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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint=false, so the safety and determinism profile is fully covered. The description adds only the fact that no child measurement is consumed, which slightly clarifies behavior but adds little beyond the annotations.

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 sentences, front-loaded with what is returned before the usage hint, with zero filler. Every clause earns its place.

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 no output schema, the description usefully states the return shape (the percentile band values). It omits any mention of locale or standard choice, though those are well covered in the schema, leaving only a minor gap for a read-only 5-parameter tool.

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 80% and the schema itself documents sex, locale, standard, and ageMonths (including corrected age and WHO/CDC semantics). The description mentions only age and sex generically, adding no meaning beyond the schema, so the baseline 3 applies.

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 resource (percentile band at 3rd/15th/50th/85th/97th) for a given age and sex, and explicitly contrasts itself with measurement-based siblings by noting 'no child's measurement involved.' An agent can distinguish this from growth_percentile or bmi_percentile 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.

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

Gives a clear usage context — 'Use this to answer what is normal for this age' — which orients the agent toward reference-lookup intent rather than measurement classification. It does not name the specific alternative siblings or state exclusions, so it falls short of the 5 bar.

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