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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), but the description adds real value beyond them: it defines what a returned window means (1st–99th percentile from the WHO Motor Development Study) and that inside-window = normal range. It stops short of noting any clinical caveats (e.g. that the locale param carries a paediatrician-authored disclaimer), so not a 5.

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 dense sentences, front-loaded with what is returned and followed by the interpretive definition of a percentile window. No 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 must convey what comes back, and it does so well (window states plus CDC checkpoints and the normal-range interpretation). It could go further on return shape (e.g. per-milestone entries) but the safety profile is already covered by annotations.

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 both parameters are well documented in-schema, including the corrected-age hint and the locale rationale. The description adds only the roundabout 'at a given age' wording, 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 resource and return set: WHO motor-development windows (open/closed/not-yet-due) at a given age plus nearest CDC checkpoint months. This is clearly distinct from the percentile/growth siblings, and no sibling competes on milestones, so an agent can select it without opening the 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?

Usage is only implied by the tool name and the phrase 'at a given age'; there is no explicit when-to-use, when-not-to-use, or named alternative among the many growth siblings. It does not tell the agent how it relates to corrected_age or child_age, which would be the natural pairing.

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