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

With no annotations, the description carries the full burden and does disclose genuinely useful operating context: the computation is stateless, the reference date defaults to today in UTC (adding the timezone the schema omits), and the call is paid via x402 at $0.01 USDC on eip155:8453 — a cost/payment disclosure an agent must know before invoking. It does not cover error behavior for malformed or future dates, which keeps it out of the top band.

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?

Three short sentences, front-loaded with the computation and its output, with the payment note last. The middle 'Use this when...' sentence is redundant with the opening and contains a grammatical slip ('needs to exact age'), a small amount of waste in an otherwise tight definition.

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 correctly compensates by specifying the return shape (years/months/days plus total days lived). Combined with the default-date and pricing details, an agent has what it needs to call the tool; only input-validation/error semantics for invalid dates are 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% for both parameters, so the baseline is 3. The description restates the default reference date ('defaults to today (UTC)') and the semantic role of 'birth', adding only the UTC qualifier beyond what the schema already documents.

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 names a specific verb and resource ('Calculate a person's exact age... from their date of birth') and even enumerates the output units (calendar years, months, days, total days lived). It is unambiguous on its own, but it never differentiates itself from the nearest sibling, calculators_date_difference_calculator, which an agent could easily mistake for the same computation.

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?

'Use this when an agent needs to exact age in years, months and days' is essentially a restatement of the purpose sentence rather than new routing guidance. There is no when-not condition and no mention of the alternative (date_difference_calculator) for non-person date spans, so usage is only implied.

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