datetime.age

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

Annotations already declare readOnly/closed-world, and the description adds genuinely non-obvious behavior: omitting reference_date makes results depend on the server's execution date, the birthday boundary rule (age increments on the birthday itself), and the error condition. This is exactly the kind of context annotations cannot carry.

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 sentences, each carrying distinct information (purpose, format/boundary rule, default behavior, error/scope exclusion), with purpose front-loaded. Dense but no filler; the 세는나이 exclusion could be framed more directly as guidance.

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?

Output schema exists, so return shape need not be described. Inputs, default, boundary rule, and error case are all covered; the only real gap is the timezone behind the server-default date.

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 0%, so the description must compensate, and it does: it specifies the YYYY-MM-DD format for both dates, that reference_date is optional and defaults to the server's today, and the invalid-ordering error. It stops short of stating the server timezone, which matters for the default.

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 computation (Korean legal age in years/months/days as integers) and scopes it against the obvious confusable concept by declaring 세는나이 is not computed. An agent can tell this apart from datetime.diff or datetime.day_count without opening any 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?

Gives clear operating context: reference_date may be omitted (server today is used), and a reference date earlier than the birth date is an error. It does not explicitly name a sibling alternative for the counting-age case, only excluding it, so it stops short of full when/when-not routing.

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