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

Beyond the readOnly/idempotent annotations, it discloses the 1-hour observation window, the 5° box-size limit, sort order, and a privacy rule with an observable side effect (private vessels never listed, counted in private_vessels). These are behavior traits an agent could not infer from the 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 purpose, scope and ordering before the result-row inventory and the get_vessel pointer. The embedded field list is dense but earns its place given there is no output schema.

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?

With no output schema, the description carries the return-shape burden and does so by listing result-row fields, and it explains exclusion semantics. It omits pagination/limit behavior and the meaning of the ship_type categories, which are minor residual gaps.

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 low (17%), but the description clarifies the geographic parameters by stating the box constraint ('at most 5° on each side'), which is not in the schema. It says nothing about limit semantics or the ship_type filter, so it only partially compensates.

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 verb and resource ('Ships heard in the last hour inside a box'), plus scope (last hour, max 5° per side) and ordering (largest first). It is clearly distinguishable from siblings like vessels_near and search_vessels without opening any schema.

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?

It explicitly routes deep-dive calls to get_vessel ('call get_vessel for full details of one ship'), which is real alternative guidance. It does not, however, explain when to prefer this tool over vessels_near or search_vessels, so the guidance is clear but not exhaustive.

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