Calculator MCP Server

calculator-mcp is a small Streamable HTTP MCP (Model Context Protocol) server that exposes 16 arithmetic operations as callable tools for an AI LLM (Large Language Model) to consume. It contains no math of its own — every tool is a thin synchronous wrapper that logs its arguments and delegates to an open-source shared math calculator calculator-lib-rubens PyPI library package.

Features

16 calculator tools available via MCP:

Two-operand operations: add, subtract, multiply, divide, power, nth_root, modulo, floor_divide

Single-operand operations: sqrt, absolute, floor, ceil, log10, ln, exp

Rounding: round_number (with configurable decimal places)

AI Disclaimer

This project includes code and documentation created with the assistance of AI tools. For details on usage, limits, and review practices, please see the AI Disclaimer.

Prerequisites

• Python 3.14+
• pip 26.2+
• curl 8.7+

Installation and Usage

Installation

The calculator-mcp can be installed by running pip install calculator-mcp-rubens. It requires python 3.14+ and pip to run.

• To install locally into the user's home environment:

  # install "calculator-mcp" and depdencies into user local pip environment
  pip install --user calculator-mcp-rubens --verbose
  

Usage

Running the MCP Server

• Launch calculator-mcp locally with sensible defaults:

  # Launches the Streamable HTTP MCP server locally at:
  # http://0.0.0.0:9000/mcp
  # The "0.0.0.0" is used because this application is meant to run from
  # within a Docker container, which requires the wildcard address, or
  # INADDR_ANY, to accept HTTP connections from outside the container.
  calculator-mcp
  

Exercise the MCP Server Endpoints

1. Health check

   curl -v http://localhost:9000/health
   # Expect: OK
   

2. Initialize MCP session

The MCP endpoint requires a session, established via initialize first. Run these in order:

• a) Store JSON below in a local file /tmp/initialize.json:

  # remove indentation spaces when copying/pasting this command to the shell
  cat > /tmp/initialize.json <<EOF
  {
    "jsonrpc": "2.0",
    "id": 1,
    "method": "initialize",
    "params": {
      "protocolVersion": "2025-06-18",
      "capabilities": {},
      "clientInfo": {
        "name": "curl-test",
        "version": "1.0"
      }
    }
  }
  EOF
  

• b) MCP client initializes session — grab the Mcp-Session-Id from the response headers

  # Look for the "mcp-session-id: <SID>" header in the output
  curl -i http://localhost:9000/mcp \
  -H "Content-Type: application/json" \
  -H "Accept: application/json, text/event-stream" \
  -d @/tmp/initialize.json
  

• c) MCP client sends the required "initialized" notification (use the SID from step b)

  SID="<paste-mcp-session-id-here>"
  # Expect "202 Accepted" response
  curl -v http://localhost:9000/mcp \
  -H "Content-Type: application/json" \
  -H "Accept: application/json, text/event-stream" \
  -H "Mcp-Session-Id: $SID" \
  -d '{"jsonrpc":"2.0","method":"notifications/initialized"}'
  

3. List tools

• Once you have initialized your MCP session, list all the tools:

  curl -s http://localhost:9000/mcp \
  -H "Content-Type: application/json" \
  -H "Accept: application/json, text/event-stream" \
  -H "Mcp-Session-Id: $SID" \
  -d '{"jsonrpc":"2.0","id":2,"method":"tools/list"}'
  

This returns all 16 tools: add, subtract, multiply, divide, power, nth_root, modulo, floor_divide, sqrt, absolute, floor, ceil, log10, ln, exp, round_number.

4. Call a tool (e.g. add)

• To call one of the tools (e.g., add)

  curl -s http://localhost:9000/mcp \
    -H "Content-Type: application/json" \
    -H "Accept: application/json, text/event-stream" \
    -H "Mcp-Session-Id: $SID" \
    -d '{"jsonrpc":"2.0","id":3,"method":"tools/call","params":{"name":"add","arguments":{"a":2,"b":3}}}'
  

Returns {"result": 5.0} in structuredContent. Swap name and arguments to call any other tool, e.g. {"name": "divide", "arguments": {"a": 15, "b": 4}} or {"name": "sqrt", "arguments": {"a": 16}}.

Note: the same Mcp-Session-Id must be reused across steps b, c, 3, and 4 — the server ties the session to that ID.

Configuration

The server ships with a default config.yaml bundled inside the package. To override it, set the CALCULATOR_MCP_CONFIG environment variable to the absolute path of your custom configuration file:

export CALCULATOR_MCP_CONFIG=/path/to/your/config.yaml

When CALCULATOR_MCP_CONFIG is not set, the bundled default is used automatically.

The configuration file has three sections. The logging section controls Python logging via dictConfig. The default configuration logs calculator_mcp messages at DEBUG level to stderr.

# =============================================================================
# Server Configuration
# =============================================================================
server:
    # the home page of this project
    homepage: "https://github.com/rubensgomes-org/calculator-mcp"
    # MCP transport: "stdio" or "http"
    # http: for web services using the Streamable HTTP protocol
    transport: "http"
    # Host IP address for the HTTP/MCP server.
    # 0.0.0.0 binds all interfaces, which is required inside a container.
    # Use 127.0.0.1 to restrict the server to localhost only.
    host: "0.0.0.0"
    # Port for the HTTP/MCP server.
    port: 9000
    # timeout in seconds
    timeout: 10

# =============================================================================
# Client Configuration
# =============================================================================
client:
    # the URL the client should use when the server transport is "http"
    #    is_oauth: false
    #    url: "http://127.0.0.1:9000/mcp"
    is_oauth: true
    url: "https://rubens-calculator-mcp.fastmcp.app/mcp"
    # location to store OAuth token
    token_dir: "~/.fastmcp"
    # fixed port for the OAuth callback server
    callback_port: 10000

# =============================================================================
# Logging Configuration
# =============================================================================
logging:
    version: 1
    disable_existing_loggers: false
    formatters:
        standard:
            format: "%(asctime)s [%(levelname)s] %(name)s: %(message)s"
    handlers:
        console:
            class: logging.StreamHandler
            formatter: standard
            stream: ext://sys.stderr
    loggers:
        calculator_mcp:
            level: DEBUG
            handlers:
                - console
            propagate: false
        # MCP protocol tracing — set to DEBUG to see full JSON-RPC messages
        mcp.client.streamable_http:
            level: INFO
            handlers:
                - console
            propagate: false
        # HTTP request/response summaries — set to DEBUG for detail
        httpx:
            level: DEBUG
            handlers:
                - console
            propagate: false
        # HTTP wire-level tracing (headers, TCP) — set to DEBUG for detail
        httpcore:
            level: INFO
            handlers:
                - console
            propagate: false
        # Server: inbound JSON-RPC messages — set to DEBUG to see parsed requests
        mcp.server.lowlevel.server:
            level: INFO
            handlers:
                - console
            propagate: false
        # Server: StreamableHTTP transport — set to DEBUG for method-level tracing
        mcp.server.streamable_http:
            level: INFO
            handlers:
                - console
            propagate: false
        # Server: session/transport lifecycle — set to DEBUG for session details
        mcp.server.streamable_http_manager:
            level: INFO
            handlers:
                - console
            propagate: false
        # Server: HTTP request lines (method, path, status)
        uvicorn.access:
            level: INFO
            handlers:
                - console
            propagate: false
    root:
        level: WARNING
        handlers:
            - console

License

The project is licensed under MIT License.

Author: Rubens Gomes