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

Annotations already establish readOnly/idempotent/non-destructive, so safety is covered. The description adds real domain context: what an open/closed/not-yet-due window means and that a child inside the 1st–99th percentile window is within normal range. It does not mention the physician-authored disclaimer/clinician note that the locale parameter implies is returned, which is a minor gap.

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 front-loaded sentences with no filler; the core purpose (what windows are returned) leads, and the percentile interpretation follows. Slightly dense but every clause carries information.

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 does the necessary work of explaining what is returned (window states plus CDC checkpoint months) and how to read the percentile ranges. It leaves the physician disclaimer/clinician-note return value implicit, but is otherwise complete for a two-parameter read 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 100%, so both ageMonths and locale are already fully documented at a high level of detail (corrected age, language intent, bounds). The description adds no syntax or format detail beyond the schema, 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?

Specific verb+resource: returns WHO motor-development windows (open/closed/not-yet-due) at a given age, plus nearest CDC checkpoint months. This clearly separates it from percentile/growth siblings like growth_percentile or bmi_percentile. 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 implied by 'at a given age,' but there is no explicit when-to-use guidance, no prerequisite statements, and no mention of alternatives among the many growth/percentile siblings. An agent must infer that this is the milestone-window tool versus the percentile tools.

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