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

Beyond the readOnly/idempotent annotations, the description discloses result ordering (live ships first, then out-of-range with last known position up to 7 days) and a privacy rule excluding private vessels/Class B without IMO, with a private_vessels count reported in other tools. These are non-obvious behavioral traits an agent could not infer from 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 search capability and identifiers, then the return-row contract, then the sibling pointer. It is dense but every clause carries information; the long field enumeration is the only mildly heavy element.

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 fully carries the return contract: exact compact row fields include mmsi, name, flag ISO code derivation, speed/course units, age_s, status, source. Combined with the ordering and privacy rules, an agent has everything needed to interpret results.

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 100%, so both parameters are already documented. The description adds only marginal meaning—confirming partial-name matching, which the schema does not state—but says nothing about the limit parameter or its 1–20 cap. Baseline 3 is appropriate.

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 opens with a specific verb and resource ('Find ships') and names the exact identifier types accepted (name fragment, 9-digit MMSI, 7-digit IMO). It also explicitly routes detail lookups to a named sibling ('call get_vessel for full details'), distinguishing it from the broader lookup/nearby/area tools.

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 clearly implies the right context (identifier-based lookup) and names the alternative for full records ('call get_vessel'). It does not explicitly exclude the other search-like siblings (lookup_vessels, vessels_near), so the agent must infer when identifier search beats area search.

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