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title	author	description	monikerRange	ms.author	ms.custom	ms.date	uid
Handle errors in ASP.NET Core web APIs	pranavkm	Learn about error handling with ASP.NET Core web APIs.	>= aspnetcore-2.1	prkrishn	mvc	09/27/2019	web-api/handle-errors

Handle errors in ASP.NET Core web APIs

This article describes how to handle and customize error handling with ASP.NET Core web APIs.

View or download sample code (How to download)

Developer Exception Page

The Developer Exception Page 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:

[!code-csharp]

Run the following curl command to test the preceding action:

curl -i https://localhost:5001/weatherforecast/chicago

::: moniker range=">= aspnetcore-3.0"

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:

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
   at lambda_method(Closure , Object , Object[] )
   at Microsoft.Extensions.Internal.ObjectMethodExecutor.Execute(Object target, Object[] parameters)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.SyncObjectResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Logged|12_1(ControllerActionInvoker invoker)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeNextActionFilterAsync>g__Awaited|10_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeInnerFilterAsync()
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeFilterPipelineAsync>g__Awaited|19_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Logged|17_1(ResourceInvoker invoker)
   at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)
   at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)

HEADERS
=======
Accept: */*
Host: localhost:44312
User-Agent: curl/7.55.1

To display an HTML-formatted response instead, set the Accept HTTP request header to the text/html media type. For example:

curl -i -H "Accept: text/html" https://localhost:5001/weatherforecast/chicago

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:

::: moniker-end

HTTP/1.1 500 Internal Server Error
Transfer-Encoding: chunked
Content-Type: text/html; charset=utf-8
Server: Microsoft-IIS/10.0
X-Powered-By: ASP.NET
Date: Fri, 27 Sep 2019 16:55:37 GMT

<!DOCTYPE html>
<html lang="en" xmlns="http://www.w3.org/1999/xhtml">
    <head>
        <meta charset="utf-8" />
        <title>Internal Server Error</title>
        <style>
            body {
    font-family: 'Segoe UI', Tahoma, Arial, Helvetica, sans-serif;
    font-size: .813em;
    color: #222;
    background-color: #fff;
}

::: moniker range=">= aspnetcore-3.0"

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:

::: moniker-end

[!WARNING] 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 can be used to produce an error payload:

In Startup.Configure, invoke xref:Microsoft.AspNetCore.Builder.ExceptionHandlerExtensions.UseExceptionHandler* to use the middleware:

::: moniker range=">= aspnetcore-3.0"

[!code-csharp]

::: moniker-end

::: moniker range="<= aspnetcore-2.2"

[!code-csharp]

::: moniker-end
Configure a controller action to respond to the /error route:

::: moniker range=">= aspnetcore-3.0"

[!code-csharp]

::: moniker-end

::: moniker range="<= aspnetcore-2.2"

[!code-csharp]

::: moniker-end

The preceding Error action sends an 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:

In Startup.Configure, register environment-specific Exception Handling Middleware instances:

::: moniker range=">= aspnetcore-3.0"

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    if (env.IsDevelopment())
    {
        app.UseExceptionHandler("/error-local-development");
    }
    else
    {
        app.UseExceptionHandler("/error");
    }
}

::: moniker-end

::: moniker range="<= aspnetcore-2.2"

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    if (env.IsDevelopment())
    {
        app.UseExceptionHandler("/error-local-development");
    }
    else
    {
        app.UseExceptionHandler("/error");
    }
}

::: moniker-end

In the preceding code, the middleware is registered with:

A route of /error-local-development in the Development environment.
A route of /error in environments that aren't Development.

Apply attribute routing to controller actions:

::: moniker range=">= aspnetcore-3.0"

[!code-csharp]

::: moniker-end

::: moniker range="<= aspnetcore-2.2"

[!code-csharp]

::: moniker-end

Use exceptions to modify the response

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:

Create a well-known exception type named HttpResponseException:

[!code-csharp]
Create an action filter named HttpResponseExceptionFilter:

[!code-csharp]
In Startup.ConfigureServices, add the action filter to the filters collection:

::: moniker range=">= aspnetcore-3.0"

[!code-csharp]

::: moniker-end

::: moniker range="= aspnetcore-2.2"

[!code-csharp]

::: moniker-end

::: moniker range="= aspnetcore-2.1"

[!code-csharp]

::: moniker-end

Validation failure error response

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:

::: moniker range=">= aspnetcore-3.0"

[!code-csharp]

::: moniker-end

::: moniker range="= aspnetcore-2.2"

[!code-csharp]

::: moniker-end

::: moniker range="= aspnetcore-2.1"

[!code-csharp]

::: moniker-end

Client error response

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:

Implement ProblemDetailsFactory
Use ApiBehaviorOptions.ClientErrorMapping

Implement ProblemDetailsFactory

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:

public void ConfigureServices(IServiceCollection serviceCollection)
{
    services.AddControllers();
    services.AddTransient<ProblemDetailsFactory, CustomProblemDetailsFactory>();
}

::: moniker-end

::: moniker range="= aspnetcore-2.2"

The error response can be configured as outlined in the Use ApiBehaviorOptions.ClientErrorMapping section.

::: moniker-end

::: moniker range=">= aspnetcore-2.2"

Use ApiBehaviorOptions.ClientErrorMapping

Use the xref:Microsoft.AspNetCore.Mvc.ApiBehaviorOptions.ClientErrorMapping* property to configure the contents of the ProblemDetails response. For example, the following code in Startup.ConfigureServices updates the type property for 404 responses:

::: moniker-end

::: moniker range=">= aspnetcore-3.0"

[!code-csharp]

::: moniker-end

::: moniker range="= aspnetcore-2.2"

[!code-csharp]

::: moniker-end

13 KiB Raw Blame History

Handle errors in ASP.NET Core web APIs

Developer Exception Page

Exception handler

Use exceptions to modify the response

Validation failure error response

Client error response

Implement ProblemDetailsFactory

Use ApiBehaviorOptions.ClientErrorMapping

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