How to Build a Custom MCP Server in TypeScript & Python: A Complete 2026 Developer Tutorial

import { Server } from "@modelcontextprotocol/sdk/server/index.js";
import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
import {
  CallToolRequestSchema,
  ListToolsRequestSchema,
} from "@modelcontextprotocol/sdk/types.js";
import { z } from "zod";

const server = new Server(
  { name: "metrics-mcp-server", version: "1.0.0" },
  { capabilities: { tools: {} } }
);

// 1. Define available tools
server.setRequestHandler(ListToolsRequestSchema, async () => {
  return {
    tools: [
      {
        name: "get_active_users",
        description: "Returns the current active users count for a given region",
        inputSchema: {
          type: "object",
          properties: {
            region: { type: "string", description: "e.g. us-east, eu-west" }
          },
          required: ["region"]
        }
      }
    ]
  };
});

// 2. Handle tool invocation
server.setRequestHandler(CallToolRequestSchema, async (request) => {
  if (request.params.name === "get_active_users") {
    const region = String(request.params.arguments?.region ?? "us-east");
    const count = Math.floor(Math.random() * 5000) + 1200; // Replace with live API/DB call
    return {
      content: [
        {
          type: "text",
          text: "Active users in " + region + ": " + count
        }
      ]
    };
  }
  throw new Error("Tool not found");
});

// 3. Connect via Standard Input/Output
async function main() {
  const transport = new StdioServerTransport();
  await server.connect(transport);
  console.error("Metrics MCP Server running on stdio");
}
main();

from mcp.server.fastmcp import FastMCP

# Initialize FastMCP Server
mcp = FastMCP("DevOps Server")

@mcp.tool()
def restart_service(service_name: str, environment: str = "staging") -> str:
    """Restarts a backend microservice in the designated environment."""
    # Place your live Docker / Kubernetes / AWS call here
    return f"Successfully restarted {service_name} in {environment} cluster."

if __name__ == "__main__":
    mcp.run()

{
  "mcpServers": {
    "my-custom-metrics": {
      "command": "node",
      "args": ["/absolute/path/to/custom-mcp-server/dist/index.js"]
    }
  }
}