Middleware vs Filters: A Guide for Cross-Cutting Concerns

When building modern web applications in ASP.NET Core, we constantly deal with “cross-cutting concerns.” These are the essential but repetitive tasks that cut across our application’s features: logging, authentication, authorization, caching, and error handling. The framework gives us two powerful tools for this job: Middleware and Filters.

While both can solve similar problems, they operate at different levels of the application stack. A common point of confusion for developers is choosing the right tool. Let me be direct: for truly global, application-wide cross-cutting concerns, Middleware is almost always the superior choice.

This post will break down why Middleware holds a strategic advantage over Filters for these scenarios and clarify when Filters still have their essential place.

Understanding the Players: The Pipeline is Everything

The key to this discussion is understanding where Middleware and Filters live within the ASP.NET Core request processing pipeline.

What is Middleware?

Think of Middleware as a series of components chained together to form the fundamental request and response pipeline. Each piece of middleware inspects an incoming HttpContext, performs an action, and then either passes the request to the next component in the chain or short-circuits the process by generating a response itself.

It’s low-level, efficient, and completely agnostic of what will ultimately handle the request. It doesn’t know about MVC controllers, Razor Pages, or Minimal API handlers; it only knows about the HttpContext.

Here’s a simple middleware component that logs the request path and a custom header:

// A simple custom middleware class
public class RequestLoggingMiddleware
{
    private readonly RequestDelegate _next;
    private readonly ILogger<RequestLoggingMiddleware> _logger;

    public RequestLoggingMiddleware(RequestDelegate next, ILogger<RequestLoggingMiddleware> logger)
    {
        _next = next;
        _logger = logger;
    }

    public async Task InvokeAsync(HttpContext context)
    {
        var correlationId = context.Request.Headers["X-Correlation-ID"].FirstOrDefault() ?? Guid.NewGuid().ToString();
        _logger.LogInformation(
            "Request starting: {Method} {Path} | CorrelationId: {CorrelationId}",
            context.Request.Method,
            context.Request.Path,
            correlationId);

        // Call the next middleware in the pipeline
        await _next(context);

        _logger.LogInformation("Request finished with status code: {StatusCode}", context.Response.StatusCode);
    }
}

// Registering it in Program.cs (using an extension method for cleanliness)
// public static IApplicationBuilder UseRequestLogging(this IApplicationBuilder builder)
// {
//     return builder.UseMiddleware<RequestLoggingMiddleware>();
// }

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

app.UseRequestLogging(); // Our middleware is registered here

app.MapGet("/", () => "Hello World!");

app.Run();

The order of registration in Program.cs is the order of execution. This simple, linear flow is a core strength.

What are Filters?

Filters, on the other hand, are part of a higher-level pipeline: the MVC/API action invocation pipeline. They execute at specific stages around the execution of an action method.

They come in several flavors:

• Authorization Filters: Run first to determine if a user is authorized.
• Resource Filters: Run after authorization, ideal for short-circuiting or caching.
• Action Filters: Run immediately before and after an action method executes.
• Exception Filters: Apply global error-handling policies for exceptions in the MVC pipeline.
• Result Filters: Run before and after a result is executed.

The crucial difference is that Filters have access to a rich, high-level context, such as ActionExecutingContext or ResultExecutingContext, which provides details about the target controller, action method, arguments, and model state.

Here’s an Action Filter that validates the model state before an action executes:

using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Filters;

public class ValidateModelStateAttribute : ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext context)
    {
        if (!context.ModelState.IsValid)
        {
            context.Result = new BadRequestObjectResult(context.ModelState);
        }

        base.OnActionExecuting(context);
    }
}

// Used on a controller action
[ApiController]
[Route("api/[controller]")]
public class ProductsController : ControllerBase
{
    [HttpPost]
    [ValidateModelState] // Filter is applied here
    public IActionResult Create(ProductCreateModel model)
    {
        // Logic will only run if the model is valid
        return Ok();
    }
}

Why Middleware Often Wins for Global Concerns

Now that we’ve set the stage, let’s explore the key reasons Middleware is a better fit for broad, cross-cutting concerns.

