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 non-obvious behavior: the reference date defaults to today in UTC, and the call is metered at $0.001/call via x402 (USDC, eip155:8453). That pricing and timezone-default context is real behavioral value not found in the schema. It does not state that the operation is a side-effect-free computation or how invalid/future dates are handled.

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?

Core capability is front-loaded in the first clause and the trailing sentence is a single compact fragment carrying the default date and price. Both parts earn their place, though the em-dash price append reads slightly as tacked-on rather than integrated.

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 computation with no output schema and no annotations, the description supplies what is needed: the inputs, the output units, the default reference date, and the cost. Missing only edge-case behavior (invalid or future dates) and the exact return shape, which are minor for this tool.

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% with only two simple parameters, so the schema already documents both 'birth' and 'on' including the YYYY-MM-DD format and the today default. The description echoes the default-date behavior but adds no format or edge-case semantics beyond what the schema provides, so 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?

States a specific verb and resource ('Calculate a person's exact age ... from their date of birth') and enumerates the output units plus total days lived, so the agent knows precisely what comes back. It never names or contrasts with the closest sibling, calculators_date_difference_calculator, so it stops short of full sibling differentiation.

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 phrasing rather than stated: the agent can infer this is for age-from-DOB rather than general date arithmetic, and the 'defaults to today (UTC)' note clarifies the common case. There is no explicit when-to-use/when-not-to-use guidance or pointer to the date_difference sibling that handles overlapping territory.

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