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

Adds substantial context beyond the annotations: per-call pricing via x402 USDC or card key, 25 free calls, failed calls free, and the explicit note that repeats are not free — which explains the idempotentHint=false flag that would otherwise look odd for a pure computation. It also confirms read-only behavior ('reads or computes only and changes nothing') and states the UTC default, consistent with readOnlyHint and destructiveHint=false.

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?

Outputs are front-loaded in the opening clause, followed by usage, example, and cost/repeatability caveats. Every sentence carries information an agent needs (what it returns, when to use it, input format, billing behavior); nothing is padding.

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 no output schema, the description fully specifies the return shape (all derived values), the measurement-date default and override, and the pricing/caching behavior that governs repeated calls. An agent could invoke this correctly and predict its output without opening any other field.

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 100%, so the baseline is 3; the description adds value by clarifying that measurement defaults to today in UTC 'or on any date you give' and supplies an example value (birthdate=1990-05-17). It does not restate per-parameter syntax beyond that, so it lands just above baseline.

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?

Names a specific computation (exact age from a date of birth) and enumerates the outputs: years/months/days, total days lived, weekday of birth, and next-birthday date/countdown. This is specific enough to be told apart from generic date siblings like date_diff or date_info, and the required input (birthdate) is stated up front.

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 concrete usage contexts ('age checks, forms and anniversaries') plus a worked example, so an agent knows when the tool fits. It stops short of naming an alternative or an exclusion (e.g., use date_diff for arbitrary date spans), which keeps it at 4 rather than 5.

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