How do you build a custom MCP server for Claude?

TypeScript Implementation Example

Here is how you build a minimal custom MCP server in Node.js that exposes a custom calculator tool:

1. Initialize a project: npm init -y && npm install @modelcontextprotocol/sdk.
2. Write the server code (e.g. server.ts):

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

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

server.setRequestHandler(ListToolsRequestSchema, async () => ({
  tools: [{
    name: "calculate_cube",
    description: "Calculates the cube of a number.",
    inputSchema: {
      type: "object",
      properties: {
        number: { type: "number" }
      },
      required: ["number"]
    }
  }]
}));

server.setRequestHandler(CallToolRequestSchema, async (request) => {
  if (request.params.name === "calculate_cube") {
    const number = request.params.arguments?.number as number;
    return {
      content: [{ type: "text", text: String(number * number * number) }]
    };
  }
  throw new Error("Tool not found");
});

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