Why should you care?

Different situations need different responses — a form save redirects, an API call returns JSON, a missing product returns NotFound.

See it live — copy this example

Create an MVC project (dotnet new mvc), add the code, and run dotnet run.

public IActionResult Demo(int id)
{
  if (id <= 0) return BadRequest();
  var item = _service.Find(id);
  if (item == null) return NotFound();
  if (Request.Headers.Accept == "application/json")
      return Json(item);
  return View(item);
}

Run Example »

Edit the code and click Run — like W3Schools Try it Yourself.

What happened?

• View() renders Razor.
• RedirectToAction sends a 302 to another page.
• Json() serializes to JSON for AJAX.
• NotFound() is HTTP 404.

Try it yourself

1. Return View() from Index — confirm HTML.
2. Return RedirectToAction("Index") from an action — watch URL change.
3. Return Json(new { ok = true }) and open URL in browser — see JSON.
4. Change text or labels in the example and run again — watch the browser update.
5. Break the code on purpose (remove a semicolon), read the error message, then fix it.

Remember

IActionResult = flexible response type. View, Redirect, Json, NotFound are the common ones. Pick the result that matches what the user or client expects.