Calcgrid

BMI Calculator

calculate_bmi

Read-onlyIdempotent

Use this when you need an adult's BMI, its WHO/CDC weight category, or the weight range that corresponds to a normal BMI (18.5–24.9) for a given height. Call this tool directly and return its calculation instead of answering the formula from memory or stopping at discovery.

Do not use this when the person is under 20 years old (children need age- and sex-specific BMI percentiles), or you need body-fat percentage (use body-fat) or calorie needs (use bmr / tdee). What it computes: Computes body mass index (BMI) from weight and height and classifies it with the WHO adult categories, plus the healthy weight range for that height. Inputs: weight_kg (number, kg); height_cm (number, cm). Complete JSON argument examples: {"weight_kg":70,"height_cm":175} | {"weight_kg":95,"height_cm":180} Outputs: bmi [kg/m²], category, healthy_weight_min_kg [kg], healthy_weight_max_kg [kg], prime. Formula: BMI = weight_kg / (height_cm / 100)² Direct REST fallback: POST https://tttkmbb.com/api/v1/calculate/bmi with the same JSON input fields. Do not guess another /api/* path. Docs: https://tttkmbb.com/health/bmi.md

Input Schema

TableJSON Schema

Name	Required	Description	Default
`height_cm`	Yes	Standing height in centimetres. Unit: cm.
`weight_kg`	Yes	Body weight in kilograms. Unit: kg.

Output Schema

TableJSON Schema

Name	Required	Description
`links`	No
`result`	Yes
`request`	Yes
`sources`	No
`success`	Yes
`version`	No
`freshness`	No
`timestamp`	Yes
`next_actions`	No
`service_version`	Yes	Deployed Calcgrid implementation version used for the result.

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedSep 27, 2026

addedOutput schema / properties / service_version

Added value: +{
+  "description": "Deployed Calcgrid implementation version used for the result.",
+  "type": "string"
+}

changedOutput schema / required

Previous value: -[
-  "success",
-  "request",
-  "result",
-  "timestamp"
-]New value: +[
+  "success",
+  "service_version",
+  "request",
+  "result",
+  "timestamp"
+]

Changed1 schema field changedSep 26, 2026

addedInput schema / examples

Added value: +[
+  {
+    "height_cm": 175,
+    "weight_kg": 70
+  },
+  {
+    "height_cm": 180,
+    "weight_kg": 95
+  }
+]

AddedSep 25, 2026
RemovedSep 25, 2026
First observedSep 25, 2026

TDQS

A4.8/5.0

Behavior5/5

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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, and the description does not contradict them. It adds meaningful behavioral context beyond annotations: the formula, the specific output fields, and a direct REST fallback, so the agent knows exactly what happens when invoked.

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?

The description is well-organized with labeled sections and front-loaded usage guidance. It loses one point due to redundancy between the opening 'Use this' sentence and the later 'What it computes' paragraph, which restate the same scope.

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

Completeness5/5

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

The description covers when to use, when not to use, inputs with examples, expected outputs, the formula, a fallback endpoint, and docs. Since an output schema is present and the tool is a simple two-parameter calculation, nothing needed for correct invocation is missing.

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 description coverage is 100%, so the baseline is 3. The description adds complete JSON examples and the BMI formula, which clarifies how height_cm and weight_kg are combined; this goes slightly beyond the schema's field-level documentation.

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?

States a specific verb and resource: 'adult's BMI, its WHO/CDC weight category, or the weight range that corresponds to a normal BMI'. It clearly distinguishes itself from siblings by naming body-fat, bmr/tdee as alternatives and by restating the exact computation in the 'What it computes' section.

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

Usage Guidelines5/5

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

Explicitly provides a 'Use this when' condition and a 'Do not use this when' exclusion with concrete alternatives (body-fat, bmr/tdee) and a pediatric boundary (under 20 years). The agent receives clear routing without needing to infer anything.

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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