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

The annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description adds genuine value beyond that by disclosing a cost of 1 credit and noting the result includes 'comprehensive pregnancy timeline information', but it says nothing about precision, edge cases, or how the two date inputs interact.

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 sentence plus a cost note, front-loaded with the purpose and immediately followed by the two input methods. The only waste is the redundant restatement of the tool name at the start, which is minor and conventional.

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?

This is a simple two-parameter read-only calculator with a full output schema, so the description need not explain return values, and it gestures at the timeline output anyway. The remaining gap is the lack of any guidance on parameter precedence when both dates are provided.

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%, so the baseline is 3, and the description earns an increment by stating that the two parameters are alternatives ('using either last menstrual period or conception date') — a one-of relationship the schema itself does not encode, since both properties are optional and no oneOf is declared. It does not clarify what happens if both or neither are supplied, which keeps it from a 5.

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 names a specific verb and resource ('estimates pregnancy due dates') and states the two supported input methods (last menstrual period or conception date), which separates it from generic siblings like DateCalculator or AgeCalculator. It does not explicitly name the closer siblings OvulationCalculator or MenstrualCycleCalculator, so differentiation is left partly to inference.

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 context is implied by naming the two calculation methods, so an agent can infer the tool applies to pregnancy due-date estimation. There is no explicit when-to-use versus when-not guidance, and no mention of when OvulationCalculator or MenstrualCycleCalculator would be the better pick.

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