Calc MCP

📖 Documentation — Full tool reference, examples, and install guides.

21 tools for things AI is not good at — deterministic math, cryptographic randomness, accurate date arithmetic, encoding, hashing, and more.

LLMs hallucinate calculations, can't generate true random numbers, and struggle with timezones. This MCP server fixes that.

Quick Start

# Claude Code
claude mcp add -s user calc-mcp -- npx --prefix /tmp -y @coo-quack/[email protected]

# Or just run it
npx --prefix /tmp -y @coo-quack/[email protected]

Works with Claude Desktop, VS Code Copilot, Cursor, Windsurf, and any MCP client — setup guides below.

Windows note: These examples use /tmp as the npx prefix — on Windows, replace it with a writable directory such as C:\Temp.

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Why?

AI alone	With calc-mcp
"10 + 34 × 341 ÷ 23 = 507.8" ❌	514.087 ✅ (math)
"Here's a UUID: 550e8400-..." 🤷 fake	Cryptographically random UUID v4/v7 ✅ (random)
"100 days from now is..." 🤔 guess	2026-05-22 ✅ (date)
"SHA-256 of password123 is..." 💀 hallucinated	{"hash": "ef92b778bafe..."} ✅ (hash)

• Deterministic — Same input, same correct output, every time
• Secure — Sandboxed math, ReDoS protection, weak hash warnings
• Private — All computation runs locally, no data sent to external services
• No server config — Install once via npx; MCP client setup required
• No API key — No account or API key required for calc-mcp itself; requires Node.js

Examples

Ask in natural language — your AI assistant selects the appropriate tool.

Math & Numbers

You ask	You get	Tool
What's 10 + 34 × 341 ÷ 23?	514.087	math
Convert 255 to binary	11111111	base
Is 4539578763621486 a valid card number?	true	luhn

Text & Encoding

You ask	You get	Tool
How many characters in "Hello, World! 🌍"?	15 chars, 18 bytes	count
Base64 encode "Hello World"	SGVsbG8gV29ybGQ=	base64
Base64 decode "eyJhbGciOiJIUzI1NiJ9"	{"alg":"HS256"}	base64
URL-encode "hello world"	hello%20world	encode
URL-decode "hello%20world"	hello world	encode
HTML-decode &lt;script&gt;	<script>	encode
SHA-256 hash of "password123"	{"hash": "ef92b778bafe..."}	hash
HMAC-SHA256 of "message" with key "secret"	{"hash": "8b5f48702995..."}	hash

Date & Time