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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is fully covered by structured fields. The description adds only 'Returns delta in multiple units,' which is thin but not contradictory; it discloses nothing about rounding, sign convention, or boundary handling.

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?

Front-loaded with the core action, but it runs four sentences where two would do, and one of them ('See list_bundles for related voyage calculators') carries no actionable information. Structure is acceptable; content economy is not.

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-required-parameter tool, the description never mentions the only inputs the schema accepts (cities) and instead describes a different signature entirely. An agent reading only the description would pass the wrong arguments; the presence of an output schema excuses only the return-value explanation.

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?

The description asserts 'Inputs: start datetime, end datetime,' but the schema requires city1 and city2, both enums of ten city names, with additionalProperties false. This does not merely under-document the two parameters (whose schema coverage is 100%) — it actively misdescribes them, which is worse than silence.

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 ('Compute the difference') and resource ('two times or dates') with the output units enumerated, which is reasonably clear in isolation. However, the stated resource does not match the tool's actual inputs (cities), and it does nothing to separate itself from close siblings like calculate_days_between, calculate_age_in_units, or calculate_time_zone_difference.

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?

'Use for project tracking, age, or scheduling' gestures at contexts but gives no criteria for choosing this over the many sibling calculators that cover the same ground (calculate_days_between, calculate_age, calculate_time_zone_difference). The trailing pointer to 'list_bundles for related voyage calculators' is irrelevant noise rather than routing guidance.

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