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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so the safety profile is fully covered and the bar is lower. The description adds the return-value breakdown, which is genuinely useful since no output schema exists, but it says nothing about timezone/date-format edge cases or failure behavior for invalid 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?

A single sentence with zero filler, front-loaded with the core purpose and followed by the output components. Nothing is wasted.

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 simple two-parameter read-only calculation, the description plus annotations plus a fully documented schema cover what an agent needs. The only gap is that return values are described while missing an output schema, and the as_of parameter is never referenced in prose.

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 and their YYYY-MM-DD format and default-today behavior are already documented in the schema. The description does not mention as_of at all, adding no meaning beyond the structured fields — baseline 3 is appropriate.

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 specific verb and resource ('Exact age from a birth date') and enumerates the returned components (years, months, days, total days, days to next birthday). It does not explicitly distinguish itself from the sibling date_difference, but the tool's purpose is unambiguous.

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 the birth-date framing, which makes the intended context clear. However, there is no explicit guidance on when to prefer this over date_difference, nor any note on the as_of parameter's role in backdating an age calculation.

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