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

Annotations already declare readOnlyHint/idempotentHint/destructiveHint=false, so the safety profile is covered; the description adds substantive non-structured context about what is actually reported and a clear scope limitation (WHO Growth Velocity Standards are not implemented, no percentile is claimed for rate of gain). It does not cover error behavior, but for a pure computation tool this is solid added value.

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?

Three sentences, front-loaded with the return content before the interpretive rule and the exclusion. Dense but every clause carries information; the em-dash aside on band crossings is the only slightly expansive part.

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 and six parameters including nested measurement objects, the description usefully previews what comes back (two percentiles, two z-scores, a shift, a band-crossing count). Since the output schema is absent, it could be a touch more explicit about the response shape, but the essentials are present.

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 83%, so the standard, locale, sex, metric and age fields are already documented in-schema. The description mentions band lines (3rd/15th/50th/85th/97th) and 'same child' but adds no syntax or format meaning for the actual parameters, 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 a specific computation on a specific resource ('what moved between two measurements of the same child') and enumerates the outputs: percentile and z-score at each point, positional shift, and band lines crossed. It also explicitly distinguishes itself from the sibling growth_velocity by denying it is a velocity percentile, so an agent can route 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 real selection context: band crossings are the clinically meaningful unit, one crossing is common while two downward is the pattern clinicians review, and it rules out the velocity-percentile use case (which points at the growth_velocity sibling). It stops short of naming that sibling or stating prerequisites explicitly, so no full 5.

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