vessels_in_area

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

With no annotations, the description carries the behavioral burden and discloses key traits: it filters already-collected data, is independent of current subscriptions, retains vessels until they age out after a region is switched away, and returns nothing for unsubscribed areas. This goes beyond a generic read and helps an agent predict empty or stale results.

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 front-loaded with its core purpose, and each following sentence earns its place by explaining rationale and edge cases. It is slightly longer than strictly necessary, but there is no fluff or repetition.

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 tool with zero required parameters and an output schema, the description covers purpose, selection rationale, and an important behavioral edge case (empty results for unsubscribed areas). It appropriately relies on the schema for parameter syntax and on the output schema for return shape; the only gap is explicit naming of competing siblings.

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?

All three parameters have complete descriptions in the schema: bbox format is given as 'south,west,north,east', region has a 'malaysia' example and points to list_regions, and limit documents bounds and truncation visibility. The description adds conceptual 'area' context but no additional parameter-level semantics.

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 'Vessels inside one area of sea, rather than everywhere the server watches,' which clearly identifies the resource and scope. It also distinguishes the tool from the subscription question ('a different question from what is subscribed to') and explains why a caller would pick it, though it never names a sibling tool explicitly or uses a crisp action verb.

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 explains when this tool is appropriate: 'This exists because a selection covering several regions can hold far more vessels than any one caller wants at once.' It also gives direct guidance ('Ask for the water you care about') and clarifies a boundary case: 'an area nobody is subscribed to simply returns nothing.' It does not explicitly enumerate alternative sibling tools.

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