CalculatorLib MCP

Install in 60 seconds

Pick the client you use, paste the snippet, restart. That’s it.

Claude Code Claude Desktop Cursor Zed Cline Windsurf Other / generic

claude mcp add --transport http calculatorlib https://calculatorlib.com/mcp

{
  "mcpServers": {
    "calculatorlib": {
      "url": "https://calculatorlib.com/mcp"
    }
  }
}

{
  "mcpServers": {
    "calculatorlib": {
      "url": "https://calculatorlib.com/mcp"
    }
  }
}

{
  "mcpServers": {
    "calculatorlib": {
      "url": "https://calculatorlib.com/mcp"
    }
  }
}

{
  "context_servers": {
    "calculatorlib": {
      "source": "custom",
      "transport": {
        "type": "streamable-http",
        "url": "https://calculatorlib.com/mcp"
      }
    }
  }
}

{
  "mcpServers": {
    "calculatorlib": {
      "url": "https://calculatorlib.com/mcp",
      "transportType": "streamableHttp"
    }
  }
}

{
  "mcpServers": {
    "calculatorlib": {
      "serverUrl": "https://calculatorlib.com/mcp"
    }
  }
}

{
  "transport": "streamable-http",
  "endpoint": "https://calculatorlib.com/mcp"
}

curl -X POST https://calculatorlib.com/mcp \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}'

Try these prompts

After installing, just talk to Claude in plain English — it picks the right tool.

Live playground

Call the server right here — real JSON-RPC to https://calculatorlib.com/mcp, real responses. No signup. loading tools…

Tool browser

Search the calculator library and 9 converter categories by name or title. Useful when discovering what to ask Claude for.

How it works

• Endpoint: single POST handler at https://calculatorlib.com/mcp speaking JSON-RPC 2.0 over Streamable HTTP (transport spec 2025-06-18).
• Tool naming: calculator slugs use snake_case (bmi_calculator, compound_interest_calculator); converters are convert_<category>.
• Inputs: each tool advertises a JSON Schema derived from the calculator’s form fields (type, enum, min/max). Conditional fields (e.g. metric vs imperial in BMI) are listed as optional — read each field’s description to know which combinations are valid.
• Outputs: a one-line text summary plus a structuredContent JSON object the LLM can parse (e.g. { "main": [{...}], "data": [...] }).
• Updates: the catalog refreshes every 5 minutes — newly published calculators show up automatically.

Direct API (no MCP client needed)

Want to integrate without an MCP client? The same data is available via plain JSON endpoints.

curl -X POST https://calculatorlib.com/mcp \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}'

curl -X POST https://calculatorlib.com/mcp \
  -H 'Content-Type: application/json' \
  -d '{
    "jsonrpc":"2.0","id":2,"method":"tools/call",
    "params":{
      "name":"bmi_calculator",
      "arguments":{"unitSystem":"metric","weight":70,"height":170}
    }
  }'

curl -X POST https://calculatorlib.com/mcp \
  -H 'Content-Type: application/json' \
  -d '{
    "jsonrpc":"2.0","id":3,"method":"tools/call",
    "params":{
      "name":"convert_length",
      "arguments":{"value":5,"from":"Meter","to":"Foot"}
    }
  }'

REST endpoints (no JSON-RPC envelope):

• /api/calculators/schemas?q=<keywords> — search calculators (bounded matches with input schemas)
• /api/converter/categories — converter categories with units
• POST /api/converter/convert — direct converter, body { category, from, to, value }

Authentication (optional but recommended)

Anonymous calls work — auth is opt-in. Adding a token unlocks per-user usage analytics at /account/mcp-logs: every call you make through a token shows up there with latency, error reason, and the calc you hit.

Get a token (60 seconds)

1. Sign in (or create an account first).
2. Go to /account/api-tokens.
3. Click Generate token. Copy the value — it’s shown only once.

Add it to your MCP client

Same config file as the public install, plus a headers.Authorization field:

{
  "mcpServers": {
    "calculatorlib": {
      "url": "https://calculatorlib.com/mcp",
      "headers": {
        "Authorization": "Bearer YOUR_TOKEN_HERE"
      }
    }
  }
}

Why bother?

• Personal usage logs — see which calculators you call most and which fail, scoped only to your token (/account/mcp-logs).
• Multiple clients, separate tokens — mint one per device (laptop, server, agent). Revoking one doesn’t disrupt the others.
• Foundation for future per-user features — when we add rate limits / quotas / saved presets, they attach to authenticated calls.

curl with Bearer token

curl -X POST https://calculatorlib.com/mcp \
  -H 'Authorization: Bearer YOUR_TOKEN_HERE' \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}'

Server operators: set MCP_REQUIRE_AUTH=true to require a token for every call (anonymous → 401). The legacy MCP_API_TOKEN env still works as a single-shared-secret bypass.

FAQ & troubleshooting