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

Annotations already declare readOnly, idempotent, non-destructive, and openWorld=false. The description adds behavioral context by specifying the output components and a month-end convention, which is useful beyond the annotations, though the convention itself is not concretely defined.

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?

Two sentences, front-loaded with the core calculation and followed by essential input guidance. No redundant or wasted language.

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?

Given the low complexity, rich input schema, present output schema, and informative annotations, the description is nearly complete. It could clarify parameter ordering and the exact month-end convention, but the required information for correct invocation is largely present.

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 the schema already documents both date parameters. The description adds 'birth dates' and mentions month-end handling, but it does not name or further explain date1/date2 semantics, so the baseline of 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: calculating years, months, days, and total days between two birth dates. This clearly identifies the operation, though it does not explicitly distinguish itself from sibling tools like date_calculator.

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?

The description gives input guidance ('Use explicit Gregorian dates and a stated month-end convention') but does not say when to choose this tool over alternatives such as date_calculator. Usage is implied from the age-difference context, not explicitly scoped.

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