CognitiveForge.McpCategoryRouting

Category-based routing for .NET MCP servers. Expose different subsets of tools, prompts, and resources on different URL paths from a single MCP server.

Overview

This library hooks into the Model Context Protocol (MCP) SDK for .NET and filters MCP primitives per HTTP session based on a route parameter. For example, app.MapMcp("/{category}") lets requests to /analytics see only analytics tools while /ops sees only operations tools.

Filtering happens at session connection time via IPostConfigureOptions<HttpServerTransportOptions>, so there is no per-message overhead.

Prerequisites

• .NET 10 SDK or later

Installation

dotnet add package CognitiveForge.McpCategoryRouting

Quick Start

using CognitiveForge.McpCategoryRouting;
using ModelContextProtocol.Server;
using System.ComponentModel;

var builder = WebApplication.CreateBuilder(args);

builder.Services
    .AddMcpServer()
    .WithHttpTransport()
    .WithToolsFromAssembly(typeof(Program).Assembly)
    .AddCategoryFilters(); // enable category filtering

var app = builder.Build();
app.MapMcp("/{category}"); // standard MapMcp with a route parameter
app.Run();

// Tools categorized as "analytics" — visible at /analytics
[McpServerToolType]
[McpCategory("analytics")]
public static class AnalyticsTools
{
    [McpServerTool, Description("Returns a tiny analytics summary.")]
    public static string GetSummary() => "Users: 42, ConversionRate: 3.1%";
}

// Tools categorized as "ops" — visible at /ops
[McpServerToolType]
[McpCategory("ops")]
public static class OperationsTools
{
    [McpServerTool, Description("Returns a simple health status.")]
    public static string GetHealth() => "OK";
}

See the samples/Basic project for a complete working example.

Configuration

Pass an options delegate to AddCategoryFilters():

.AddCategoryFilters(options =>
{
    options.RouteValueName = "category";
    options.CaseInsensitive = true;
    options.UncategorizedBehavior = UncategorizedBehavior.ExcludeAlways;
});

Property	Default	Description
RouteValueName	"category"	ASP.NET Core route parameter name to read
CaseInsensitive	true	Case-insensitive category matching
DisableFilteringWhenCategoryMissing	true	Skip filtering when the route has no category segment (expose all primitives)
UncategorizedBehavior	ExcludeAlways	How to handle primitives with no category (see below)
FallbackCategory	"mcp"	Route value that activates uncategorized primitives when using FallbackRoute behavior

Category Assignment

Apply [McpCategory] to a class (affects all tools in the class) or to individual methods:

[McpCategory("analytics")]
[McpCategory("reporting")] // multiple categories allowed
public static class MultiCategoryTools { ... }

[System.ComponentModel.Category] is also supported as a fallback when [McpCategory] is not present.

Uncategorized Primitives

The UncategorizedBehavior enum controls visibility of primitives that have no category:

Value	Behavior
IncludeAlways	Always visible on every route
ExcludeAlways	Never visible (default)
FallbackRoute	Visible only when the route matches FallbackCategory

Building

dotnet build CognitiveForge.McpCategoryRouting.slnx

Testing

# Run all tests
dotnet test CognitiveForge.McpCategoryRouting.slnx

# Run unit tests only
dotnet test src/CognitiveForge.McpCategoryRouting.Tests

# Run integration tests only
dotnet test src/CognitiveForge.McpCategoryRouting.IntegrationTests

# Run a single test
dotnet test src/CognitiveForge.McpCategoryRouting.Tests --filter "FullyQualifiedName~GetCategories_should_return_empty"

Contributing

Contributions are welcome! Please open an issue or submit a pull request.

License

This project is licensed under the MIT License.