🧠 serverless-mcp-server

A super simple Model Context Protocol (MCP) server deployed on AWS Lambda and exposed via Amazon API Gateway, deployed with Serverless Framework. This skeleton is based on the awesome work of Frédéric Barthelet: which has developed a middy middleware for Model Context Protocol (MCP) server integration with AWS Lambda functions in this repo

Long story

📖Read the full article here on dev.to

🛠 Features

• 🪄 Minimal MCP server setup using @modelcontextprotocol/sdk
• 🚀 Deployed as a single AWS Lambda function
• 🌐 HTTP POST endpoint exposed via API Gateway at /mcp
• 🔄 Supports local development via serverless-offline
• 🧪 Includes a simple example tool (add) with JSON-RPC interaction

📦 Project Structure

serverless-mcp-server/
├── src/                    # Source code
│   └── index.js                # MCP server handler
├── .gitignore              # Git ignore file
├── package.json            # Project dependencies
├── package-lock.json       # Project lock file
├── README.md               # This documentation file
└── serverless.yml          # Serverless Framework config

🛠 Prerequisites

• Node.js v22+
• Open Source Serverless or Serverless Framework v3+
• Serverless Offline

🚀 Getting Started

1. Install dependencies:

npm install

1. Install open source severless globally (if not already installed):

npm install -g osls

1. Run Locally with serverless-offline

npm sls offline

Local endpoint will be available at: POST http://localhost:3000/dev/mcp

Note that the /dev/ stage is added by default when using serverless-offline, reflecting Api Gateway V1 (REST API) behavior.

Switch to Api Gateway V2 (HTTP API)

If you want to use API Gateway V2, you can change the serverless.yml file to use httpApi instead of http in the events section. This will allow you to use HTTP APIs instead of REST APIs. This will allow you to use HTTP APIs instead of REST APIs.

functions:
  mcpServer:
    handler: src/index.handler
    events:
      - httpApi:
          path: mcp
          method: post

Local endpoint will be available at: POST http://localhost:3000/mcp

Note that the /dev/ stage is not needed when using API Gateway V2. Note you should change test curl and postman requests accordingly.

🧪 Test with MCP inspector

Run

npx @modelcontextprotocol/inspector node src/index.mjs

This will start the MCP inspector on port 6274. You can then open the inspector in your browser at http://127.0.0.1:6274. Configure parameters in the inspector:

• Select HTTP Streamable as Transport Type
• Set URL to http://localhost:3000/dev/mcp
• Click connect

You'll be able to see the list of tools and their parameters in the inspector.

🧪 Test with curl requests

List tools

curl --location 'http://localhost:3000/dev/mcp' \
--header 'content-type: application/json' \
--header 'accept: application/json' \
--header 'jsonrpc: 2.0' \
--data '{
  "jsonrpc": "2.0",
  "method": "tools/list",
  "id": 1
}'

➕ Use the add Tool

curl --location 'http://localhost:3000/dev/mcp' \
--header 'content-type: application/json' \
--header 'accept: application/json' \
--header 'jsonrpc: 2.0' \
--data '{
  "jsonrpc": "2.0",
  "id": 2,
  "method": "tools/call",
  "params": {
    "name": "add",
    "arguments": {
      "a": 5,
      "b": 3
    }
  }
}'

🧪 Test with jest

There are some basic tests included in the __tests__ folder. You can run them with:

npm run test

🧬 Code Breakdown

This code is based on the awesome work of Frédéric Barthelet: which has developed a middy middleware for Model Context Protocol (MCP) server integration with AWS Lambda functions in this repo

src/index.js

import middy from "@middy/core";
import httpErrorHandler from "@middy/http-error-handler";
import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
import { z } from "zod";
import mcpMiddleware from "middy-mcp";

const server = new McpServer({
  name: "Lambda hosted MCP Server",
  version: "1.0.0",
});

server.tool("add", { a: z.number(), b: z.number() }, async ({ a, b }) => ({
  content: [{ type: "text", text: String(a + b) }],
}));

export const handler = middy()
  .use(mcpMiddleware({ server }))
  .use(httpErrorHandler());

📡 Deploy to AWS

Just run:

sls deploy

After deployment, the MCP server will be live at the URL output by the command.

🔖 Quotes

This repository has been quoted in the following newsletters:

• Serverless Advocate Newsletter #33 by Lee Gilmore (AWS Hero)

📘 License

MIT — feel free to fork, tweak, and deploy your own version!