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

Annotations already declare the safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is lower. The description adds that a next_period value is also produced, useful context beyond ovulation, but says nothing about precision caveats or assumptions of the calculation.

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 tight sentences, front-loaded with the purpose. The 'Returns:' enumeration mildly duplicates the output schema, but otherwise every phrase earns its place.

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 an output schema present, the description needn't enumerate return fields, yet it does so and covers inputs, so an agent has enough to invoke it correctly. The missing piece is differentiation from related cycle/due-date calculators, a minor gap for a self-contained math 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 description coverage is 100%, so the schema already documents last_period_date (YYYY-MM-DD) and cycle_length (21-45, default 28). The description merely restates 'from last period and cycle length' without adding validation limits or format detail beyond the schema, so the baseline of 3 applies.

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+resource (calculate ovulation date and fertile window) plus the inputs it derives them from (last period, cycle length). It does not, however, distinguish itself from near-siblings like calculate_menstrual_cycle or calculate_due_date, leaving overlap ambiguity.

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 never says when to use this tool versus alternatives such as calculate_menstrual_cycle or calculate_pregnancy_due_date. The only routing hint is a vague pointer to list_bundles for 'related sante calculators,' which does not tell the agent when this specific tool is the right choice.

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