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

Annotations already declare readOnlyHint=true/openWorldHint=true, so the safety profile is covered. The description adds genuinely useful behavior beyond that: Garmin's 91-day cap, the 92+ inclusive-day rejection rule, and the important fact that the limit is NOT enforced here, making it the caller's responsibility. It stops short of saying anything about the returned payload.

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 resource and range, followed by the operational constraint. The parenthetical 'not enforced here (caller's responsibility)' is dense but earns its place by preventing a false assumption of validation.

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 read-only tool with full parameter coverage and no output schema, the description supplies the one non-obvious operational fact (the 91-day limit and its non-enforcement). It could say more about what the calendar data contains (entries vs. predictions), but nothing required to invoke it correctly is missing.

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% and both parameters already document the YYYY-MM-DD (UTC) format. The description adds only the inclusive-window constraint tied to those two dates, which is relevant but does not go beyond what the schema already conveys about the arguments themselves.

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 resource ('Menstrual-cycle calendar data') and a specific scope ('between two dates'), which an agent can distinguish from date-scoped siblings like get_menstrual_data_for_date or summary-style tools like get_menstrual_cycle_summary. It never names those siblings, so differentiation is inferred rather than stated.

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 two-date framing implies when the tool applies (range queries), but there is no explicit guidance on when to choose it over get_menstrual_data_for_date, get_menstrual_cycle_summary, or get_menstrual_reports, nor any stated prerequisite such as menstrual-cycle setup. Usage is only suggested.

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