Age calculator

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

Annotations already declare readOnly, idempotent, and closed-world, so the safety profile is covered. Beyond that, the description discloses a genuine edge case ('Feb 29 birthdays fall on Feb 28 in common years'), the Hijri calendar convention (Umm al-Qura), the accepted date format, and the default display name for the second person. It stops short of saying what happens with invalid or future dates.

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?

The purpose is front-loaded in the opening clause and the rest is a dense but informative feature inventory. The single sentence is long and list-heavy, but since there is no output schema, most of the enumeration earns its place; a short break after the primary purpose would help.

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 four parameters, no output schema, and no nested structures, the description does the heavy lifting by telling the caller what the result contains as well as what it takes to call it. Only error behavior for malformed or impossible dates is left unaddressed.

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 baseline applies. The description adds only light context beyond the schema, restating the ISO YYYY-MM-DD format and that the second person is optional; the onDate 'today' default and otherName's 'They' default are already in 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?

The description gives a specific verb and resource ('Exact age in years, months and days from a date of birth') and then precisely enumerates the scope: totals, weekday, Hijri date and age, next birthday, star sign, Chinese zodiac, 1,000-day milestone, and optional second-person gap. That is far more specific than a generic 'compute' statement. It never names the overlapping siblings calc_date_diff or calc_hijri, so the caller must infer the boundary itself.

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?

Usage is implied by 'from a date of birth' and by the schema default that onDate falls back to today, plus the note that the age gap to a second person is optional. There is no explicit when-to-use/when-not guidance and no pointer to alternatives such as calc_date_diff for day counts or calc_hijri for pure Hijri conversion.

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