# MCP To LangChain Tools Conversion Utility / TypeScript [![License: MIT](https://img.shields.io/badge/License-MIT-blue.svg)](https://github.com/hideya/langchain-mcp-tools-ts/blob/main/LICENSE) [![npm version](https://img.shields.io/npm/v/@h1deya/langchain-mcp-tools.svg)](https://www.npmjs.com/package/@h1deya/langchain-mcp-tools)

This package is intended to simplify the use of
[Model Context Protocol (MCP)](https://modelcontextprotocol.io/)
server tools with LangChain / TypeScript.

[Model Context Protocol (MCP)](https://modelcontextprotocol.io/),
an open source technology
[announced by Anthropic](https://www.anthropic.com/news/model-context-protocol),
dramatically expands LLM’s scope
by enabling external tool and resource integration, including
Google Drive, Slack, Notion, Spotify, Docker, PostgreSQL, and more…

Over 2000 functional components available as MCP servers:

- [MCP Server Listing on the Official Site](https://github.com/modelcontextprotocol/servers?tab=readme-ov-file#model-context-protocol-servers)
- [MCP.so - Find Awesome MCP Servers and Clients](https://mcp.so/)
- [Smithery: MCP Server Registry](https://smithery.ai/)

The goal of this utility is to make these 2000+ MCP servers readily accessible from LangChain.

It contains a utility function `convertMcpToLangchainTools()`.  
This async function handles parallel initialization of specified multiple MCP servers
and converts their available tools into an array of LangChain-compatible tools.

For detailed information on how to use this library, please refer to the following document:
- ["Supercharging LangChain: Integrating 2000+ MCP with ReAct"](https://medium.com/@h1deya/supercharging-langchain-integrating-450-mcp-with-react-d4e467cbf41a)

A python equivalent of this utility is available
[here](https://pypi.org/project/langchain-mcp-tools)

## Prerequisites

- Node.js 16+

## Installation

```bash
npm i @h1deya/langchain-mcp-tools
```

## Quick Start

`convertMcpToLangchainTools()` utility function accepts MCP server configurations
that follow the same structure as
[Claude for Desktop](https://modelcontextprotocol.io/quickstart/user),
but only the contents of the `mcpServers` property,
and is expressed as a JS Object, e.g.:

```ts
const mcpServers: McpServersConfig = {
  filesystem: {
    command: "npx",
    args: ["-y", "@modelcontextprotocol/server-filesystem", "."]
  },
  fetch: {
    command: "uvx",
    args: ["mcp-server-fetch"]
  }
};

const { tools, cleanup } = await convertMcpToLangchainTools(mcpServers);
```

This utility function initializes all specified MCP servers in parallel,
and returns LangChain Tools
([`tools: StructuredTool[]`](https://api.js.langchain.com/classes/_langchain_core.tools.StructuredTool.html))
by gathering available MCP tools from the servers,
and by wrapping them into LangChain tools.
It also returns an async callback function (`cleanup: McpServerCleanupFn`)
to be invoked to close all MCP server sessions when finished.

The returned tools can be used with LangChain, e.g.:

```ts
// import { ChatAnthropic } from "@langchain/anthropic";
const llm = new ChatAnthropic({ model: "claude-3-7-sonnet-latest" });

// import { createReactAgent } from "@langchain/langgraph/prebuilt";
const agent = createReactAgent({
  llm,
  tools
});
```

Find complete, minimal working usage examples
[here](https://github.com/hideya/langchain-mcp-tools-ts-usage/blob/main/src/index.ts)

For hands-on experimentation with MCP server integration,
try [this LangChain application built with the utility](https://github.com/hideya/mcp-client-langchain-ts)

For detailed information on how to use this library, please refer to the following document:  
["Supercharging LangChain: Integrating 2000+ MCP with ReAct"](https://medium.com/@h1deya/supercharging-langchain-integrating-450-mcp-with-react-d4e467cbf41a)

## Experimental Features

### Remote MCP Server Support

`mcp_servers` configuration for SSE and Websocket servers are as follows:

```ts
    "sse-server-name": {
        url: `http://${sse_server_host}:${sse_server_port}/...`
    },

    "ws-server-name": {
        url: `ws://${ws_server_host}:${ws_server_port}/...`
    },
```

Note that the key `"url"` may be changed in the future to match
the MCP server configurations used by Claude for Desktop once
it introduces remote server support.

### Working Directory Configuration for Local MCP Servers

The working directory that is used when spawning a local MCP server
can be specified with the `"cwd"` key as follows:

```ts
    "local-server-name": {
      command: "...",
      args: [...],
      cwd: "/working/directory"  // the working dir to be use by the server
    },
```

### Configuration for MCP Server stderr Redirection

A new key `"stderr"` has been introduced to specify a file descriptor
to which MCP server's stderr is redirected.

```ts
    const logPath = `mcp-server-${serverName}.log`;
    const logFd = fs.openSync(logPath, "w");
    mcpServers[serverName].stderr = logFd;
```

The key `stderr` is derived from TypeScript SDK's `StdioServerParameters`.

## Limitations

- Currently, only text results of tool calls are supported.
- Fatures other than [Tools](https://modelcontextprotocol.io/docs/concepts/tools) are not supported.

## Change Log

Can be found [here](https://github.com/hideya/langchain-mcp-tools-ts/blob/main/CHANGELOG.md)