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How to build an MCP server - Calculator Example

How to build an MCP server - Calculator Example

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github.com/simonbernerDeveloper Tools1Updated 80w ago
Repository

About How to build an MCP server - Calculator Example

A Python example MCP server that provides basic math operations. It is intended for developers learning to build, test, and integrate a simple server with MCP clients.

Key features

  1. 01Basic math operations
  2. 02Python-based MCP server example
  3. 03Local testing with MCP Inspector
  4. 04Pytest-based tests

Use cases

  1. 01Learning MCP server development
  2. 02Testing a calculator server locally
  3. 03Integrating math tools with an MCP client

MCP support

Exposes basic math operations as tools for MCP clients. The project also documents local testing and client configuration.

Configuration

Local server config is the same for every client. Copy it into your client’s MCP config file.

mcp.json · Universal config
{
  "mcpServers": {
    "calculator-simonberner": {
      "command": "npx",
      "args": [
        "-y",
        "@smithery/cli"
      ]
    }
  }
}
Run commandnpx -y @smithery/cli

Local servers need a runtime on your machine (e.g. Node.js 18+). Config file locations differ by client; see your client’s docs.

Packages
npm@smithery/cli

Tools

No tool list yet

Local servers expose tools only once running on your machine, and the maintainer has not provided a tool list.

Details

From the project README

How to build an MCP server - Calculator Example

smithery badge License: MIT

About

This is a very simple example of how to build an MCP server that provides basic math operations to an MCP client.

What is MCP?

Model Context Protocol (MCP) is a protocol that enables LLMs to access custom tools and services. An MCP client can make requests to MCP servers to access tools that they provide. This example represents a simple calculator server that provides basic math operations to a client.

"MCP can provide a single, standardized way for AI models to interact with external systems. You write code once and all AI systems can use it." 1

"Servers are the fundamental building block that enriches LLMs with external data and context." 2

Chat MCP Calculator

Tech Stack

  • Python3
  • Pytest
  • MCP SDK
  • MCP CLI
  • Nix (optional)

How to setup and use

Smithery

To install mcp-server-calculator for Claude Desktop automatically via Smithery:

npx -y @smithery/cli install @simonberner/mcp-server-calculator --client claude
Development Setup

As we are using Nix in this project for having a reproducible and isolated development environment, there is no need to install Python or any other dependencies. You will get everything you need out of the box. Also there is no need to create a virtual environment in Python using venv or poetry, but you have to be willing to install Nix on your system.

  • Install direnv (used to load the development environment)
  • Install Lix
  • Clone this repository
  • cd into the directory
  • Run direnv allow
  • Run pytest
Alternative

If you don't want to take the Smithery or the Nix route, you can of course also use uv to build the package/project. Here is some guidance:

# Install uv (see https://docs.astral.sh/uv/getting-started/installation/)
curl -LsSf https://astral.sh/uv/install.sh | sh

# Create a virtual environment named .venv
uv venv

# Activate the virtual environment (example for bash/zsh)
source .venv/bin/activate

# Now run the install or build commands
uv pip install -e .
# or
uv pip wheel . -w dist
Running & Testing the Server locally
mcp dev src/mcp_server_calculator/calculator.py
Host/Client integration
  • Add the following to your mcp config:
{
  "mcpServers": {
    "calculator": {
      "command": "python",
      "args": [
        "<YOUR-PATH>/mcp-server-calculator/src/mcp_server_calculator/calculator.py"
      ]
    }
  }
}
Notes
  • When using Windsurf IDE as MCP Host, you need to have a Pro Plan to be able to use Cascade (as MCP Client) with MCP Servers.

Issues

Check Issues for seeing the current issues or for opening a new one.

Resources

Credits

Nice things to know

Nix
Cloudflare

Comments

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New to MCP?

From what the protocol is to installing your first server, these answers cover most first questions.

An open protocol that defines how AI applications connect to external tools and data in a uniform way. Clients talk to the model; MCP servers provide tools, resources and prompt templates. They exchange standard messages, so one server can be reused by many clients.