Create your own custom middleware in ASP.NET Core

You've heard of middleware in ASP.NET Core, but don't know what it is. This tutorial will show you what it is, or you can watch the video:

Download the code example

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Software

This is the software that will need to be installed onto your machine.

• Visual Studio 2026. Version 18.0.0 or above. It will work with the free community version.

• .NET 10 SDK. Version 10.0.0 or above.

The application

Open up RoundTheCode.Middleware.slnx in Visual Studio.

A custom middleware class has been added in RequestLoggingMiddleware.cs. This returns a 503 Service Unavailable response for all requests if the MaintenancePage property is set to true.

It also fires off a background task once the response is completed. It will wait 5 seconds before myScopedService.Test() is called.

You can see this by running the application. If MaintenancePage is set to false, it will load the Swagger documentation at https://localhost:7170/swagger. Open up the Console window and see that myScopedService.Test() has been called for each request.

If MaintenacePage is set to true, https://localhost:7170/swagger will just output "This page is currently unavailable".