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

Annotations already declare readOnly, idempotent, non-destructive and closed-world behavior, so the safety profile is covered. The description adds the scoping constraint (no child's measurement involved) but says nothing about validity ranges, boundary behavior, or output format beyond the percentile list.

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 compact sentences, front-loaded with what the tool returns and followed by the usage cue. Every clause earns its place with no redundancy.

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 a read-only reference lookup with rich annotations, 80% schema coverage and no output schema, the description is nearly sufficient: it names the returned percentile band and the scope. It could still note output shape or edge cases, but the core is covered.

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%, so the schema already carries most parameter meaning (sex, locale, standard, ageMonths are all documented there). The description only echoes 'age and sex' and adds no syntax or constraint detail beyond what the schema provides, so 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 specifically what it returns (the 3rd/15th/50th/85th/97th percentile values for an age and sex) and clarifies the scope as 'the reference band itself, with no child's measurement involved'. This functionally distinguishes it from measurement-based siblings like growth_percentile or bmi_percentile, though it does not name one directly.

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 usage: "Use this to answer 'what is normal for this age'." That is a clear condition for when to use it, but there are no explicit when-not statements or named alternatives for the adjacent measurement tools.

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