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

The description discloses the critical regional coverage limitation ('COVERAGE IS REGIONAL... Points elsewhere in the world return nothing') and describes raw data freshness, building on the readOnlyHint and openWorldHint annotations. This adds substantive behavioral context beyond what annotations provide.

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 a single dense paragraph but front-loads purpose, then output fields, usage examples, and coverage. No filler or repetition; every sentence adds value.

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 lacking an output schema, the description enumerates all returned per-ship fields and covers edge cases (points outside coverage return nothing). Combined with the detailed parameter schema and read-only annotations, this provides sufficient context for correct use.

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?

The input schema already describes all five parameters with high coverage (100%). The description contributes usage examples (Helsinki coordinates, vessel_type filter) and clarifies the meaning of vessel_type, but these are supplementary to the schema, so the baseline of 3 applies.

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 clearly states the tool returns live vessel positions near a point, and enumerates the returned fields (MMSI, name, type, speed, etc.). This specific scope distinguishes it from siblings like ais_area_count (counts) and ais_vessel (single vessel detail).

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 provides explicit example queries ('what ships are near Helsinki', 'vessel traffic outside Turku') and notes regional coverage, guiding when to use it. However, it does not name alternatives or explicitly say when not to use it, so it lacks explicit exclusions.

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