Model Context Protocol

CalculatorLib MCP server

Exact answers from thousands of calculators and 67 unit converters, right inside Claude, ChatGPT, Cursor and any MCP client.

  • Free
  • No signup
  • Streamable HTTP
Server URL https://calculatorlib.com/mcp
Connect a client Try it live

Connect in under a minute

Pick your client and follow the steps.

  1. Open Settings → Connectors (claude.ai or Claude Desktop).
  2. Click Add custom connector, name it CalculatorLib and paste the server URL.
  3. Start a new chat and ask a question that needs a calculation.

Tools

Search first, then run: your agent loads 5 small tools instead of thousands.

search_calculators

Find calculators by keyword, in any of 12 languages.

{"query": "mortgage"}

run_calculator

Run a calculator: the result, the formula with your values and a share link.

{"name": "bmi_calculator", "args": {…}}

get_calculator_schema

Get every input field of one calculator. Optional.

{"name": "bmi_calculator"}

convert_units

One tool for 67 unit categories: length, mass, temperature, data and more. The former convert_<category> tools still answer but are no longer listed.

{"value": 5, "from": "Meter", "to": "Foot"}

solve_math

Solve equations, derivatives, integrals, limits and trigonometry step by step; every answer is checked numerically.

{"problem": "x^2-5x+6=0"}

    What a call returns

    1. You ask

      “What’s my BMI at 70 kg and 170 cm?”

    2. The agent calls 
      run_calculator({
  "name": "bmi_calculator",
  "args": {
    "unitSystem": "metric",
    "weight": 70,
    "height": 170
  }
})
    3. The server returns

      BMI 24.2 · Normal weight (WHO)

      Formula
      BMI = 70 / (170/100)² = 24.2
      Link
      /bmi-calculator?weight=70&height=170

      Plus structuredContent JSON with every value and label.

    Try it live

    Real requests to /mcp, sent from your browser.

    Token (optional)
    Raw JSON-RPC
    Request
    Response

    Limits and authentication

    No key needed. A token gives you a higher limit and your own call log.

    Access Rate limit Monthly calls Call log
    Anonymous 60 / min per IP No cap No
    With a token 600 / min By plan · Free: 2,000 Yes

    Over the limit you get HTTP 429 with Retry-After: 60.

    Use a token

    1. Create a token (sign-in required). It starts with clk_ and is shown only once.
    2. Send it as a header, in your client config or with curl: 
      "calculatorlib": {
  "url": "https://calculatorlib.com/mcp",
  "headers": { "Authorization": "Bearer clk_…" }
}

    REST API

    Same calculators without an MCP client. Full reference: OpenAPI.

    GET /api/calculators/schemas?q=Search calculators, with input schemas
    POST /api/calculator/execute/<slug>Run a calculator
    GET /api/converter/categoriesConverter categories and units
    POST /api/converter/convertConvert a value

    FAQ

    Is it free?

    Yes. Anonymous calls are free within the rate limit. With a token, your plan sets the monthly quota (pricing).

    What do you log?

    The tool name, field names (not their values), latency, errors, IP and user agent, to stop abuse and improve results. Calls made with a token also appear in your call log.

    Why is structuredContent sometimes missing?

    A few older calculators only return a one-line summary. The number is still in the text.

    Why bmi_calculator and not bmi-calculator?

    Tool names use underscores, so the page /bmi-calculator becomes bmi_calculator.

    I lost my token.

    Tokens are stored as hashes and can’t be shown again. Revoke it in API tokens and create a new one.