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

The annotations already mark this as readOnly, idempotent, open-world and non-destructive, and the description adds real information beyond them. It discloses the credit cost (1 per event), the plan gating, the maximum 30-day lookback, the 400-square-degree box cap and the default 24-hour window. These are non-obvious constraints that an agent cannot infer from the structured fields.

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?

The description is dense but organized: the event kinds come first, then the geographic option, then the time limits, then the cost and plan. Every clause carries information, and there is no filler. The trailing 'and more' and the URL slightly loosen it but do not waste space.

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 7-parameter, zero-required read tool with no output schema, the description covers the content, the defaults, the hard limits and the access requirements. The one missing piece is a description of what an event record contains, but the annotations and the event-kind list largely make up for it. Overall the description is nearly complete for the complexity involved.

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?

With a schema description coverage of 100%, the schema already documents every parameter, so a baseline of 3 applies. The description still improves on this by telling the agent which kinds are returned by default and what the implicit defaults are for the 'since' window and for the latitude/longitude box. It does not explain the ISO 8601 format or how the box coordinates interact beyond schema descriptions, which keeps it at 4.

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 uses a specific verb-and-resource phrase and an enumerated content list: 'Recent events from AIS: arrivals, departures, anchoring, weighing anchor and approaches by default' plus additional kinds. An agent immediately knows this is a query of AIS port events and what is in them. Siblings such as port_now, vessel_activity and port_calls_on_date are never named or differentiated, so it falls short of a 5.

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?

The description gives clear operating context: a box is optional and may be at most 400 square degrees, 'since' defaults to 24 hours and may go back at most 30 days, and the call requires a paid plan. What it does not say is when to prefer this tool over port_now, vessel_activity or port_calls_on_date, and that absence of explicit routing keeps it below a 5.

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