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

Annotations already declare a read-only, idempotent, closed-world operation, so the safety profile is covered. The description goes beyond them usefully by listing the computed outputs, which is meaningful here since there is no output schema. It stops short of edge-case behavior (e.g. future dates, default birth date of 1990-01-01).

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?

A single front-loaded sentence carrying the full output list, with no filler. The trailing marketing URL is extraneous for tool selection but does not impede comprehension.

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 two-parameter, read-only calculator with no output schema and no nested objects, the description adequately conveys what the tool computes and returns. Only minor gaps remain: no alternative-tool routing and no mention of the asOf parameter or default birth date 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%, so both parameters (birth, asOf) are documented in structured form and the baseline is 3. The description implies the birth input but never mentions the optional asOf date, adding essentially no meaning beyond the schema.

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 (computes exact age from date of birth) and enumerates the derived outputs (years/months/days, total weeks and days, birth weekday, next-birthday countdown), so its scope is unmistakable. It does not, however, draw any boundary against close siblings like date_difference_calculator or day_of_week_calculator, which share part of this surface.

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?

The description gives no when-to-use guidance and never names an alternative, despite several near-neighbors (date_calculator, date_difference_calculator, day_of_week_calculator, countdown_calculator). An agent must infer from the tool name alone which of these date tools to select.

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