1. Performance and Lower Overhead

Middleware is fundamentally more lightweight. It’s invoked very early in the request lifecycle, often before significant processing like routing or model binding has even occurred. The context it operates on (HttpContext) is relatively simple.

Filters, by contrast, are part of the feature-rich MVC/API framework. Before a filter can run, the framework has to do more work:

• Route matching to identify the controller and action.
• Controller and filter instantiation (dependency injection).
• Model binding and validation.

This all adds up to a small but measurable overhead. For high-throughput services where every microsecond counts, handling a concern like rate-limiting in Middleware before the MVC/API pipeline even spins up is a significant performance win.

From the Trenches: I once worked on a public API gateway that was struggling under load. We moved our custom API key validation logic from a global Action Filter to a dedicated piece of Middleware. The performance improvement was immediate and noticeable. By rejecting invalid requests before the expensive MVC machinery was ever involved, we dramatically reduced CPU and memory pressure on the servers.

2. Scope and Universality

This is perhaps the most compelling argument. Middleware is universal. It applies to every single request that your application handles, regardless of the endpoint type:

• MVC Controller Actions
• Razor Pages
• Minimal API Endpoints
• gRPC Services
• Static Files (e.g., JavaScript, CSS, images)
• Health Checks

A logging middleware will log a request for index.html just as it would for /api/users. A security header middleware will add headers to every response. This makes it the only truly reliable place for application-wide policies.

Filters are scoped exclusively to the MVC/API pipeline. They will not run for static file requests, gRPC calls, or health check endpoints unless you take extra, often complex, steps. If you put your logging logic in a global filter, you’re missing a huge chunk of your application’s traffic.

3. Absolute Pipeline Control and Short-Circuiting

Middleware has ultimate control over the request pipeline. At any point, a middleware component can choose not to call await _next(context) and instead write a response directly.

This is incredibly powerful for concerns that need to halt a request early:

• Authentication/Authorization: If a user isn’t authenticated, stop everything and return a 401 Unauthorized.
• Rate Limiting: If a client exceeds their quota, stop and return a 429 Too Many Requests.
• Static Caching: If a cached version of a response exists, serve it immediately without touching any application logic.

While filters can also short-circuit by setting the context.Result, it happens much later. Middleware can stop a request before routing even runs, saving valuable resources.

4. Simplicity and Predictable Order

The middleware pipeline is defined in one place: Program.cs. It’s a simple, linear chain. The order you see app.Use... calls is the order of execution. This makes it very easy to reason about the flow of a request and debug issues.

Filter execution order, however, can be surprisingly complex. It depends on the filter type, scope (Global, Controller, Action), and the explicit Order property. It’s not always obvious which filter will run when, especially in a large application with filters applied at different levels. This can lead to subtle bugs that are hard to track down.

Don’t Discard Filters: The Right Tool for the Right Job

This isn’t to say Filters are useless. They are a specialized tool designed for a specific purpose, and they excel at it.

You should always choose a Filter when your logic is tightly coupled to the MVC/API execution context. Ask yourself:

• Do I need to inspect or modify the action arguments? -> Use an Action Filter.
• Do I need to check ModelState.IsValid? -> Use an Action Filter.
• Do I need to conditionally apply logic to only a few action methods using attributes? -> Use a Filter.
• Do I need to manipulate the ActionResult before it’s converted to an HTTP response? -> Use a Result Filter.
• Do I need to handle exceptions that occur specifically during action execution or model binding? -> Use an Exception Filter.

Filters are the perfect tool for concerns that relate to the semantics of an action method, not the raw HTTP request.

A Quick Decision Guide

Conclusion

In the debate of Middleware vs. Filters, there’s no single winner, only the right choice for the context. However, for the broad, foundational, cross-cutting concerns that define an application’s behavior—logging, security, performance—Middleware is the robust, performant, and universal solution. It operates at the core of the request pipeline, providing maximum control and efficiency.

Reserve Filters for their intended purpose: as a powerful, specialized tool to hook into the MVC/API action-invocation lifecycle when you need access to that rich, high-level context. By understanding the fundamental difference in their scope and position in the pipeline, you can build cleaner, more performant, and more maintainable ASP.NET Core applications.