mcp-tool-proxy

mcp-proxy

A lightweight proxy that consolidates multiple MCP servers behind a single endpoint. Each child MCP server is exposed as one meta-tool — the agent sees N tools instead of hundreds, while retaining full access to every sub-tool.

The Problem

MCP clients like Claude Desktop, Antigravity, and others enforce a tool limit (commonly 100). A single MCP server like @digitalocean/mcp alone registers 190+ tools. Add Playwright, Serena, or any others and you quickly exceed the limit — making it impossible to use multiple MCP servers together.

The Solution

mcp-proxy sits between the agent and your MCP servers. It spawns each child MCP, discovers their tools, then exposes one meta-tool per server with tool_name and tool_input as parameters. The agent calls the meta-tool, and the proxy transparently routes the request to the correct child MCP.

Agent                 mcp-proxy              Child MCP Servers
──────                ─────────              ─────────────────
"playwright"  ──────►  route  ──────────────► @playwright/mcp       (23 tools)
"serena"      ──────►  route  ──────────────► serena                (28 tools)
"digitalocean"──────►  route  ──────────────► @digitalocean/mcp    (193 tools)

Agent sees: 3 tools                          Reality: 244 tools

Quick Start

1. Install

Via npx (no local clone needed):

npx mcp-tool-proxy

Or clone and install for local development:

git clone https://github.com/sevket/mcp-proxy.git
cd mcp-proxy
npm install

2. Configure your MCP servers

Copy the example config and add your MCP servers:

cp proxy-config.example.json proxy-config.json

Edit proxy-config.json with your actual MCP servers. The format is identical to Claude Desktop's claude_desktop_config.json:

{
  "mcpServers": {
    "playwright": {
      "command": "npx",
      "args": ["-y", "@playwright/mcp"],
      "env": {}
    },
    "digitalocean": {
      "command": "npx",
      "args": ["-y", "@digitalocean/mcp", "--services", "apps,droplets,databases"],
      "env": {
        "DIGITALOCEAN_API_TOKEN": "your_token_here"
      }
    }
  }
}

3. Point your MCP client to the proxy

Instead of registering each MCP server individually, register only the proxy. Here is an example for Claude Desktop (claude_desktop_config.json):

{
  "mcpServers": {
    "mcp-proxy": {
      "command": "npx",
      "args": ["-y", "mcp-tool-proxy"],
      "env": {}
    }
  }
}

(Or "command": "node", "args": ["/absolute/path/to/mcp-proxy/index.js"] for a local clone.)

Restart your MCP client — you should see one tool per child MCP server.

How It Works

1. Startup — The proxy reads proxy-config.json and spawns each child MCP server as a subprocess using stdio transport.
2. Discovery — It calls tools/list on each child to collect their available tools.
3. Meta-tool generation — For each child MCP, it creates a single meta-tool. The meta-tool's description lists all available sub-tools so the agent knows what's available. The tool_name parameter is an enum of all sub-tool names for precise routing.
4. Request routing — When the agent calls a meta-tool, the proxy extracts tool_name and tool_input, forwards the request to the correct child MCP, and returns the response as-is.

Meta-tool Schema

Each meta-tool accepts two parameters:

Parameter	Type	Description
tool_name	string	Name of the sub-tool to call (enum)
tool_input	object	Arguments to pass to the sub-tool

Adding a New MCP Server

Add a new entry to proxy-config.json:

{
  "mcpServers": {
    "existing-mcp": { "..." : "..." },
    "new-mcp": {
      "command": "npx",
      "args": ["-y", "@some/mcp-package"]
    }
  }
}

The proxy watches proxy-config.json and picks up changes live — no restart needed. The new server connects and appears as a meta-tool within a second or so of saving the file.

Troubleshooting

Issue	Solution
Child MCP fails to connect	Check the command path and env.PATH in proxy-config.json. Use absolute paths if needed.
Tool not found	Check proxy logs in stderr. Verify the tool exists in the child MCP.
Agent doesn't see updated tools	Config changes hot-reload automatically; if it still doesn't show up, check stderr for a "config reload failed" line (invalid JSON keeps the previous config running).
Partial startup	The proxy continues even if some children fail — check logs for errors.

Security Model

proxy-config.json entries are spawned directly (command + args, with env merged into the child's environment) — the proxy does not sandbox or validate what a command actually does. Treat this file like a shell script you'd run yourself: only put servers in it that you configured, and never point it at a proxy-config.json you downloaded or received from someone else without reading it first. There's no per-server permission model beyond toolAllowlist (which filters which tool names are reachable, not what those tools are allowed to do).

Requirements

• Node.js 18+
• npm

Contributing

See CONTRIBUTING.md.

License

MIT