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

Annotations already cover the read-only, idempotent, non-destructive profile, and the description adds far more: the return fields, the pre-due-date edge case where no corrected age exists and days remaining are reported, the ~24-month cut-off, and the calendar-date format.

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?

Front-loaded with the definition and formula before usage and edge cases; five dense sentences with no filler, though the milestone/plotting enumeration is slightly longer than needed given sibling tools cover those areas.

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 compensates by enumerating the returned values and the pre-due-date/no-correction edge cases, so an agent knows exactly what it will get and when the result is undefined.

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 asOf, locale, gestationalDays and gestationalWeeks are already documented in the schema. The description only restates that it takes birth date and gestational age and that dates are YYYY-MM-DD, adding little beyond the structured fields — baseline 3.

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 precise verb+resource (computes the corrected/adjusted age) and gives the exact formula ('age since birth minus the weeks the baby was early'), which distinguishes it from generic sibling tools like child_age or growth_percentile.

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?

Names concrete use cases (answering 'my preemie's corrected age', reading milestones, choosing the plotting age) and an implicit exclusion ('a baby born at 37 weeks or later needs no correction'), but never names an alternative sibling such as child_age or growth_percentile to route term babies to.

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