Modern .NET is a different platform from the legacy .NET Framework many resumes were built on, and the interview needs to establish which one your candidate actually knows. These questions probe async discipline, EF Core judgment, and ASP.NET Core architecture, with notes on what strong answers cover.
What a strong answer covers
The method yields and resumes via a state machine rather than blocking a thread. Classic sins: sync-over-async with .Result or .Wait() causing deadlocks and thread starvation, async void outside event handlers, and forgetting cancellation tokens. ConfigureAwait nuance in library versus app code is a bonus.
What a strong answer covers
Singleton, scoped, transient, and the classic failure: a scoped DbContext captured by a singleton, or transient services holding expensive resources. The war story matters — lifetime bugs are subtle and everyone with real mileage has one.
What a strong answer covers
The change tracker snapshots entities for update detection; AsNoTracking for read-only queries to cut memory and CPU. Strong candidates extend to projection with Select to avoid loading full entities and know SaveChanges batching behavior.
What a strong answer covers
Log the generated SQL, examine the query plan, check for N+1 lazy loading, client-side evaluation, missing indexes, and cartesian explosion from multiple Includes with AsSplitQuery as a fix. Falling back to raw SQL or a stored procedure for hot paths, measured, is a legitimate ending.
What a strong answer covers
An ordered chain of delegates each choosing to short-circuit or call next; order matters (exception handling early, auth before endpoints). Real examples: correlation IDs, tenant resolution, request logging, rate limiting. Knowing built-ins before reinventing them is the judgment test.
What a strong answer covers
Allocation pressure and GC cost: structs for small, short-lived data, boxing traps in old collections and interfaces, Span<T> and Memory<T> for allocation-free slicing in hot paths. The senior version cites measuring with profilers or BenchmarkDotNet before optimizing.
What a strong answer covers
The layered configuration system — appsettings, environment variables, user secrets in development, a vault service in production — with the options pattern and validation on startup. Connection strings in source control is the disqualifying pattern.
What a strong answer covers
Separation of domain from infrastructure, some flavor of clean or vertical-slice architecture held pragmatically, hosted services or a job runner for background work, and shared kernel libraries. Dogmatic layer proliferation for a small product is itself a yellow flag; listen for proportion.
What a strong answer covers
xUnit or NUnit with mocking where it earns its keep, WebApplicationFactory for in-memory integration tests of the real pipeline, and Testcontainers or a real database for data-layer tests rather than trusting the EF in-memory provider. Distrust of the in-memory provider is a known-good signal.
What a strong answer covers
Audit dependencies with upgrade tooling, target .NET Standard for shared libraries, strangle incrementally — new services on modern .NET, API surface carved out — versus in-place upgrade depending on coupling. Windows-only dependencies like WCF and System.Web need named replacement strategies.
What a strong answer covers
Generational collection, the large object heap, server versus workstation GC modes. Caring moments: memory leaks from event handler references or static caches, LOH fragmentation, pause-sensitive workloads. Tooling fluency — dotnet-counters, dumps, PerfView — beats theory recital.
What a strong answer covers
Minimal APIs for small focused services, controllers for larger surfaces wanting filters and conventions — with the gap narrowing every release. gRPC for internal service-to-service contracts and streaming, REST for public and browser-facing APIs. Reasoned defaults, not fashion.
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Try the interview question generator →Ask the migration and minimal-API questions and listen for tense: candidates current on modern .NET talk about minimal APIs, built-in DI, and cross-platform deployment as daily reality. Framework-era candidates center IIS, Web Forms or MVC 5, and Windows-only patterns.
Only partially. The language, async, and memory questions transfer; the ASP.NET Core and EF questions do not. For game work, use our Unity question set instead — the runtime, frame-budget, and asset questions matter far more there.
A code review of a small ASP.NET Core service with planted issues: a sync-over-async call, a scoped service injected into a singleton, an untracked N+1 query. Review exercises test exactly the judgment these questions probe, in less time than a build-from-scratch task.
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