BMI calculator

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

Annotations already declare readOnly/idempotent/closed-world, so the safety profile is covered; the description adds real value on top with validity bounds (height 50–272 cm, weight 10–650 kg, age 18–120 for BMR), conditional behavior (BMR only when age is supplied and is adult), and a liability caveat. No return envelope detail, but the computed outputs are enumerated, so nothing important is hidden.

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

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

Dense and front-loaded: capability list first, then unit systems, then validity bounds, then disclaimers — a sensible order. It is long for an MCP description, though nearly every clause carries information an agent cannot get from the schema or annotations.

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

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

For an 8-parameter all-optional tool with no output schema, the description covers outputs, units, ranges, and the adult-only restriction well. The one real gap is that required-for-success inputs (weight plus a height in the matching unit) and the behavior when heightCm is given under imperial units are never stated.

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

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

Schema coverage is 100%, so the baseline is 3; the description adds the unit-system contract (metric cm/kg vs imperial ft+in/lb) and the numeric domain limits that the schema lacks. It does not explicitly restate which of the 8 optional parameters are actually needed for a valid call (height + weight), leaving that to inference.

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

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

Opens with a specific resource and immediately enumerates the concrete outputs (WHO category, healthy weight range, BMI Prime, waist-to-height ratio, BMR, maintenance/loss calories), so an agent knows exactly what it gets back. It is clearly distinguished from the surrounding calc_* family (calc_age, calc_unit_convert, calc_stats) which do not compute body metrics.

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

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

Gives explicit conditions: adults 18–120 with age get BMR/calories, children need percentile charts instead (a clear when-not), and there's a 'not medical advice' scope caveat. It also states the supported input ranges. It stops short of naming a sibling alternative, but no sibling actually overlaps this function.

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