MCP TypeScript SDK

Table of Contents

• Overview
• Installation
• Quickstart
• What is MCP?
• Core Concepts
  • Server
  • Resources
  • Tools
  • Prompts
• Running Your Server
  • stdio
  • HTTP with SSE
  • Testing and Debugging
• Examples
  • Echo Server
  • SQLite Explorer
• Advanced Usage
  • Low-Level Server
  • Writing MCP Clients
  • Server Capabilities

Overview

The Model Context Protocol allows applications to provide context for LLMs in a standardized way, separating the concerns of providing context from the actual LLM interaction. This TypeScript SDK implements the full MCP specification, making it easy to:

• Build MCP clients that can connect to any MCP server
• Create MCP servers that expose resources, prompts and tools
• Use standard transports like stdio and SSE
• Handle all MCP protocol messages and lifecycle events

Installation

npm install @modelcontextprotocol/sdk

Quick Start

Let's create a simple MCP server that exposes a calculator tool and some data:

import { McpServer, ResourceTemplate } from "@modelcontextprotocol/sdk/server/mcp.js";
import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
import { z } from "zod";

// Create an MCP server
const server = new McpServer({
  name: "Demo",
  version: "1.0.0"
});

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

// Add a dynamic greeting resource
server.resource(
  "greeting",
  new ResourceTemplate("greeting://{name}", { list: undefined }),
  async (uri, { name }) => ({
    contents: [{
      uri: uri.href,
      text: `Hello, ${name}!`
    }]
  })
);

// Start receiving messages on stdin and sending messages on stdout
const transport = new StdioServerTransport();
await server.connect(transport);

What is MCP?

The Model Context Protocol (MCP) lets you build servers that expose data and functionality to LLM applications in a secure, standardized way. Think of it like a web API, but specifically designed for LLM interactions. MCP servers can:

• Expose data through Resources (think of these sort of like GET endpoints; they are used to load information into the LLM's context)
• Provide functionality through Tools (sort of like POST endpoints; they are used to execute code or otherwise produce a side effect)
• Define interaction patterns through Prompts (reusable templates for LLM interactions)
• And more!

Core Concepts

Server

The McpServer is your core interface to the MCP protocol. It handles connection management, protocol compliance, and message routing:

const server = new McpServer({
  name: "My App",
  version: "1.0.0"
});

Resources

Resources are how you expose data to LLMs. They're similar to GET endpoints in a REST API - they provide data but shouldn't perform significant computation or have side effects:

// Static resource
server.resource(
  "config",
  "config://app",
  async (uri) => ({
    contents: [{
      uri: uri.href,
      text: "App configuration here"
    }]
  })
);

// Dynamic resource with parameters
server.resource(
  "user-profile",
  new ResourceTemplate("users://{userId}/profile", { list: undefined }),
  async (uri, { userId }) => ({
    contents: [{
      uri: uri.href,
      text: `Profile data for user ${userId}`
    }]
  })
);

Tools

Tools let LLMs take actions through your server. Unlike resources, tools are expected to perform computation and have side effects:

// Simple tool with parameters
server.tool(
  "calculate-bmi",
  {
    weightKg: z.number(),
    heightM: z.number()
  },
  async ({ weightKg, heightM }) => ({
    content: [{
      type: "text",
      text: String(weightKg / (heightM * heightM))
    }]
  })
);

// Async tool with external API call
server.tool(
  "fetch-weather",
  { city: z.string() },
  async ({ city }) => {
    const response = await fetch(`https://api.weather.com/${city}`);
    const data = await response.text();
    return {
      content: [{ type: "text", text: data }]
    };
  }
);

Prompts

Prompts are reusable templates that help LLMs interact with your server effectively:

server.prompt(
  "review-code",
  { code: z.string() },
  ({ code }) => ({
    messages: [{
      role: "user",
      content: {
        type: "text",
        text: `Please review this code:\n\n${code}`
      }
    }]
  })
);

Running Your Server

MCP servers in TypeScript need to be connected to a transport to communicate with clients. How you start the server depends on the choice of transport:

stdio

For command-line tools and direct integrations:

import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";

const server = new McpServer({
  name: "example-server",
  version: "1.0.0"
});

// ... set up server resources, tools, and prompts ...

const transport = new StdioServerTransport();
await server.connect(transport);

HTTP with SSE

For remote servers, start a web server with a Server-Sent Events (SSE) endpoint, and a separate endpoint for the client to send its messages to:

import express, { Request, Response } from "express";
import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
import { SSEServerTransport } from "@modelcontextprotocol/sdk/server/sse.js";

const server = new McpServer({
  name: "example-server",
  version: "1.0.0"
});

// ... set up server resources, tools, and prompts ...

const app = express();

// to support multiple simultaneous connections we have a lookup object from
// sessionId to transport
const transports: {[sessionId: string]: SSEServerTransport} = {};

app.get("/sse", async (_: Request, res: Response) => {
  const transport = new SSEServerTransport('/messages', res);
  transports[transport.sessionId] = transport;
  res.on("close", () => {
    delete transports[transport.sessionId];
  });
  await server.connect(transport);
});

app.post("/messages", async (req: Request, res: Response) => {
  const sessionId = req.query.sessionId as string;
  const transport = transports[sessionId];
  if (transport) {
    await transport.handlePostMessage(req, res);
  } else {
    res.status(400).send('No transport found for sessionId');
  }
});

app.listen(3001);

Testing and Debugging

To test your server, you can use the MCP Inspector. See its README for more information.

