FnMCP.Nexus

An MCP (Model Context Protocol) server implementation in F# that exposes a context library as resources and provides tools and projections.

Overview

This MCP server provides access to a context library containing documentation about applications and frameworks. It implements the MCP protocol version 2024-11-05 and communicates via JSON-RPC over stdio.

Features

• Resources: Exposes markdown files from the context library as MCP resources
• Protocol: Standard MCP JSON-RPC over stdio
• Content Provider: File system-based content provider for documentation

Current Capabilities

• resources/list - Lists all available documentation resources
• resources/read - Reads specific resource content by URI
• tools/list - Placeholder for future tool implementations
• prompts/list - Placeholder for future prompt implementations

Building the Server

dotnet build src/FnMCP.Nexus/FnMCP.Nexus.fsproj

Running the Server

The server accepts an optional command-line argument for the context library path:

dotnet run --project src/FnMCP.Nexus [context-library-path]

If no path is provided, it defaults to context-library in the project root.

MCP Client Configuration

Claude Desktop / Junie

The server is configured in ~/.config/Claude/claude_desktop_config.json (Linux):

{
  "mcpServers": {
    "FnMCP.Nexus": {
      "command": "dotnet",
      "args": [
        "run",
        "--project",
        "/home/linux/RiderProjects/FnMCP.IvanTheGeek/src/FnMCP.Nexus"
      ],
      "env": {}
    }
  }
}

Note: After updating the configuration, restart Claude Desktop for changes to take effect.

Other MCP Clients

For other MCP-compatible clients, configure them to run:

• Command: dotnet
• Arguments: run --project <full-path-to-project>
• Communication: stdio (JSON-RPC)

Context Library Structure

The context library is organized as:

context-library/
├── apps/
│   └── laundrylog/
│       └── overview.md
└── framework/
    └── overview.md

Each markdown file becomes an MCP resource accessible via its URI path.

Development

Project Structure

• src/FnMCP.Nexus/ - Main source code
  • McpServer.fs - Core MCP server implementation
  • Program.fs - Entry point and JSON-RPC message loop
  • Types.fs - MCP protocol types
  • ContentProvider.fs - Content provider interface
  • FileSystemProvider.fs - File system-based provider
  • Resources.fs - Resource management
  • Tools.fs - Tool registry and handlers
  • Prompts.fs - Prompt registry and handlers

Requirements

• .NET 9.0 SDK
• F# compiler

Protocol Details

The server implements MCP protocol version 2024-11-05 using JSON-RPC 2.0:

• Input: JSON-RPC requests via stdin
• Output: JSON-RPC responses via stdout
• Logging: Diagnostic logs via stderr

Status

✅ Production Deployment Active

The server is deployed on VPS and accessible via HTTP/SSE transport:

• Endpoint: http://66.179.208.238:18080/sse
• Transport: SSE (Server-Sent Events) with Bearer token authentication
• Status: Operational since 2025-11-19

Resources and tools from the context library can be accessed through the MCP protocol.

Remote Access

HTTP/SSE Transport (Recommended)

The server supports remote access via HTTP with SSE transport:

Endpoints:

• Health: http://66.179.208.238:18080/
• SSE Events: http://66.179.208.238:18080/sse/events
• WebSocket: ws://66.179.208.238:18080/ws

Authentication: All endpoints (except health check) require Bearer token authentication. Generate an API key:

docker exec -i nexus-mcp ./FnMCP.Nexus /data/event-store generate-api-key \
  --scope full_access \
  --description "Your description"

Claude Desktop Configuration:

{
  "mcpServers": {
    "nexus-vps": {
      "url": "http://66.179.208.238:18080/sse",
      "transport": {
        "type": "sse",
        "headers": {
          "Authorization": "Bearer YOUR_API_KEY_HERE"
        }
      }
    }
  }
}

Local stdio Transport (Development)

For local development, you can also run the server in stdio mode:

./bin/local/FnMCP.Nexus /path/to/event-store