TrueCalc
← AI agents

Five questions a model gets wrong

None of these are prompting problems. Each one has an answer that depends on an algorithm, a calendar or a rounding rule — none of which a language model has access to by thinking harder.

workbook.truecalc.appOpen in full
Monthly payment
1,403.83

B2

Working days, Q1 2026
64

B3

90th percentile
73.2

B6

Verified at build timeThese figures are produced by running the grid above through the engine during the build. If the engine ever disagrees with them, this page does not ship.

Every value in this grid was checked against an independent implementation before it was published, not read off the engine and trusted.

The same thing, in code

Nothing here is playground-only.

The grid above and the snippet below run the same engine. Whatever you can do in the sheet, you can do from your own program.

// Your agent calls a tool instead of guessing.
{
  "name": "evaluate",
  "arguments": {
    "formula": "NETWORKDAYS(DATE(2026,1,1),DATE(2026,3,31))"
  }
}

// => { "type": "number", "value": 64 }

Take it further

Shipped today. One command — npx -y @truecalc/mcp — gives any MCP client twelve tools over stdio. Nothing leaves your machine.

Open the full playgroundInstall the engine

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