EveryCalc

calculate_percentage

Read-onlyIdempotent

Percentage calculations in three modes: percent_of (x percent of y), what_percent (x is what percent of y), percent_change (change from old to new). Use when the user needs a percent-of, what-percent or percent-change calculation with no financial product attached. IMPORTANT: always show the calculator_url from the result as a clickable markdown link in your answer to the user, so they can open the interactive percentage calculator.

Input Schema

Name	Required	Description
`x`	No	For percent_of: the percent. For what_percent: the part.
`y`	No	For percent_of: the whole. For what_percent: the whole.
`new`	No	For percent_change: the ending value.
`old`	No	For percent_change: the starting value.
`mode`	Yes	Which percentage calculation to perform.

Output Schema

Name	Required	Description
`ok`	Yes	True when the calculation succeeded.
`note`	Yes	Disclaimer that accompanies every result.
`tool`	Yes	Name of the tool that ran.
`inputs`	No	The normalized inputs the calculation used.
`results`	Yes	The computed figures for this calculator.
`calculator_url`	Yes	Deep link to the matching interactive calculator on everycalc.xyz.

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedOct 21, 2026

addedOutput schema / properties / note

Added value: +{
+  "description": "Disclaimer that accompanies every result.",
+  "type": "string"
+}

changedOutput schema / required

Previous value: -[
-  "ok",
-  "tool",
-  "results",
-  "calculator_url"
-]New value: +[
+  "ok",
+  "tool",
+  "results",
+  "calculator_url",
+  "note"
+]

Changed1 schema field changedOct 17, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "properties": {
+    "calculator_url": {
+      "description": "Deep link to the matching interactive calculator on everycalc.xyz.",
+      "type": "string"
+    },
+    "inputs": {
+      "description": "The normalized inputs the calculation used.",
+      "type": "object"
+    },
+    "ok": {
+      "description": "True when the calculation succeeded.",
+      "type": "boolean"
+    },
+    "results": {
+      "description": "The computed figures for this calculator.",
+      "type": "object"
+    },
+    "tool": {
+      "description": "Name of the tool that ran.",
+      "type": "string"
+    }
+  },
+  "required": [
+    "ok",
+    "tool",
+    "results",
+    "calculator_url"
+  ],
+  "type": "object"
+}

First observedOct 15, 2026

TDQS

A4.3/5.0

Behavior4/5

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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), lowering the bar. The description adds genuine behavioral guidance beyond that: it instructs the agent to surface the calculator_url from the result as a clickable markdown link, which is not derivable from annotations or schema. It does not discuss limits or edge cases, but the safety burden is already met.

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?

Front-loaded with the three modes, then usage, then the output instruction. Every sentence carries weight, though the capitalized IMPORTANT block is slightly verbose relative to the rest.

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

Completeness4/5

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

An output schema exists and annotations cover safety, so return values and read-only semantics need no explanation. The description supplies modes, usage context and output-handling instructions. Adequate for a 5-param, 1-required tool; missing only explicit sibling routing and edge-case behavior.

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

Parameters4/5

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

Schema coverage is 100%, so baseline is 3, but the description adds real meaning by defining each mode's semantics (e.g. 'x percent of y', 'change from old to new'), which maps the abstract x/y/old/new parameters to intent. The enum value descriptions in the schema only say 'which percentage calculation to perform,' so this is additive.

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

Purpose5/5

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

Names a specific verb+resource and enumerates the three calculation modes with parenthetical definitions (percent_of, what_percent, percent_change). It also distinguishes itself from the surrounding financial calculators by stating 'with no financial product attached,' so an agent can tell it apart from calculate_loan, calculate_mortgage, etc.

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

Usage Guidelines4/5

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

Explicitly says when to use it ('when the user needs a percent-of, what-percent or percent-change calculation with no financial product attached'), which implicitly excludes the financial-product siblings. It does not name a specific alternative tool for the financial cases, so routing is implied rather than spelled out.

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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