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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld=false), and the description adds genuinely non-structured behavior: a one-hour recency window, a hard 50 nm radius cap, nearest-first ordering, the exact compact row fields returned, and the private-vessel exclusion policy with the private_vessels omission count.

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 dense sentences, front-loaded with the core behavior (recency, radius, ordering) before the row shape and the private-vessel caveat. The field enumeration is long but earns its place by describing the return payload absent an 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?

For a parameterized read tool with no output schema and sparse schema descriptions, the description supplies the filtering semantics, ordering, return fields, and privacy policy. Nothing an agent needs to call and interpret this correctly is missing.

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 only 20% (mmsi is the sole documented param), so the description must compensate. It clarifies the two mutually exclusive centering modes (point via lat/lon vs another ship via mmsi) and restates the radius bound, though it never explains limit or the default radius of 5 nm.

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/resource ('Ships heard in the last hour within a radius ... of a point or of another ship') plus scope (50 nm cap), ordering (nearest first), and a named sibling for a different task (get_vessel). An agent can distinguish this from vessels_in_area/search_vessels by the radius-of-point/ship framing.

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: 'call get_vessel for full details of one ship,' and the radius framing implies the nearby-lookup use case. It stops short of contrasting with siblings like vessels_in_area (area vs radius) or search_vessels, so no exclusions are stated.

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