Examples

Echo Server

A simple server demonstrating resources, tools, and prompts:

import { McpServer, ResourceTemplate } from "@modelcontextprotocol/sdk/server/mcp.js";
import { z } from "zod";

const server = new McpServer({
  name: "Echo",
  version: "1.0.0"
});

server.resource(
  "echo",
  new ResourceTemplate("echo://{message}", { list: undefined }),
  async (uri, { message }) => ({
    contents: [{
      uri: uri.href,
      text: `Resource echo: ${message}`
    }]
  })
);

server.tool(
  "echo",
  { message: z.string() },
  async ({ message }) => ({
    content: [{ type: "text", text: `Tool echo: ${message}` }]
  })
);

server.prompt(
  "echo",
  { message: z.string() },
  ({ message }) => ({
    messages: [{
      role: "user",
      content: {
        type: "text",
        text: `Please process this message: ${message}`
      }
    }]
  })
);

SQLite Explorer

A more complex example showing database integration:

import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
import sqlite3 from "sqlite3";
import { promisify } from "util";
import { z } from "zod";

const server = new McpServer({
  name: "SQLite Explorer",
  version: "1.0.0"
});

// Helper to create DB connection
const getDb = () => {
  const db = new sqlite3.Database("database.db");
  return {
    all: promisify<string, any[]>(db.all.bind(db)),
    close: promisify(db.close.bind(db))
  };
};

server.resource(
  "schema",
  "schema://main",
  async (uri) => {
    const db = getDb();
    try {
      const tables = await db.all(
        "SELECT sql FROM sqlite_master WHERE type='table'"
      );
      return {
        contents: [{
          uri: uri.href,
          text: tables.map((t: {sql: string}) => t.sql).join("\n")
        }]
      };
    } finally {
      await db.close();
    }
  }
);

server.tool(
  "query",
  { sql: z.string() },
  async ({ sql }) => {
    const db = getDb();
    try {
      const results = await db.all(sql);
      return {
        content: [{
          type: "text",
          text: JSON.stringify(results, null, 2)
        }]
      };
    } catch (err: unknown) {
      const error = err as Error;
      return {
        content: [{
          type: "text",
          text: `Error: ${error.message}`
        }],
        isError: true
      };
    } finally {
      await db.close();
    }
  }
);

Advanced Usage

Low-Level Server

For more control, you can use the low-level Server class directly:

import { Server } from "@modelcontextprotocol/sdk/server/index.js";
import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
import {
  ListPromptsRequestSchema,
  GetPromptRequestSchema
} from "@modelcontextprotocol/sdk/types.js";

const server = new Server(
  {
    name: "example-server",
    version: "1.0.0"
  },
  {
    capabilities: {
      prompts: {}
    }
  }
);

server.setRequestHandler(ListPromptsRequestSchema, async () => {
  return {
    prompts: [{
      name: "example-prompt",
      description: "An example prompt template",
      arguments: [{
        name: "arg1",
        description: "Example argument",
        required: true
      }]
    }]
  };
});

server.setRequestHandler(GetPromptRequestSchema, async (request) => {
  if (request.params.name !== "example-prompt") {
    throw new Error("Unknown prompt");
  }
  return {
    description: "Example prompt",
    messages: [{
      role: "user",
      content: {
        type: "text",
        text: "Example prompt text"
      }
    }]
  };
});

const transport = new StdioServerTransport();
await server.connect(transport);

Writing MCP Clients

The SDK provides a high-level client interface:

import { Client } from "@modelcontextprotocol/sdk/client/index.js";
import { StdioClientTransport } from "@modelcontextprotocol/sdk/client/stdio.js";

const transport = new StdioClientTransport({
  command: "node",
  args: ["server.js"]
});

const client = new Client(
  {
    name: "example-client",
    version: "1.0.0"
  },
  {
    capabilities: {
      prompts: {},
      resources: {},
      tools: {}
    }
  }
);

await client.connect(transport);

// List prompts
const prompts = await client.listPrompts();

// Get a prompt
const prompt = await client.getPrompt("example-prompt", {
  arg1: "value"
});

// List resources
const resources = await client.listResources();

// Read a resource
const resource = await client.readResource("file:///example.txt");

// Call a tool
const result = await client.callTool({
  name: "example-tool",
  arguments: {
    arg1: "value"
  }
});

Documentation

• Model Context Protocol documentation
• MCP Specification
• Example Servers

Contributing

Issues and pull requests are welcome on GitHub at https://github.com/modelcontextprotocol/typescript-sdk.

License

This project is licensed under the MIT License—see the LICENSE file for details.