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

Annotations already declare readOnlyHint=true, idempotentHint=true and destructiveHint=false, so safety is covered. The description adds two useful behavioral facts beyond the annotations: it requires the last period start (within 120 days) and it discloses that when `period_may_be_late` is true the returned say line warns of a late period and suggests seeing a doctor. It does not describe the broader output shape or phase naming.

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?

Purpose and use cases are front-loaded, then constraints, then the safety boundary — a sensible order. Slightly repetitive wording (pregnancy/contraception appears twice in one sentence) and the opening restates the title, but nothing is wasted enough to impede scanning.

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 carries the return-value burden and does disclose the key say-line behavior around a late period, plus the medical guardrail. It is complete enough to call correctly, though it never sketches the rest of the response (phase name, workout/food payload).

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 tz, country, diet, cycle_length, period_length and the last_period_start alias are already fully documented in the schema. The description only restates the required last-period input and mentions period_may_be_late, which is actually a return value rather than a parameter, so it adds essentially no new parameter meaning.

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 concrete deliverable — the user's current cycle phase plus workout and food ideas — and scopes it to 'today', which separates it from the week-ahead sibling. The sample queries ('what phase am I in', 'what should I train today?') make the purpose unambiguous to an agent.

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?

Explicit triggers are given ('what phase they are in', 'what workout or food suits them today', 'why their energy is up or down') with two concrete example utterances. It also states when NOT to use it (fertility, ovulation timing, contraception, pregnancy planning) and gives the fallback action (refer to doctor or pharmacist).

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