How would you design consistent error handling across an ASP.NET Core API?

Design a consistent error handling strategy for ASP.NET Core APIs

Design API error handling across validation errors, conflicts, auth failures, not-found responses, and unexpected exceptions.

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I use one error-handling boundary to translate known failures into consistent HTTP responses. Validation, not-found, conflict, authorization, rate-limit, and unexpected failures each have a deliberate status and machine-readable code. Controllers return normal results or raise known application failures instead of building ad hoc error objects. Unexpected exceptions are logged and returned as safe generic problems.

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error contracts, ProblemDetails, exception boundaries, safe logging, client behavior, and retry semantics

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Design API error handling across validation errors, conflicts, auth failures, not-found responses, and unexpected exceptions. It matters in real backend work because the server has to enforce trust boundaries even when the UI, client, or caller behaves unexpectedly. The practical angle is error contracts, ProblemDetails, exception boundaries, safe logging, client behavior, and retry semantics, tied to a concrete production decision.
I use one error-handling boundary to translate known failures into consistent HTTP responses. Validation, not-found, conflict, authorization, rate-limit, and unexpected failures each have a deliberate status and machine-readable code. Controllers return normal results or raise known application failures instead of building ad hoc error objects. Unexpected exceptions are logged and returned as safe generic problems.
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The mapping preserves useful distinctions without exposing implementation details. A concurrency exception can become 409 with a recovery hint, while an invalid command becomes 400 or 422 with field errors. I use as the envelope, add a stable code and correlation id, and keep messages safe for clients. Domain and application layers do not depend on HTTP; the API boundary owns the translation. Tests assert both the status and the response contract for each important failure path.

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Returning 200 with error payloads
Leaking stack traces
Catching everything and returning BadRequest
Different error shapes per endpoint
Making clients parse strings

How would you design consistent error handling across an ASP.NET Core API?

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