Jarroba Tools · Calculation

@jarroba/mcp-calc

An MCP server for the maths a language model gets wrong — and, above all, for the ones it gets wrong silently.

claude mcp add jarroba-calc -- npx -y @jarroba/mcp-calc

// Claude Desktop, Cursor, Cline, VS Code…{ "mcpServers": { "jarroba-calc": { "command": "npx", "args": ["-y", "@jarroba/mcp-calc"] } } }

5 tools · ~1.6k tokens of context · stdio, runs on your machine · nothing is uploaded, no API key.

Why this exists

A model that gets 17 * 23 wrong is not the problem: that one is easy to catch. The problem is the answer that looks right.

• 5 km + 300 m. Not a hard sum — but is the answer 305, 5.3, or 5300? A dimensional slip produces a number, not an error, and the number travels into the next formula.
• x^3 - 1 = 0. «x = 1» is true, and it is also only a third of the answer. A tool that stops there and says nothing teaches the caller that there was nothing else.
• 9.8 m/s^2 * t^2 / 2. Here m, s and t are all names of units and perfectly ordinary variable names. Read them wrong and you get a plausible quantity in the wrong dimension.

So every tool here reports how sure it is, not just what it found: exact or approximate, over which interval it searched, how many complex roots it is not showing, and which names it read as units. The one thing none of them will do is fill a gap with something plausible.

The tools

What it will not do

• No symbolic simplification. It was the obvious sixth tool and it was dropped after measuring: the engine leaves (x+1)^2 - (x-1)^2 untouched (it is 4x) and does not know sin²+cos²=1. A tool that hands back your own input under the label "simplified" is worse than no tool, because the caller cannot tell «already simplest» from «I could not do it».
• No integrals, no limits, no inequalities. Not supported, and said so here rather than discovered at the wrong moment.
• Steps beyond degree 2 for equations. calc_solve still answers exactly; what is missing is the explanation, and calc_steps says which cases it covers in every response.

Where it comes from

The engine is the same code that runs the calculator at jarroba.com/tools — pure TypeScript, ~200 unit tests, no server. This package is the whole catalogue filtered down to the calculation domain; if you want the other 95 tools (logs, tests, SQL, SPARQL, diagrams…), install @jarroba/mcp instead. You can also widen this one without switching packages: JARROBA_MCP_DOMAINS=calc,core.

MIT. Nothing here talks to the network. Source: github.com/Invarato/jarroba-mcp.