What is Middleware in ASP.NET Core?

Middleware in ASP.NET Core is a software component that handles HTTP requests and responses as they move through the application pipeline.

Simple Definition

Middleware acts like a pipeline of components where each one can:

• Process an incoming request
• Modify it
• Pass it to the next component
• Or stop the request and return a response

How It Works

When a request comes into an ASP.NET Core app:

1. It enters the middleware pipeline
2. Each middleware component runs in sequence

Each can either:

• Call the next middleware
• Or handle the request and end the pipeline

Key Features

• Request/Response handling
• Modular and reusable
• Order matters (execution depends on registration order)
• Can short-circuit the pipeline

Common Built-in Middleware

• Authentication Middleware
• Authorization Middleware
• Exception Handling Middleware
• Static File Middleware
• Routing Middleware

Example

public void Configure(IApplicationBuilder app)
{
    app.Use(async (context, next) =>
    {
        await context.Response.WriteAsync("Hello ");
        await next();
        await context.Response.WriteAsync("World!");
    });
}

Output: Hello World!

In Short

Middleware in ASP.NET Core is the core mechanism that processes HTTP requests in a step-by-step pipeline, allowing developers to control how requests and responses are handled.