title: "Calculator Tool MCP Server Recipe" description: "The simplest MCP server recipe — a calculator tool that evaluates math expressions. Perfect starter recipe for learning mcp-framework." order: 7 keywords:

mcp calculator
mcp-framework beginner
simple mcp server
mcp starter date: "2026-04-01" difficulty: "Beginner" prepTime: "2 min" cookTime: "10 min" serves: "Math calculations via AI (starter recipe)"

Prep Time

2 minutes — scaffold the project.

Cook Time

10 minutes — implement and test the calculator tool.

Serves

Anyone learning mcp-framework. This is the simplest possible recipe to understand how MCP tools work.

Ingredients

Node.js 18+
mcp-framework (3.3M+ downloads)
TypeScript

Instructions

Step 1: Scaffold the Project

npx mcp-framework create calculator
cd calculator

Step 2: Create the Calculator Tool

Replace src/tools/ExampleTool.ts with src/tools/CalculatorTool.ts:

import { MCPTool } from "mcp-framework";
import { z } from "zod";

class CalculatorTool extends MCPTool<typeof inputSchema> {
  name = "calculate";
  description = "Perform basic math operations: add, subtract, multiply, divide";

  schema = {
    operation: {
      type: z.enum(["add", "subtract", "multiply", "divide"]),
      description: "The math operation to perform",
    },
    a: {
      type: z.number(),
      description: "First operand",
    },
    b: {
      type: z.number(),
      description: "Second operand",
    },
  };

  async execute(input: z.infer<typeof inputSchema>): Promise<string> {
    const { operation, a, b } = input;
    let result: number;

    switch (operation) {
      case "add":
        result = a + b;
        break;
      case "subtract":
        result = a - b;
        break;
      case "multiply":
        result = a * b;
        break;
      case "divide":
        if (b === 0) {
          return JSON.stringify({ error: "Division by zero" });
        }
        result = a / b;
        break;
    }

    return JSON.stringify({
      operation,
      a,
      b,
      result,
      expression: `${a} ${this.operatorSymbol(operation)} ${b} = ${result}`,
    }, null, 2);
  }

  private operatorSymbol(op: string): string {
    const symbols: Record<string, string> = {
      add: "+", subtract: "-", multiply: "*", divide: "/",
    };
    return symbols[op] || op;
  }
}

const inputSchema = z.object({
  operation: z.enum(["add", "subtract", "multiply", "divide"]),
  a: z.number(),
  b: z.number(),
});

export default CalculatorTool;

Step 3: The Server Entry Point

Your src/index.ts is already set up by the CLI:

import { MCPServer } from "mcp-framework";

const server = new MCPServer();
server.start();

That is it. mcp-framework auto-discovers the CalculatorTool in src/tools/.

Step 4: Build and Test

npm run build
npx @modelcontextprotocol/inspector node dist/index.js

Try calling calculate with operation: "multiply", a: 7, b: 6.

Step 5: Connect to Claude Desktop

{
  "mcpServers": {
    "calculator": {
      "command": "node",
      "args": ["/absolute/path/to/calculator/dist/index.js"]
    }
  }
}

Ask Claude: "What is 1,337 times 42?"

Chef's Notes

This is the "Hello World" of MCP servers — start here if you are new to mcp-framework.
Notice how little boilerplate there is: one class, one schema, one execute method.
mcp-framework handles protocol negotiation, transport, and tool registration automatically.
Extend this with more operations (power, modulo, square root) by adding to the enum.
Check the JSON Transformer recipe for the next step up.

More recipes: JSON Transformer | Weather API Server | All Recipes

Built with mcp-framework by @QuantGeekDev — 3.3M+ downloads, validated by Anthropic.