MCP Local Router

This project is an MCP (Model Context Protocol) local router that serves as an aggregation proxy for MCP servers. It can connect to multiple upstream MCP servers and aggregate their functionalities into a single interface for downstream clients.

Features

- Supports specifying a configuration file via command line arguments
- Supports configuring multiple upstream MCP servers
- Supports stdio transport
- Supports injecting environment variables into stdio transport
- Supports SSE transport with aggregated /sse and per-upstream /sse/{serverName} endpoints

Usage

Running

It must be run with a configuration file:

cargo run -- --config mcp-config.json --transport sse

SSE Routing

When the router runs with --transport sse, it exposes two kinds of endpoints:

- /sse streams the aggregated tool surface area from every configured upstream server.
- /sse/{serverName} streams only the tools from a single upstream. The {serverName} segment must match the key from mcpServers in your configuration file (for example /sse/filesystem or /sse/workspace-search).

The server name keys should be URL-safe because they are used directly as path segments.

Each SSE connection emits an initial endpoint event containing the HTTP path clients should use for POST requests. All streaming endpoints share the same POST /message?sessionId=… channel.

Configuration File Format

The configuration file is in JSON format; an example is shown below:

{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": [
        "-y",
        "@modelcontextprotocol/server-filesystem",
        "/Users/username/Desktop"
      ],
      "env": {
        "LINEAR_ACCESS_TOKEN": "your_personal_access_token"
      }
    },
    "workspace-search": {
      "command": "npx",
      "args": [
        "-y",
        "@modelcontextprotocol/server-everything"
      ],
      "env": {}
    }
  }
}

Description:

- mcpServers: a mapping of multiple server configurations
- Each key is the server's name (used for logging and the /sse/{serverName} path)
- Each value is an object containing the following fields:
- command: the command to execute
- args: an array of command arguments
- env: a mapping of environment variables to inject

Build and Installation

```bash