@cyanheads/calculator-mcp-server

A calculator MCP server that lets any LLM verify mathematical computations. Evaluate, simplify, and differentiate expressions via a single tool. Powered by math.js v15.

1 Tool · 1 Resource

Public Hosted Server: https://calculator.caseyjhand.com/mcp

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Tools

One tool for all mathematical operations:

Tool Name	Description
calculate	Evaluate math expressions, simplify algebraic expressions, or compute symbolic derivatives.

calculate

A single tool covering 100% of the server's purpose. The operation parameter defaults to evaluate, so the common case is just { expression: "..." }.

• Evaluate — arithmetic, trigonometry, logarithms, statistics, matrices, complex numbers, unit conversion, combinatorics
• Simplify — reduce algebraic expressions symbolically (e.g., 2x + 3x -> 5 * x). Supports algebraic and trigonometric identities
• Derivative — compute symbolic derivatives (e.g., 3x^2 + 2x + 1 -> 6 * x + 2)
• Variable scope via scope parameter: { "x": 5, "y": 3 }
• Configurable precision for numeric results
• Blank optional variable and precision values from form-based MCP clients are treated as omitted

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Resources

URI Pattern	Description
calculator://help	Available functions, operators, constants, and syntax reference.

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Features

Built on @cyanheads/mcp-ts-core:

• Declarative tool definitions — single file per tool, framework handles registration and validation
• Unified error handling across all tools
• Structured logging with optional OpenTelemetry tracing
• Runs locally (stdio/HTTP) or in Docker

Calculator-specific:

• Hardened math.js v15 instance — dangerous functions disabled, evaluation sandboxed via vm.runInNewContext() with timeout
• No auth required — all operations are read-only and stateless
• Input validation: expression length limits, expression separator rejection (semicolons and newlines), variable name regex enforcement
• Result validation: blocked result types (functions, parsers, result sets), configurable max result size
• Scope sanitization: numeric-only values, prototype pollution prevention (blocked __proto__, constructor, etc.)

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Getting Started

Public Hosted Instance

A public instance is available at https://calculator.caseyjhand.com/mcp — no installation required. Point any MCP client at it via Streamable HTTP:

{
  "mcpServers": {
    "calculator": {
      "type": "streamable-http",
      "url": "https://calculator.caseyjhand.com/mcp"
    }
  }
}

Self-Hosted / Local

Add to your MCP client config (e.g., claude_desktop_config.json):

{
  "mcpServers": {
    "calculator": {
      "type": "stdio",
      "command": "bunx",
      "args": ["@cyanheads/calculator-mcp-server@latest"]
    }
  }
}

Prerequisites

• Bun v1.2.0 or higher

Installation

1. Clone the repository:

git clone https://github.com/cyanheads/calculator-mcp-server.git

2. Navigate into the directory:

cd calculator-mcp-server

3. Install dependencies:

bun install

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Configuration

Variable	Description	Default
CALC_MAX_EXPRESSION_LENGTH	Maximum allowed expression string length (10–10,000).	1000
CALC_EVALUATION_TIMEOUT_MS	Maximum evaluation time in milliseconds (100–30,000).	5000
CALC_MAX_RESULT_LENGTH	Maximum result string length in characters (1,000–1,000,000).	100000
MCP_TRANSPORT_TYPE	Transport: stdio or http.	stdio
MCP_HTTP_PORT	Port for HTTP server.	3010
MCP_AUTH_MODE	Auth mode: none, jwt, or oauth.	none
MCP_LOG_LEVEL	Log level (RFC 5424).	info

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Running the Server

Local Development

• Build and run the production version:

  bun run build
  bun run start:http   # or start:stdio

• Run checks and tests:

  bun run devcheck     # Lints, formats, type-checks
  bun run test         # Runs test suite

Docker

docker build -t calculator-mcp-server .
docker run -p 3010:3010 calculator-mcp-server

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Project Structure

Directory	Purpose
src/mcp-server/tools/	Tool definitions (*.tool.ts).
src/mcp-server/resources/	Resource definitions (*.resource.ts).
src/services/	Domain service integrations (MathService).
src/config/	Environment variable parsing and validation with Zod.
docs/	Generated directory tree.

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Development Guide

See AGENTS.md or CLAUDE.md for development guidelines and architectural rules. The short version:

• Handlers throw, framework catches — no try/catch in tool logic
• Use ctx.log for logging
• Register new tools and resources in src/index.ts

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Contributing

Issues and pull requests are welcome. Run checks before submitting:

bun run devcheck
bun run test

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License

Apache-2.0 — see LICENSE for details.