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

Annotations already declare readOnlyHint, idempotentHint and closed-world behavior, so safety is covered. The description adds genuine output scope ('dates mapped out for your next four cycles', six-day fertile window), which is useful since no output schema exists, but it discloses nothing further about assumptions or edge cases.

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?

One tight, front-loaded sentence that leads with the deliverable and then the inputs. The trailing web page URL is mildly extraneous but standard and harmless.

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 three-parameter calculator with fully documented schema and no output schema, the description covers what is computed and how far ahead. Nothing an agent needs to invoke it correctly appears to be 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 description coverage is 100% with defaults and ranges documented for date, cycle and luteal. The description only restates the period and cycle-length inputs and omits the luteal phase entirely, so it adds little beyond the schema. 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 (pinpoint) and resource (ovulation day and six-day fertile window) with scope (next four cycles). The resource is naturally distinct from the closest siblings period_calculator and pregnancy_due_date_calculator, but the description never names or contrasts them explicitly.

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 described inputs ('from your last period and cycle length'), so an agent can infer applicability. However there is no explicit when-to-use guidance, no exclusion of similar date/pregnancy tools, and no stated prerequisites.

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