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), and the description adds genuinely new behavioral context: what is returned (percentile, z-score, SGA/AGA/LGA), the caveat that this is a statistical classification not a diagnosis, and the locale behavior for paediatrician-authored disclaimer text. That is real disclosure beyond the structured fields.

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?

Purpose is front-loaded and every sentence does work — the growth-chart contrast and the 2.2 kg example both earn their place. It runs slightly long for a single-purpose lookup tool, but nothing is filler.

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?

With read-only annotations covering safety, a fully documented schema, and the description naming the returned quantities, an agent has nearly everything needed. The absence of an output schema leaves the exact result structure only described rather than specified, which is the one remaining gap.

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 100% and the schema itself carries the important semantics (grams not kilograms, obstetric vs corrected age, 23-41 weeks, sex-specific charts). The description adds no parameter syntax beyond the schema, so a baseline of 3 is appropriate even though the underlying schema is excellent.

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?

States a specific verb and resource — where a birth measurement sits on the Olsen 2010 intrauterine curves — and explicitly distinguishes itself from the growth charts ('not how a child grows over time, but how big they were on the day they were born'). The 34-week vs 40-week example makes the distinct question concrete, so an agent can separate it from growth_percentile and growth_reference_range.

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?

The description gives a clear when-to-use rule and names the conceptual alternative (the growth chart tools), including why WHO charts cannot answer this question. It does not name the sibling tools directly or state explicit exclusion conditions, so it stops just short of a 5.

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