interview-questions/ description: ".NET and C# interview questions for junior, mid and senior developers — async, GC, EF Core and architecture, with model answers and the red flags to listen for." date: 2026-07-04T15:12:16+00:00 source: https://weworkworldwide.com/llms.txt --- # .NET / C# Developer Interview Questions (2026): By Level, With Model Answers How to use this C# gives you a lot of rope. These questions check whether a candidate understands the runtime — value vs reference types, async, garbage collection, EF Core — not just the syntax. Hiring a .NET developer is easy. Telling a real one from a convincing résumé is the hard part — and it’s most of what we do. These are grouped by level, because the same question that stretches a junior is a warm-up for a senior. ## Junior .NET interview questions 0–2 years Type system and async fundamentals. ### What’s the difference between value types and reference types? What a strong answer covers Value types (structs, `int`) hold their data directly and copy on assignment; reference types (classes) are on the heap and the variable holds a reference. They connect this to equality and mutation behaviour. Red flag Thinks everything is copied, or is unaware of the distinction entirely. ### What does `async`/`await` actually do? What a strong answer covers It frees the calling thread while an I/O operation completes, improving scalability under load; it is not automatically parallelism or a new thread. They know blocking on it with `.Result` risks deadlocks. Red flag Believes `async` spins up a thread, or blocks on async with `.Result`/`.Wait()`. ### What is deferred execution in LINQ? What a strong answer covers LINQ queries over `IEnumerable` don’t run until enumerated, so the same query can hit the database again each time you iterate it; materialising with `ToList()` executes it once. They avoid accidental re-execution. Red flag Enumerates a query repeatedly, unaware each pass re-runs it against the source. ## Mid-level .NET interview questions 2–5 years Memory, DI and async correctness. ### How does garbage collection relate to `IDisposable`? What a strong answer covers The GC reclaims managed memory in generations, but unmanaged resources (connections, file handles, sockets) must be released deterministically via `IDisposable` and `using`. They don’t rely on the GC for that. Red flag Never disposes connections or streams and assumes the GC handles unmanaged resources. ### Explain the service lifetimes in ASP.NET Core DI. What a strong answer covers `Transient`, `Scoped` and `Singleton`, chosen by how state should be shared; the classic bug is a captive dependency — injecting a scoped service into a singleton. They register deliberately. Red flag Registers everything as a singleton, or `new`s up dependencies instead of injecting them. ### How do you avoid async deadlocks? What a strong answer covers Go async all the way rather than blocking on `.Result`/`.Wait()`, and use `ConfigureAwait(false)` in library code to avoid capturing a synchronisation context. They understand where deadlocks come from. Red flag Mixes blocking and async calls and can’t explain the resulting deadlock. ## Senior .NET interview questions 5+ years EF Core, performance and architecture. ### What EF Core pitfalls have you hit at scale? What a strong answer covers N+1 queries, change-tracking overhead (`AsNoTracking` for reads), lazy-loading surprises, and projecting to DTOs instead of loading full entities. They profile the generated SQL. Red flag Unaware of N+1, loads whole tables and loops in memory. ### How do you design a high-throughput ASP.NET Core service? What a strong answer covers Async I/O end to end, minimal allocations, caching, tuned EF queries, connection pooling, and profiling under realistic load. They know where the time actually goes. Red flag Synchronous I/O, N+1 queries and no measurement. ### How do you structure a large .NET solution? What a strong answer covers Layered or clean architecture that separates domain from infrastructure, keeps business logic out of controllers, and defines DI boundaries for testability. Structure driven by dependencies, not folders. Red flag Business logic living in controllers with no layering. **Skip the screening entirely.**We vet .NET engineers so you don’t have to — embed one in your team, or have us build it. [Hire .NET developers](https://weworkworldwide.com/hire-remote-net-developers/)[Compare us](https://weworkworldwide.com/compare/) Browse the full series on the [interview questions hub](https://weworkworldwide.com/interview-questions/), or see how we assess engineers in our [interview process](https://weworkworldwide.com/how-we-interview-engineers/).