On the Register

waist_ratio

Waist-to-height ratio from waist and height, against the NICE bands (keep your waist under half your height). Flags central-fat risk that BMI can miss. For adults with BMI under 35. General information, not a diagnosis.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "waist_cm": "<waist_cm>",
      "height_cm": "<height_cm>"
    },
    "name": "waist_ratio"
  }
}

Input Schema

Name	Required	Description	Default
`waist_cm`	Yes	Waist measurement in cm (40-200), at the belly button
`height_cm`	Yes	Height in cm (120-230)

Schema Changelog

Changes observed during successful MCP inspections.

First observedNov 7, 2026

TDQS

A4.2/5.0

Behavior4/5

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

With no annotations, the description carries the full burden and does well: it discloses the interpretation basis (NICE bands), the clinical rationale, the population restriction, and a scope disclaimer ('General information, not a diagnosis'). It omits only that this is a pure side-effect-free calculation with no stored state or external lookup, which is inferable but not stated.

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

Conciseness5/5

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

Three short sentences, front-loaded with what it computes before the interpretation, the population limit, and the disclaimer. No filler, no repetition of the title or schema.

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?

For a two-parameter calculator with no output schema, the description implies the return content (a ratio judged against NICE bands, plus a risk flag) and warns about the non-diagnostic nature. It could be slightly more explicit about what the output contains, but nothing an agent needs in order to call it correctly is missing.

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 coverage is 100% — both parameters carry descriptions with units and valid ranges (40–200 cm, 120–230 cm) plus a measurement landmark ('at the belly button'). The description adds no parameter-level detail beyond restating waist and height, so the baseline 3 applies: the schema does the work.

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 computation (waist-to-height ratio from waist and height), the reference standard it is judged against (NICE bands, 'waist under half your height'), and explicitly distinguishes itself from the sibling bmi_check by noting it 'flags central-fat risk that BMI can miss.' An agent can choose between this and bmi_check without opening either schema.

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?

Provides a clear applicability boundary — 'For adults with BMI under 35' — which is a real when-to-use constraint that would otherwise cause misuse in children or high-BMI adults. It does not explicitly name an alternative for out-of-scope cases (e.g. 'use bmi_check for BMI ≥ 35'), so it falls short of the 5-level routing guidance.

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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