Introduction
As .NET developers gain experience, interviews focus more on how applications behave rather than basic syntax. The questions below cover everyday concepts developers already use—API responses, configuration, startup, external calls, and error handling—but often without fully understanding why they work the way they do.
Each question is explained simply, with a small example, to make the behavior clear and interview-ready.
1. How Should an ASP.NET Core API Return Responses – IActionResult or ActionResult<T>?
An API response can be returned either as a flexible HTTP result or as a strongly typed result.
IActionResult returns only the HTTP response information such as status codes and messages.
public IActionResult GetUser()
{
return Ok("User");
}
ActionResult<T> returns the HTTP response along with a known data type.
public ActionResult<User> GetUser()
{
return Ok(new User { Id = 1, Name = "John" });
}
ActionResult<T> improves type safety, readability, and API documentation.
2. How Should HttpClient Be Used to Call External APIs Safely?
HttpClient manages network connections and should not be created repeatedly.
Creating a new instance each time opens many connections and can cause performance issues.
var client = new HttpClient();
Registering HttpClient through dependency injection allows safe reuse.
builder.Services.AddHttpClient();
This approach enables connection pooling and efficient resource management.
3. How Are Application Settings Managed Using appsettings.json?
Application values such as connection strings and API keys are stored outside the code.
Example configuration file:
{
"ConnectionStrings": {
"DefaultConnection": "Server=..."
}
}
Reading values in code:
var connectionString =
configuration.GetConnectionString("DefaultConnection");
This separation allows easy changes across environments without code changes.
4. How Does ASP.NET Core Start an Application – ConfigureServices vs Configure?
Application startup happens in two stages.
ConfigureServices prepares the application by registering required services.
builder.Services.AddControllers();
Configure defines how requests flow through middleware.
app.UseAuthorization();
app.MapControllers();
One stage prepares dependencies, the other controls request execution.
5. How Should Exceptions Be Handled in ASP.NET Core Applications?
Handling errors in every method leads to duplicated code and inconsistent responses.
try
{
var user = _context.Users.First();
}
catch
{
return BadRequest();
}
Centralized exception handling manages errors in one place.
app.UseExceptionHandler("/error");
This keeps controllers clean and ensures consistent error handling.
Conclusion:
These questions are commonly asked because they reflect real-world decisions made while building .NET applications. Understanding the reasons behind these concepts makes interview answers clear and confident. I hope this will help you.