MCP server samples in JavaScript using the official MCP SDK — from a basic calculator with stdio transport to an advanced server with resources and event emitters.
@modelcontextprotocol/sdk package and Zod for schema validation. Both samples run with Node.js and use ES module syntax.
03-GettingStarted/samples/javascript, this is the simplest possible MCP server — four arithmetic tools over a stdio transport.Clone and navigate
git clone https://github.com/microsoft/mcp-for-beginners.git
cd mcp-for-beginners/03-GettingStarted/samples/javascript
{
"name": "tutorial-mcp",
"version": "1.0.0",
"type": "module",
"scripts": {
"start": "node index.js"
},
"dependencies": {
"@modelcontextprotocol/sdk": ">=1.26.0",
"zod": "^3.24.2"
}
}
import { McpServer } 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: "Calculator MCP Server",
version: "1.0.0"
});
// Add tool
server.tool(
"add",
{ a: z.number(), b: z.number() },
async ({ a, b }) => ({
content: [{ type: "text", text: String(a + b) }]
})
);
// Subtract tool
server.tool(
"subtract",
{ a: z.number(), b: z.number() },
async ({ a, b }) => ({
content: [{ type: "text", text: String(a - b) }]
})
);
// Multiply tool
server.tool(
"multiply",
{ a: z.number(), b: z.number() },
async ({ a, b }) => ({
content: [{ type: "text", text: String(a * b) }]
})
);
// Divide tool — includes divide-by-zero guard
server.tool(
"divide",
{ a: z.number(), b: z.number() },
async ({ a, b }) => {
if (b === 0) {
return {
content: [{ type: "text", text: "Error: Cannot divide by zero" }],
isError: true
};
}
return {
content: [{ type: "text", text: String(a / b) }]
};
}
);
// Connect via stdio
const transport = new StdioServerTransport();
server.connect(transport).catch(console.error);
console.log("Calculator MCP Server started");
04-PracticalImplementation/samples/javascript, this sample shows a class-based server architecture with a completion tool and a search resource.import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
import { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js';
import { z } from 'zod';
import EventEmitter from 'events';
class ExtendedMcpServer {
constructor(options = {}) {
this.serverName = options.serverName || 'JavaScript MCP Server';
this.models = options.models || ['gpt-4', 'llama-3-70b', 'claude-3-sonnet'];
this.events = new EventEmitter();
this.mcpServer = new McpServer({
name: this.serverName,
version: options.version || '1.0.0'
});
this.registerCompletionTool();
this.registerSearchResource();
}
async connect() {
const transport = new StdioServerTransport();
await this.mcpServer.connect(transport);
}
on(event, listener) {
this.events.on(event, listener);
}
}
| Pattern | Detail |
|---|---|
| Class-based server | Encapsulates server state and tool registration in a class |
| Event emitters | Emits request and completion events for monitoring/metrics |
| Resources with URI templates | search://{query} — clients read dynamic data via URI patterns |
| Model validation | Checks model name against a supported list before processing |