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

Annotations already cover safety (readOnlyHint, idempotentHint, destructiveHint false), and the description adds substantial extra behavior: live vessels ordered before out-of-range ones with positions up to 7 days old (age_s), the compact row shape, and the policy that private craft are never returned while area/nearby results roll them into a private_vessels count. That is unusually rich disclosure for a search tool.

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 lookup keys, then result ordering, then row shape, then exclusions — a sensible priority order. It is a long single block of text, but nearly every clause carries distinct information; only the parenthetical row-field list is slightly list-heavy.

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 does the work of enumerating the returned fields and the ordering semantics, and it covers the private-vessel edge case that would otherwise surprise an agent. Gaps remain around the limit parameter and whether results are truncated when the query matches many ships.

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 50%: query is documented in both places, but limit (default 10, max 20) is never mentioned in the description, so the cap and default behavior are left entirely to the schema. The description restates the query format (name part, 9-digit MMSI, 7-digit IMO) rather than adding new syntax guidance, so this lands at the baseline for partial coverage.

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?

Specific verb (find) plus resource (ships) and the three lookup keys (name/partial name, 9-digit MMSI, 7-digit IMO). It explicitly routes to get_vessel for full details, which cleanly separates it from the sibling that returns one full record.

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 states what the tool is for and names the alternative (get_vessel) for the full-detail case, and it declares the exclusion rule for private vessels. It never contrasts itself with the other discovery siblings (vessels_in_area, vessels_near, vessel_track), so the agent must infer that geospatial lookup belongs elsewhere.

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