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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered. The description adds real behavioral context beyond that: the prematurity exclusion and the YYYY-MM-DD date convention. It does not mention that output includes clinical disclaimer text, which the locale parameter hints at but the description never surfaces.

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, each load-bearing: what it returns, when to use it, and the key semantic caveat. The most important distinction (chronological vs corrected age) is front-loaded rather than buried.

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?

No output schema exists, so the description correctly spells out the return shape (years/months/days plus totals). Combined with 100% schema coverage and clear annotations, an agent has everything needed to select and call it.

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 the schema already documents birthDate, asOf and locale in detail, including the locale's clinical-safety rationale. The description only restates the date format, adding nothing beyond the structured fields. Baseline 3 is appropriate.

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 verb and resource: it computes exact calendar age from a birth date, and enumerates the output components (whole years, months, leftover days, totals in months/weeks/days). It also explicitly separates itself from the corrected_age sibling, so an agent can identify 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?

Concrete trigger phrases are given ('how old is my baby in months', 'age in weeks') plus the when-not case ('not the age corrected for prematurity'). It stops short of naming corrected_age outright as the tool to use for preemies, so the routing is implied rather than fully explicit.

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