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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint, so the description earns credit for going further: it discloses AIS reception gaps ('no receiver heard her'), a data-redaction caveat ('a position only where we may pass it on'), per-call credit cost, and plan-gated history windows. It does not describe the response shape or any result limits, which matters since there is no output schema.

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 payload (where, when, gaps, events) before cost and plan constraints, and the parentheticals carry useful caveats rather than filler. The first sentence is dense and slightly tangled, but nothing is wasted.

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?

Given two simple parameters, no output schema, and rich annotations, the definition covers what is missing elsewhere: cost, entitlement, and historical depth. The remaining gap is the return shape — whether calls are paginated, how events are attached, and what an empty result means — which the agent must discover by calling.

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%, so the baseline is 3, but the description adds real meaning the schema cannot: the 365 maximum is not universally available, it is 90 days on Plus and 365 on Pro/Scale. It also restates the default of 7 days in context of what is being windowed.

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 names a specific resource and scope: a single vessel's port calls, with arrival/departure times, reception gaps, and en route events. That implicitly separates it from port-centric siblings like port_calls_on_date and from vessel_track/vessel_activity, but it never states the distinction explicitly, so an agent must infer the boundary.

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?

Prerequisites are unusually well covered (paid plan required, plan-tiered history limits, 1 credit per call), which tells the agent when the tool is even callable. What is missing is positive routing guidance: no sentence says to use this instead of port_calls_on_date or vessel_track, so the choice among siblings is left to inference.

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