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

The description adds useful behavior beyond the annotations: results are sorted nearest first, each includes distance and bearing, and the center vessel is excluded when using mmsi. The read-only and idempotent hints are already in the annotations, so the description does not need to restate them.

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?

Two sentences, zero filler: the first states the core behavior and result shape, the second gives direct usage intent. Every clause earns its place.

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 read-only spatial query, the description combined with the 100%-covered schema, annotations, and output schema is complete. It covers the center modes, radius constraints, result ordering, and distance/bearing output without needing to re-explain every parameter.

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% and every parameter already has a clear description. The description mostly summarizes what the schema states, such as default and maximum radius and the choice between lat/lon and mmsi, without adding substantial new parameter-level detail.

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 states a specific verb and resource: finding vessels within a radius of either a point or another vessel. It also distinguishes this from the sibling area-based lookup by emphasizing 'radius' and by naming the two center modes (position or vessel).

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 explicitly tells the agent when to use the tool: 'Use for what is near this position or what is around vessel X.' However, it does not mention when not to use it or name alternatives such as find_vessels_in_area for area searches, so it stops short of full exclusion guidance.

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