Plugin System

dotnet-mcp-server has a drop-in plugin system. You can add your own tools to the server without forking or modifying the core project.

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How It Works

1. You write a .NET class library that implements the ITool interface
2. You build it to a DLL
3. You copy the DLL into the plugins/ directory
4. The server discovers and loads it automatically on the next start

The server scans for DLLs in the plugins/ folder at startup, instantiates any class implementing ITool, and registers them alongside the built-in tools. Your plugin tool appears in tools/list exactly like a built-in.

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Plugin vs. Built-in Tool

	Built-in tool	Plugin tool
Where code lives	src/McpServer/Tools/	Your own repository
How to install	Always included	Copy DLL to plugins/
Requires server fork	No (it's in the server)	No
Requires server restart	N/A	Yes, once after installing
Config access	Via IOptions<T>	Via PluginContext.GetConfig()

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Plugin Directory Location

Install method	Plugins directory
Global tool (Windows)	%APPDATA%\dotnet-mcp-server\plugins\
Global tool (Linux/macOS)	~/.config/dotnet-mcp-server/plugins\
Clone & build	plugins\ next to appsettings.json

You can override the directory via appsettings.json:

{
  "Plugins": {
    "Directory": "C:\\MyCustomPlugins"
  }
}

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Getting Started

The fastest way to write a plugin is with the project template:

dotnet new install DotnetMcpServer.Templates
dotnet new mcp-tool -n MyTool

Full Plugin Quickstart →

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Plugin Configuration

Pass values to your plugin via the Plugins.Config section in appsettings.json:

{
  "Plugins": {
    "Config": {
      "api_base_url": "https://api.example.com",
      "api_key": "your-key-here"
    }
  }
}

Read them in your plugin using the PluginContext constructor:

public class MyTool : ITool
{
    private readonly string _apiBaseUrl;

    public MyTool(PluginContext context)
    {
        _apiBaseUrl = context.GetConfig("api_base_url") ?? "https://default.example.com";
    }
}

API Reference →