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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=true, so the safety profile is covered. The description adds one genuinely useful behavioral fact not in the annotations: the call costs 1 credit. It does not mention that outputs are statistical estimates rather than medical predictions, nor any assumptions baked into the phase 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?

The single functional sentence is well-formed and front-loads the capability, but the tool name 'Ovulation Calculator' is repeated redundantly before it (already present as name and title), wasting the opening. The credit cost is correctly appended at the end and is terse.

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 two-parameter, read-only calculation tool with full schema coverage, an output schema that documents return values, and annotations covering the safety profile, the description carries enough to call it correctly. The remaining gap is routing against overlapping cycle-related siblings.

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 both parameters (last_period as YYYY-MM-DD and cycle_length defaulting to 28) are already fully documented with examples and defaults. The phrase 'based on menstrual cycle data' restates the schema rather than adding syntax or edge-case meaning, 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?

The description uses a specific verb ('estimates') with named outputs ('ovulation dates, fertile windows, and detailed cycle phase information') and a named input ('menstrual cycle data'), so an agent knows exactly what it computes. It does not, however, distinguish itself from the sibling MenstrualCycleCalculator or DueDateCalculator, which overlap substantially in scope.

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?

There is no guidance on when to pick this over MenstrualCycleCalculator or DueDateCalculator, nor any stated preconditions (e.g., whether last_period must be in the past, or whether the tool is for conception planning vs. general tracking). Usage must be inferred entirely from the tool name and the word 'ovulation'.

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