[View or download sample code](https://github.com/aspnet/AspNetCore.Docs/tree/master/aspnetcore/web-api/handle-errors/samples) ([How to download](xref:index#how-to-download-a-sample))
The [Developer Exception Page](xref:fundamentals/error-handling) is a useful tool to get detailed stack traces for server errors. It uses <xref:Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware> to capture synchronous and asynchronous exceptions from the HTTP pipeline and to generate error responses. To illustrate, consider the following controller action:
In ASP.NET Core 3.0 and later, the Developer Exception Page displays a plain-text response if the client doesn't request HTML-formatted output. The following output appears:
```console
HTTP/1.1 500 Internal Server Error
Transfer-Encoding: chunked
Content-Type: text/plain
Server: Microsoft-IIS/10.0
X-Powered-By: ASP.NET
Date: Fri, 27 Sep 2019 16:13:16 GMT
System.ArgumentException: We don't offer a weather forecast for chicago. (Parameter 'city')
at WebApiSample.Controllers.WeatherForecastController.Get(String city) in C:\working_folder\aspnet\AspNetCore.Docs\aspnetcore\web-api\handle-errors\samples\3.x\Controllers\WeatherForecastController.cs:line 34
Consider the following excerpt from the HTTP response:
::: moniker-end
::: moniker range="<= aspnetcore-2.2"
In ASP.NET Core 2.2 and earlier, the Developer Exception Page displays an HTML-formatted response. For example, consider the following excerpt from the HTTP response:
The HTML-formatted response becomes useful when testing via tools like Postman. The following screen capture shows both the plain-text and the HTML-formatted responses in Postman:
> Enable the Developer Exception Page **only when the app is running in the Development environment**. You don't want to share detailed exception information publicly when the app runs in production. For more information on configuring environments, see <xref:fundamentals/environments>.
## Exception handler
In non-development environments, [Exception Handling Middleware](xref:fundamentals/error-handling) can be used to produce an error payload:
The preceding `Error` action sends an [RFC7807](https://tools.ietf.org/html/rfc7807)-compliant payload to the client.
Exception Handling Middleware can also provide more detailed content-negotiated output in the local development environment. Use the following steps to produce a consistent payload format across development and production environments:
1. In `Startup.Configure`, register environment-specific Exception Handling Middleware instances:
The contents of the response can be modified from outside of the controller. In ASP.NET 4.x Web API, one way to do this was using the <xref:System.Web.Http.HttpResponseException> type. ASP.NET Core doesn't include an equivalent type. Support for `HttpResponseException` can be added with the following steps:
1. Create a well-known exception type named `HttpResponseException`:
For web API controllers, MVC responds with a <xref:Microsoft.AspNetCore.Mvc.ValidationProblemDetails> response type when model validation fails. MVC uses the results of <xref:Microsoft.AspNetCore.Mvc.ApiBehaviorOptions.InvalidModelStateResponseFactory> to construct the error response for a validation failure. The following example uses the factory to change the default response type to <xref:Microsoft.AspNetCore.Mvc.SerializableError> in `Startup.ConfigureServices`:
An *error result* is defined as a result with an HTTP status code of 400 or higher. For web API controllers, MVC transforms an error result to a result with <xref:Microsoft.AspNetCore.Mvc.ProblemDetails>.
::: moniker range=">= aspnetcore-3.0"
The error response can be configured in one of the following ways:
MVC uses `Microsoft.AspNetCore.Mvc.ProblemDetailsFactory` to produce all instances of <xref:Microsoft.AspNetCore.Mvc.ProblemDetails> and <xref:Microsoft.AspNetCore.Mvc.ValidationProblemDetails>. This includes client error responses, validation failure error responses, and the `Microsoft.AspNetCore.Mvc.ControllerBase.Problem` and <xref:Microsoft.AspNetCore.Mvc.ControllerBase.ValidationProblem> helper methods.
To customize the problem details response, register a custom implementation of `ProblemDetailsFactory` in `Startup.ConfigureServices`:
```csharp
public void ConfigureServices(IServiceCollection serviceCollection)
The error response can be configured as outlined in the [Use ApiBehaviorOptions.ClientErrorMapping](#use-apibehavioroptionsclienterrormapping) section.
Use the <xref:Microsoft.AspNetCore.Mvc.ApiBehaviorOptions.ClientErrorMapping%2A> property to configure the contents of the `ProblemDetails` response. For example, the following code in `Startup.ConfigureServices` updates the `type` property for 404 responses:
