Controller action return types in ASP.NET Core web API

▤ Summary

This article explains the return type options available for ASP.NET Core Web API controller actions. It compares specific types, IEnumerable and IAsyncEnumerable, IActionResult, ActionResult<T>, IResult, and typed result unions. It shows how each option affects response metadata, performance, and compile-time safety. It also highlights when to use [ProducesResponseType] and when the framework can infer endpoint metadata automatically.

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