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

Annotations already cover the safe-read profile (readOnly, idempotent, non-destructive), and the description adds substantive behavior beyond them: a one-hour recency window, a maximum 5° box, largest-first ordering, and the non-obvious policy that private vessels are never returned but are counted in a private_vessels field. That exclusion rule is the kind of hidden behavior an agent could not infer from schema or annotations.

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 scope, constraint and ordering before the detail list, with zero filler. The compact row field enumeration is long but justified because there is no output schema; it could still be tightened slightly.

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 six-parameter read tool with no output schema, the description supplies the return shape, the recency semantics, the bounding-box limit, the ranking, the private-vessel exclusion with its counter, and the escalation path to get_vessel. Only the failure mode for an oversized box is unstated, which is a minor 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 coverage is 100%, giving a baseline of 3, but the description contributes meaning the schema lacks: the 5° per-side cap on min/max lat/lon and the 'largest first' implication for the limit parameter. Only ship_type is left unmentioned.

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 resource (ships), a precise scope (heard in the last hour inside a bounding box), a hard constraint (box at most 5° per side) and an ordering (largest first). This clearly separates it from the radius-based vessels_near and the name-based lookup_vessels/search_vessels siblings.

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?

Explicitly routes the agent to get_vessel when full detail on a single ship is needed, and the box-size cap tells the agent this tool is not usable for wide-area queries. It never names a competing sibling (e.g. vessels_near for radius searches) or states exclusions, so it falls short of a full when/when-not map.

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