Evaluate math expressions, run trig/stats, and convert units via @slbdn/cruncher-mcp (npx)

Recipe: Scientific calculator via @slbdn/cruncher-mcp (npx)

What it is

A zero-dependency MCP server (MIT, v1.2.30) that exposes 34 calculator tools in "standard" tier (43 in "full" tier) across 8 categories: arithmetic, expression evaluation, trigonometry, logarithms, statistics, percentages, unit conversion, and scientific constants. Uses worker_threads for timeout protection (3s default) and integer-scaling for floating-point accuracy.

Spawn

npx -y @slbdn/cruncher-mcp

No API keys, no env vars needed. Optionally set CRUNCHER_TOOL_SET=full for all 43 tools (adds memory functions).

MCP handshake

→ {"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"probe","version":"1.0.0"}}}
← {"result":{"protocolVersion":"2024-11-05","capabilities":{"tools":{}},"serverInfo":{"name":"Cruncher","version":"1.2.30"}}}

Verified tool calls (8 runs, 8 successes)

1. evaluate_expression — safe math expression parser (no eval, whitelist regex)

→ tools/call: {"name":"evaluate_expression","arguments":{"expression":"(5 + 3) * 10 / 2"}}
← {"content":[{"type":"text","text":"40"}]}  // 30ms

2. sine — trigonometry with degree/radian support

→ tools/call: {"name":"sine","arguments":{"angle":45,"unit":"degrees"}}
← {"content":[{"type":"text","text":"0.7071067811865475"}]}  // 2ms

3. factorial — with worker_thread timeout protection

→ tools/call: {"name":"factorial","arguments":{"n":10}}
← {"content":[{"type":"text","text":"3628800"}]}  // 21ms

4. get_constant — math, physics, and chemistry constants

→ tools/call: {"name":"get_constant","arguments":{"name":"pi"}}
← {"content":[{"type":"text","text":"3.141592653589793"}]}  // 1ms

5. add — floating-point precision via integer-scaling

→ tools/call: {"name":"add","arguments":{"a":0.1,"b":0.2}}
← {"content":[{"type":"text","text":"0.3"}]}  // ← NOT 0.30000000000000004!

6. std_dev — sample standard deviation

→ tools/call: {"name":"std_dev","arguments":{"numbers":[10,20,30,40,50]}}
← {"content":[{"type":"text","text":"15.811388300841896"}]}

7. variance — sample variance

→ tools/call: {"name":"variance","arguments":{"numbers":[10,20,30,40,50]}}
← {"content":[{"type":"text","text":"250"}]}

8. convert_unit — 80+ conversions across 8 categories

→ tools/call: {"name":"convert_unit","arguments":{"value":100,"category":"length","from":"km","to":"mi"}}
← {"content":[{"type":"text","text":"{\"value\":100,\"from\":\"km\",\"to\":\"mi\",\"result\":62.1371192237334,\"category\":\"length\"}"}]}

→ tools/call: {"name":"convert_unit","arguments":{"value":100,"category":"temperature","from":"C","to":"F"}}
← {"content":[{"type":"text","text":"{\"value\":100,\"from\":\"C\",\"to\":\"F\",\"result\":212,\"category\":\"temperature\"}"}]}

→ tools/call: {"name":"convert_unit","arguments":{"value":1,"category":"digital_storage","from":"GB","to":"MB"}}
← {"content":[{"type":"text","text":"{\"value\":1,\"from\":\"GB\",\"to\":\"MB\",\"result\":1024,\"category\":\"digital_storage\"}"}]}

All 34 tools (standard tier)

add, subtract, multiply, divide, power, sqrt, sine, cosine, tangent, asin, acos, atan, logarithm, natural_log, absolute, get_constant, sum, avg, median, min, max, count, range, variance, std_dev, percentage_of, percentage_change, percentage_reverse, modulo, factorial, evaluate_expression, convert_unit, set_angle_mode, get_angle_mode

Gotchas

• Tool name is convert_unit (singular), not convert_units
• Tool name is std_dev, not standard_deviation
• convert_unit requires category field (length, weight, temperature, area, volume, time, speed, digital_storage)
• Default tier is "standard" (34 tools) — set env CRUNCHER_TOOL_SET=full for memory functions (M+, M-, MR, MC)
• Constants cover Math (pi, e, tau, phi, sqrt2), Physics (c, g, G, h, k, R), and Chemistry (NA