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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description adds genuinely useful behavior beyond that: the exact set of computed outputs and a cost disclosure (1 credit), which matters for a metered tool. It does not mention that results depend on the current date at call time, though the countdown-to-birthday line hints at it.

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 dense sentence plus a parenthetical cost note, front-loaded with the purpose before the output enumeration. Minor waste from repeating the tool name twice at the start ('Age Calculator: Age Calculator converts...'), but otherwise tight.

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 only two parameters, full schema coverage, an output schema and explicit annotations, the description says enough for correct invocation. The only substantive gap is the implicit dependency on the current date/timezone for the 'today' calculation, which an agent might otherwise miss.

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%, with dob format (YYYY-MM-DD) and the IANA timezone default already documented in the schema, so baseline 3 applies. The description adds no extra meaning about the two parameters — notably it never explains that the timezone also determines what 'today' means for the countdown, which would have been a value-add.

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 and resource: converting a date of birth into exact age, with an explicit enumeration of the breakdown units (years, months, weeks, days, hours, minutes, seconds), word form and next-birthday countdown. It does not differentiate itself from adjacent date tools such as DateCalculator, DueDateCalculator, or WorkingDays, but the intent is unmistakable.

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 only implied by the purpose statement — there is no explicit 'use this when' clause and no mention of when a sibling date tool would be a better fit. The one implicit signal is that it accepts a birth date rather than two arbitrary dates, which helps route the agent, but the guidance is left to inference.

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