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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered for what is a pure deterministic computation. The description adds the enumerated return fields, but that largely restates the existing output schema, so net new behavioral insight is modest.

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 compact sentences, front-loaded with the core action before the return values. The inline return-field list is somewhat redundant given an output schema exists, but it is short and does not bloat the definition.

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 a single-parameter calculator with full annotations and an output schema, the definition covers what the tool does and what it returns. The only meaningful gap is the unaddressed ambiguity against calculate_age_in_units, which is a usage-guideline issue rather than a completeness failure of core behavior.

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 the birth_date field is documented as 'YYYY-MM-DD — Date of birth' in the schema itself. The description only echoes 'from a birth date' without adding format, range, or edge-case (e.g., future dates) semantics, 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 verb+resource ('Calculate exact age ... from a birth date') with the unit of output (years, months, days), which is clear standalone. However, it does not distinguish itself from the very close sibling calculate_age_in_units, nor from the many animal-age tools (calculate_cat_age, calculate_dog_age), so sibling differentiation is missing.

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?

There is no when-to-use or when-not-to-use guidance. The trailing 'See list_bundles for related temps-rh calculators' is a bundle cross-reference, not usage context, and it does not tell the agent when to pick this tool over calculate_age_in_units.

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