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

Annotations already declare readOnly and idempotent, so no contradiction exists and the safety burden is lifted. The description adds useful behavioral context: it reports a live snapshot ('right now'), includes freshness, and describes what the bbox versus station modes return, which goes beyond the 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?

Three dense sentences with no filler, and the key purpose is stated first. The actionable usage rule is front-loaded near the end of the description, making it easy to scan while keeping the main semantics up front.

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?

Despite its small size, the definition fully covers what the tool does, what inputs it accepts, what kind of information the caller should expect, and when it should be invoked. With an output schema present and only two optional parameters, nothing essential is missing for an agent to use it correctly.

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 the parameters are already well documented in the schema. The description reinforces the split between bbox and station modes but does not add substantial meaning beyond what the structured descriptions already provide.

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 verb and resource: reporting where AIS is currently being heard, plus sources, stations, freshness, and vessel counts. It clearly distinguishes this from the vessel-search siblings by focusing on coverage infrastructure rather than finding individual vessels.

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 gives explicit call patterns: pass a bounding box for station coverage and vessel counts, or a station id for station-level numbers. The closing instruction to call it before claiming a region has no traffic provides strong contextual guidance, though it does not explicitly name sibling alternatives to exclude.

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