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

Annotations already declare readOnlyHint=true, destructiveHint=false, idempotentHint=true, and openWorldHint=false, so safety and side-effect expectations are fully covered. The description adds that the calculation is calendar age since birth, not corrected age, which is meaningful behavioral context. However, it does not mention what the response looks like (no output schema), so the return shape remains opaque.

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?

Four compact sentences front-load the result shape, then give usage examples, the prematurity exclusion, and the date format. No repetition or filler.

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?

For an idempotent read-only age calculator with full schema coverage and no output schema, the description is nearly complete: purpose, triggers, exclusion, and date format are all present. The only gap is that it does not describe the return structure, though the schema's explicit total-in-units language partly compensates.

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 coverage is 100%, and the schema descriptions for asOf and locale are unusually rich, including the UTC midnight caveat and the clinical-safety rationale for locale. The description adds only the YYYY-MM-DD format reminder for birthDate, which the schema already states. Baseline 3 applies because the schema does the heavy lifting.

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?

The description states a precise verb and resource: given a birth date, it computes exact calendar age broken into years, months, and leftover days, plus totals in months, weeks, and days. It also explicitly distinguishes itself from the sibling corrected_age by saying it is 'the age since birth, not the age corrected for prematurity'.

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?

It gives concrete trigger phrases ('how old is my baby in months', 'age in weeks') and explicitly names the excluded use case (corrected age for prematurity), routing the agent to corrected_age. The boundary between the two age tools is clear without opening schemas.

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