Filters

What Is a Filter?

IEndpointFilter is an interface provided by ASP.NET Core Minimal APIs. It lets you run logic before and after a request reaches the handler.

How It Differs from Middleware

Middleware is applied globally to all requests, while filters can be scoped to specific endpoints or groups. This lets you apply cross-cutting concerns such as audit logging, validation, or rate limiting only where they are needed.

Registering Filters in AxisEndpoints

In AxisEndpoints, register filters with config.AddFilter<TFilter>(). Filters are resolved from the DI container, so constructor injection works as expected.

Filter classes defined in the assembly or assemblies passed to AddAxisEndpoints() — by default, the entry assembly — are registered automatically by its scanning, so manual registration is not required for those. This does not extend to filters shipped in a separate NuGet package, since that package’s assembly is not scanned unless you pass it explicitly. Such packages must register their filters themselves; the CSV Helper extension does this via AddAxisEndpointsCsvHelper(). See the CSV Helper extension for an example.

---

Implement IEndpointFilter and register it with config.AddFilter<TFilter>(). Filters are resolved from DI per request, so constructor injection is supported. Registering a filter on a group applies it to all endpoints in that group.

public class LoggingFilter : IEndpointFilter
{
    private readonly ILogger<LoggingFilter> _logger;

    public LoggingFilter(ILogger<LoggingFilter> logger) => _logger = logger;

    public async ValueTask<object?> InvokeAsync(
        EndpointFilterInvocationContext context,
        EndpointFilterDelegate next)
    {
        _logger.LogInformation("{Method} {Path}",
            context.HttpContext.Request.Method,
            context.HttpContext.Request.Path);

        var result = await next(context);

        _logger.LogInformation("Response: {StatusCode}",
            context.HttpContext.Response.StatusCode);

        return result;
    }
}

Per-endpoint

public class MyEndpoint : IEndpoint<MyRequest, Response<MyResponse>>
{
    public void Configure(IEndpointConfiguration config)
    {
        config.Post("/items").AddFilter<LoggingFilter>();
    }
    // ...
}

Group-level

Filters applied to a group affect all endpoints in that group:

public class MyGroup : IEndpointGroup
{
    public void Configure(IEndpointGroupConfiguration config)
    {
        config.Prefix("/api/items").AddFilter<LoggingFilter>();
    }
}

Difference from middleware

IEndpointFilter differs from middleware in that it can be scoped to individual endpoints or groups, rather than applying globally to all requests.

For a FluentValidation example using IEndpointFilter, see the Validation guide. For grouping endpoints, see the Endpoint Groups guide.