macalc

calculate_percentage

Calculate percentages: value of total, percentage change, what percent. See list_bundles for related 'math' calculators.

Input Schema

TableJSON Schema

Name	Required	Description
`a`	Yes	First value
`b`	Yes	Second value
`operation`	Yes	of: X% of Y; change: from A to B; what_pct: X is what % of Y

Output Schema

TableJSON Schema

Name	Required	Description
`result`	No	Computed result. Object whose fields depend on the tool (e.g. {tax, marginal_rate, brackets} for tax tools, {volume_l, gallons} for volume tools).
`source`	No	Authoritative source for the rule or formula (e.g. "Article 197 CGI", "NF DTU 21").
`formula`	No	Human-readable formula or method used (e.g. "I=P·r·t", "Magnus formula").
`reference_url`	No	Link to a calcul2 page documenting the calculation in detail.

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedApr 25, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "additionalProperties": false,
+  "properties": {
+    "formula": {
+      "description": "Human-readable formula or method used (e.g. \"I=P·r·t\", \"Magnus formula\").",
+      "type": "string"
+    },
+    "reference_url": {
+      "description": "Link to a calcul2 page documenting the calculation in detail.",
+      "type": "string"
+    },
+    "result": {
+      "description": "Computed result. Object whose fields depend on the tool (e.g. {tax, marginal_rate, brackets} for tax tools, {volume_l, gallons} for volume tools)."
+    },
+    "source": {
+      "description": "Authoritative source for the rule or formula (e.g. \"Article 197 CGI\", \"NF DTU 21\").",
+      "type": "string"
+    }
+  },
+  "type": "object"
+}

First observedApr 8, 2026

TDQS

C2.9/5.0

Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations provided, so description carries full burden. It does not disclose any behavioral traits (e.g., no side effects, response format, limitations). For a simple calculator, this is minimal but acceptable.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Two sentences: first directly states purpose, second suggests related tools. Concise and front-loaded, though the second sentence is somewhat tangential.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Has output schema, so return values are covered. Description covers basic purpose but lacks context on how to decide between operations or handle edge cases. Adequate for a simple tool.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema already covers all parameters fully (100% coverage). Description merely reiterates the operation enum values without adding new meaning or usage hints.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

Description clearly states the tool calculates percentages with three specific operations (value of total, percentage change, what percent). It is not fully differentiated from sibling calculate_percentage_change, but the purpose is clear and specific.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines2/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

No guidance on when to use this tool versus alternatives like calculate_percentage_change. The mention of list_bundles is vague and does not provide practical decisions.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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