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What are exception filters (when) and why use them? How do custom exception classes work in C#, and what's the recommended convention for creating one? What is exception filtering using the 'when' clause, and what advantage does it offer over catching and manually re-throwing? Why does 'throw;' (bare throw) preserve the original stack trace, while 'throw ex;' does not? What is the recommended strategy for exceptions in a layered/enterprise app? How does exception handling interact with async/await, and how are exceptions from an async Task propagated to the awaiting caller? How does AggregateException work with Task.WhenAll() when multiple concurrent tasks throw exceptions? What is 'exception filtering with side effects' and why is it considered a controversial but sometimes useful technique for logging? How would you design a robust global exception handling middleware in ASP.NET Core to convert unhandled exceptions into consistent API error responses? How does exception performance (throwing/catching) compare to normal control flow, and why should exceptions generally NOT be used for expected, routine control flow?
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C# › Exception Handling

When should you create custom exceptions vs use built-in ones?

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Create a custom exception when callers need to catch a domain-specific condition distinctly; otherwise reuse built-ins (ArgumentException, InvalidOperationException). Keep a meaningful hierarchy.
public class InsufficientFundsException(decimal shortfall) : Exception;
Real-world example A banking layer throws InsufficientFundsException so the API can map it to a 422 response.
All 16 Exception Handling questions