Other 4xx codes
All HTTP status codes in ASP.NET Core
4xx Client error
418 I'm a teapot
An April Fools' joke from RFC 2324. RFC 9110 reserves the code so nobody gives it a real meaning.
In ASP.NET Core: Do not use it in a real API.
418 in .NET
The StatusCodes constant, HttpStatusCode enum name, reason phrase, class, and how EnsureSuccessStatusCode() and the standard resilience handler treat 418.
| Constant | StatusCodes.Status418ImATeapot |
|---|---|
| HttpStatusCode | none; use (HttpStatusCode)418 |
| Reason phrase | Kestrel sends I'm a teapot; HttpClient's ReasonPhrase is null |
| Class | 4xx, client error |
| IsSuccessStatusCode | false |
| EnsureSuccessStatusCode() | throws HttpRequestException: Response status code does not indicate success: 418. |
| Standard resilience handler | does not retry it |
Returning 418
Minimal APIs
Results.StatusCode(StatusCodes.Status418ImATeapot)
Results.Problem(statusCode: StatusCodes.Status418ImATeapot, detail: "...")Controllers
StatusCode(StatusCodes.Status418ImATeapot)
Problem(statusCode: StatusCodes.Status418ImATeapot, detail: "...")The ProblemDetails body
What Results.Problem(statusCode: 418) sends (with AddProblemDetails()), as application/problem+json:
{
"title": "I'm a teapot",
"status": 418,
"traceId": "0HNA1B2C3D4E5:00000001"
}A controller's Problem(statusCode: 418) sends a different body, because MVC only fills type and title for codes in ApiBehaviorOptions.ClientErrorMapping:
{
"status": 418,
"traceId": "0HNA1B2C3D4E5:00000001"
}A bare StatusCode(418) in an [ApiController] also gets a ProblemDetails body automatically; Results.StatusCode(418) in a minimal API sends an empty body unless you add UseStatusCodePages().
Every response on this page was recorded from ASP.NET Core 10.0.12 on Kestrel in the Production environment; the HttpClient rows come from .NET 10.0.12 and Microsoft.Extensions.Http.Resilience 10.10.0.