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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The phrase 'Plain maths, no AI' adds genuinely useful context (deterministic, no model inference, no external lookup), but pagination, precision, and the meaning of the 'Asian cut-offs' behavior are left unexplained.

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?

Two short sentences, the calculator list front-loaded and the differentiating tagline trailing; nothing is padded. It is slightly fragmentary (no explicit verb), but every clause carries information.

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?

This is a multi-mode tool (five calculators, seven parameters, no output schema), and the description omits the parameter-to-calculator mapping, the units/format expectations, and how the Asian cut-off variant is triggered. An agent could call it with the wrong parameter combination and get errors or nonsense without any description-level warning.

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 description coverage is only 29% and the description documents no parameters at all, so the burden was on it to compensate and it does not. It also introduces ambiguity by advertising 'Asian cut-offs' for BMI while the schema exposes no ethnicity or cut-off selector, leaving an agent unable to access that behavior. No mapping of age/height_cm/weight_kg/active/cycle_days/last_period_date to specific calculators is given.

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?

The description names five concrete calculators (BMI, due date, ovulation/fertile window, water intake, heart-rate zones) plus a behavioral tagline 'Plain maths, no AI' that separates it from the explanation-oriented siblings like explain_lab_result or find_health_guide. The verb 'calculates' is only implicit, and no sibling is named, but the resource list is specific enough to distinguish it.

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?

Usage is only implied: an agent can infer this is the tool for deterministic health math rather than AI interpretation, but there is no explicit when-to-use/when-not guidance and no mention of alternatives. Critically, nothing says which supporting parameters each calculator needs, so an agent must guess how to satisfy bmi vs. due_date vs. ovulation.

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