MCP Middleware Adapter for Express Servers

@Moe03

Repository

Basic information

About MCP Middleware Adapter for Express Servers

Run multiple MCP clients on a NodeJS Express server (adapter/middleware)

#nodejs #adapter #middleware #express #mcp

MCP Middleware Adapter for Express Servers config

Add this server to your MCP-compatible client using the configuration below.

{
  "mcpServers": {
    "mcp-express-adapter": {
      "command": "npx",
      "args": [
        "mcp-express-adapter@latest",
        "--host",
        "http://localhost:3000/mcp/sse",
        "--header",
        "Authorization: Bearer 000000"
      ]
    }
  }
}

MCP Middleware Adapter for Express Servers tools

Tool list not available yet

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Fetch the live tool list by running this server in a temporary sandbox using the button above.

Overview

What is MCP Middleware Adapter for Express Servers?

It is a lightweight adapter that creates MCP (Model Context Protocol) servers using Express.js, allowing developers to host and serve MCP tools via SSE (Server-Sent Events) on an Express server. It targets developers who need to deploy, scale, and maintain multiple MCP clients efficiently.

How to use MCP Middleware Adapter for Express Servers?

Install via npm with npm install mcp-express-adapter@latest. Then define tools using the mcpTool helper with Zod schemas, create an MCPClient with an endpoint and tools, mount its middleware on an Express app, and connect to the SSE endpoint (e.g., http://localhost:3000/mcp/sse). To test with Claude Desktop, configure mcpServers using npx -y mcp-express-adapter --host <url>.

Key features of MCP Middleware Adapter for Express Servers

Express middleware integration with SSE transport
TypeScript‑friendly tool definition using Zod schemas
Header‑based authorization support
Multiple MCP clients on different endpoints
Lightweight design for deploying and scaling MCP servers
Simplifies hosting many MCP tools in one process

Use cases of MCP Middleware Adapter for Express Servers

Host weather, calculator, and time tools on separate Express endpoints
Combine lightweight MCP servers to avoid running many separate processes
Integrate MCP tools with LangChain agents via @langchain/mcp-adapters
Serve MCP tools to Claude Desktop or other MCP‑compatible clients
Scale MCP tools without spawning individual npx sessions for each user

Frequently asked questions

How do I install MCP Middleware Adapter for Express Servers?

Install it using npm, yarn, or pnpm: `npm install mcp-express-adapter@latest`. Note that if installing from a private GitHub Packages registry, you must authenticate.

Does it support WebSocket transport?

Currently only SSE (Server‑Sent Events) is implemented and working. WebSocket support is planned but not yet available.

Can I host multiple MCP clients on the same Express server?

Yes, you can create multiple `MCPClient` instances, each with a different endpoint (e.g., `/weather-mcp`, `/calculator-mcp`), and mount their middleware separately.

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