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

Annotations already cover the safety profile (readOnly, idempotent, non-open-world), so the bar is lower. The description adds genuine behavioral context beyond them: the underlying 280-day rule, that cycle length shifts the result, the supported alternate bases, and that output includes weeks pregnant as of today.

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-load the core rule, then the alternate methods, with no filler in the body. The trailing URL is mildly promotional and adds no invocation value, which keeps it from a 5.

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 calculator with zero required parameters, full schema coverage, and no output schema, the description's coverage of the calculation rule and alternate inputs is close to sufficient. A brief note on what the result contains beyond 'weeks pregnant today' would close the remaining gap.

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 all three parameters (date, cycle, method) are already documented, establishing a baseline of 3. The description restates the calculation logic that gives those parameters meaning but adds no format, range, or edge-case detail beyond the schema.

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 states a specific computation (due date 280 days from the last period, adjusted for cycle length) and names the alternate input bases (conception, IVF transfer), so the resource is unmistakable. It does not explicitly differentiate itself from adjacent siblings like ovulation_calculator or period_calculator, which keeps it short of a 5.

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 domain (pregnancy due dating) and the alternate methods hint at which input basis to pick, but there is no explicit when-to-use vs when-to-use-another-tool guidance (e.g., versus ovulation_calculator or period_calculator). The method choice itself is documented in the schema enum, not the description.

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