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How to handle errors in Minimal API apps

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This article describes how to handle errors in Minimal API apps.

Exceptions

In a Minimal API app, there are two different built-in centralized mechanisms to handle unhandled exceptions:

This section refers to the following Minimal API app to demonstrate ways to handle exceptions. It throws an exception when the endpoint /exception is requested:

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.Map("/exception", () 
    => { throw new InvalidOperationException("Sample Exception"); });

app.Run();

Developer Exception Page

The Developer Exception Page shows detailed stack traces for server errors. It uses DeveloperExceptionPageMiddleware to capture synchronous and asynchronous exceptions from the HTTP pipeline and to generate error responses.

ASP.NET Core apps enable the developer exception page by default when both:

For more information on configuring middleware, see Middleware in Minimal API apps.

Using the preceding Minimal API app, when the Developer Exception Page detects an unhandled exception, it generates a default plain-text response similar to the following example:

HTTP/1.1 500 Internal Server Error
Content-Type: text/plain; charset=utf-8
Date: Thu, 27 Oct 2022 18:00:59 GMT
Server: Kestrel
Transfer-Encoding: chunked
 
    System.InvalidOperationException: Sample Exception
    at Program.<>c.<<Main>$>b__0_1() in ....:line 17
    at lambda_method2(Closure, Object, HttpContext)
    at Microsoft.AspNetCore.Routing.EndpointMiddleware.Invoke(HttpContext httpContext)
    --- End of stack trace from previous location ---
    at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddlewareImpl.Invoke(HttpContext context)
HEADERS
=======
Accept: */*
Connection: keep-alive
Host: localhost:5239
Accept-Encoding: gzip, deflate, br

Warning

Don't enable the Developer Exception Page unless the app is running in the Development environment. Don't share detailed exception information publicly when the app runs in production. For more information on configuring environments, see Use multiple environments in ASP.NET Core.

Exception handler

In non-development environments, use the Exception Handler Middleware to produce an error payload. To configure the Exception Handler Middleware, call UseExceptionHandler.

For example, the following code changes the app to respond with an RFC 7807-compliant payload to the client. For more information, see Problem Details section.

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.UseExceptionHandler(exceptionHandlerApp 
    => exceptionHandlerApp.Run(async context 
        => await Results.Problem()
                     .ExecuteAsync(context)));

app.Map("/exception", () 
    => { throw new InvalidOperationException("Sample Exception"); });

app.Run();

Client and Server error responses

Consider the following Minimal API app.

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.Map("/users/{id:int}", (int id) 
    => id <= 0 ? Results.BadRequest() : Results.Ok(new User(id)) );

app.Run();

public record User(int Id);

The /users endpoint produces 200 OK with a json representation of User when id is greater than 0, otherwise a 400 BAD REQUEST status code without a response body. For more information about creating a response, see Create responses in Minimal API apps.

The Status Code Pages middleware can be configured to produce a common body content, when empty, for all HTTP client (400-499) or server (500 -599) responses. The middleware is configured by calling the UseStatusCodePages extension method.

For example, the following example changes the app to respond with an RFC 7807-compliant payload to the client for all client and server responses, including routing errors (for example, 404 NOT FOUND). For more information, see the Problem Details section.

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.UseStatusCodePages(async statusCodeContext 
    =>  await Results.Problem(statusCode: statusCodeContext.HttpContext.Response.StatusCode)
                 .ExecuteAsync(statusCodeContext.HttpContext));

app.Map("/users/{id:int}", (int id) 
    => id <= 0 ? Results.BadRequest() : Results.Ok(new User(id)) );

app.Run();

public record User(int Id);

Problem details

Problem Details are not the only response format to describe an HTTP API error, however, they are commonly used to report errors for HTTP APIs.

The problem details service implements the IProblemDetailsService interface, which supports creating problem details in ASP.NET Core. The AddProblemDetails extension method on IServiceCollection registers the default IProblemDetailsService implementation.

In ASP.NET Core apps, the following middleware generates problem details HTTP responses when AddProblemDetails is called, except when the Accept request HTTP header doesn't include one of the content types supported by the registered IProblemDetailsWriter (default: application/json):

Minimal API apps can be configured to generate problem details response for all HTTP client and server error responses that don't have a body content yet by using the AddProblemDetails extension method.

The following code configures the app to generate problem details:

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddProblemDetails();

var app = builder.Build();

app.UseExceptionHandler();
app.UseStatusCodePages();

app.Map("/users/{id:int}", (int id) 
    => id <= 0 ? Results.BadRequest() : Results.Ok(new User(id)) );

app.Map("/exception", () 
    => { throw new InvalidOperationException("Sample Exception"); });

app.Run();

For more information on using AddProblemDetails, see Problem Details