.NET developer screening questions for recruiters

For a .NET developer, the first screen needs to pin down which .NET the candidate actually works in, what they built with it, and whether their answers get more specific when you push. Plan on 15 to 20 minutes. You don't need to read C# to hear the difference.

What does a .NET developer do?

A .NET developer builds software on Microsoft's .NET platform, almost always in C#: web APIs with ASP.NET Core, internal business apps, background services and some Windows desktop apps. The Bureau of Labor Statistics groups them with software developers, who "design computer applications or programs" and keep them working through maintenance and testing.

Version matters this year. Microsoft's support policy lists .NET 10 as the current long-term support release, and both .NET 8 and .NET 9 reach end of support on 10 November 2026, so many teams are mid-upgrade. Older apps often still run on .NET Framework 4.x, the Windows-only predecessor. Ask the hiring manager which one the team uses.

Which skills should you check at each level?

What screening questions should you ask a .NET developer?

Swap in the team's own stack where it differs.

Which version of .NET did you use on your last project, and what was the app?

This separates modern .NET from .NET Framework experience and anchors the rest of the screen in one real project.

Strong answer: names a version (for example .NET 8, or .NET Framework 4.8 for an older app), the type of app, where it ran (IIS, Azure App Service, containers) and which part they owned.

Weak answer: "I've worked with all versions of .NET," with no project attached.

Tell me about an API endpoint you built in ASP.NET Core. How did a request get from the caller to the database and back?

Walking through one request shows whether they built it or watched someone else build it.

Strong answer: describes the steps in order: a controller or minimal API route, input validation, a service class, Entity Framework Core or Dapper for the query, then the response and status code. They mention error handling or authentication.

Weak answer: "I created REST APIs using .NET Core and SQL Server."

A page makes the same database query dozens of times on one load. What is Entity Framework probably doing, and how do you fix it?

Entity Framework Core is on many .NET job descriptions, and this problem (often called an N+1 query) is a common one.

Strong answer: suspects lazy loading or a query inside a loop, checks the generated SQL in the logs or a profiler, then loads related data up front with Include or a projection.

Weak answer: "Add caching" or "move to a faster database," without looking at the queries first.

What does async and await buy you in a web API, and when have you seen it go wrong?

Misused async code can make a .NET service slow down or hang under load.

Strong answer: explains that the server can handle other requests while it waits on a database or HTTP call. They name a real mistake such as calling .Result or .Wait() and causing a hang, or an async void method whose exception the caller can't catch and that can crash the process.

Weak answer: "It makes the code run faster" or "it runs things in parallel."

Have you upgraded an app from .NET Framework to modern .NET, or between .NET versions? What broke?

Many teams are upgrading right now, with .NET 8 and 9 support ending on 10 November.

Strong answer: names real blockers, such as code tied to System.Web, WCF services, old NuGet packages, or settings moving from web.config to appsettings.json, and explains how they tested and released the change.

Weak answer: "We changed the target framework and it worked." That can be true for a small version bump, so ask what they tested.

Tell me about a production bug in a .NET app that you tracked down yourself.

This shows ownership and how they debug when the answer isn't obvious.

Strong answer: a specific symptom, the tools they used (Application Insights, structured logs, the Visual Studio debugger, a memory dump), the cause, the fix and how they confirmed it.

Weak answer: a team story where you can't tell what they personally did.

What red flags should you note?

• The resume lists WPF, WCF, Web Forms, Blazor, MAUI and Azure Functions at the same depth, and the candidate can describe none of them in detail.
• They can't say whether their last project ran on .NET Framework or modern .NET.
• Every answer sounds like Microsoft's documentation: correct definitions, no example from their own work.
• The role needs ASP.NET Core APIs and all their recent work is Web Forms. Fine for a legacy role; otherwise, note the mismatch.
• Detail collapses at the second follow-up question.

Treat each of these as a reason to probe in your own call. If you're worried someone else is answering for the candidate, read how to spot a proxy interview.

How do you run this screen with Simplehire?

Create the role and add the must-haves you agreed with the hiring manager as its required skills, for example C#, ASP.NET Core, Entity Framework Core and SQL Server. If the client is mid-upgrade, add the upgrade as its own skill, for example "migration from .NET Framework to .NET 10". The candidate talks with our AI interviewer in the browser, and the report arrives when they finish.

Below the verdict, Skills demonstrated X/Y counts how many of your required skills the candidate demonstrated, and Areas to probe lists what to raise in your own call. You decide who moves forward. Every screen runs in enforced full-screen with copy and paste restricted or flagged and tab switches recorded. For remote roles you can also require an ID check or a second device; a person reviews every alert before any decision is made.

With 25 free Basic screens a month and no credit card needed, you can put your next few .NET applicants through Basic before paying anything (pricing). For roles that lean toward hosting, use the Azure cloud engineer questions; for roles that include the front end, the full-stack developer questions.