@retiform/calculator-mcp-server

A scientific calculator MCP tool server for AI agents — safe expression evaluation, symbolic calculus (derivatives, simplification, equation solving, integration), statistics, and matrix operations, over the Model Context Protocol.

Stateless pure math. The agent is the brain; the server is the calculator.

Tools (13)

Every tool description embeds worked examples — an LLM caller learns each tool from the tool itself.

Related MCP server: Math MCP Server

Highlights

• Sandboxed by design. Expressions are parsed to ASTs and audited before evaluation: a symbol allowlist (namespace members + your scope variables), a host-global blocklist enforced in every mode, assignment rejection, and throwing stubs on import/evaluate/createUnit. Escape-vector tests (constructor.constructor, import("fs"), process, globalThis) are first-class and must stay green.

• Exact where possible. Linear/quadratic equations are solved symbolically (rationals as fractions, complex pairs as 1 + 2i); polynomial definite integrals (degree ≤ 4) are exact via antiderivatives that are self-checked (dF/dx ≡ f verified before returning).

• Numeric where not. Transcendental equations: deterministic scan of [-100, 100] with bisection polish. General integrals: adaptive Simpson with an error estimate.

• Statistics you can trust. The t-quantile (continued-fraction incomplete beta + Lanczos log-gamma) matches R's qt() to 15 digits — verified in the test suite against reference values.

• JSON-native matrices. Plain nested arrays in, plain nested arrays out. No library types leak across the wire.

• All transports. stdio (default for the bin entry), HTTP, and SSE — see Configuration.

Install

npm install @retiform/calculator-mcp-server
# or run directly:
npx -y @retiform/calculator-mcp-server

Requires Node.js ≥ 22.

Usage with MCP clients

stdio (Claude Desktop, most clients)

{
  "mcpServers": {
    "calculator": {
      "command": "npx",
      "args": ["-y", "@retiform/calculator-mcp-server"]
    }
  }
}

HTTP / SSE

npx -y @retiform/calculator-mcp-server          # stdio (bin default)
CALC_MCP_TRANSPORT=http npx -y @retiform/calculator-mcp-server   # HTTP on 127.0.0.1:3778
CALC_MCP_TRANSPORT=sse  npx -y @retiform/calculator-mcp-server   # SSE

Library use:

import { createCalculatorMcpServer } from '@retiform/calculator-mcp-server'

const server = createCalculatorMcpServer({ transport: 'http', port: 3778, host: '127.0.0.1' })
await server.start()

Configuration

Precedence: code defaults ← JSON5 config file ← environment variables.

Config file path defaults to ./config.json5 (override with CALC_MCP_CONFIG). See config.example.json5. An explicitly chosen transport always wins over entry defaults.

Security notes

• Expressions are untrusted input. The engine evaluates them in a sandboxed mathjs namespace with an audited AST pipeline — see src/engine/evaluate.js for the threat model and defense layers.

• Scope values must be finite numbers; nothing else crosses the boundary.

• DoS bounds: expression length ≤ 2000 chars, datasets ≤ 1M values, matrix dimensions ≤ 400×400.

• Bind loopback-only deployments unless you explicitly need otherwise; layer firewall rules for anything network-reachable.

Development

npm install
npm test        # vitest: 169 unit + e2e tests
npm run lint    # eslint
npm run format:check

License

MIT

Sponsors

If calculator-mcp-server is useful to you, consider supporting its continued development:

• GitHub Sponsors

• Bitcoin: bc1q0gd3mwjg3zy9sghv22kmpg823vss4c0zzdzg24

• Solana: Eu8wQcW68TKMs1a6eqzZu8znzU52QLqQugAMG8uCD6y6

• Ethereum / EVM: 0x2733ff7c865C56d565a99BE1DC11B81cc76850A5

• XRP Ledger: r4X6e7McAQj7e8vBCeued1RYu4mCJrREDG

Crafted with ❤️ by Retiform Labs