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

Annotations already declare read-only, non-destructive, and open-world semantics. The description adds valuable detail beyond those annotations: only successfully found vessels are returned, the response includes a found count, and result fields match get_vessel. This tells the agent how partially matched batches are handled.

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 sentences: purpose and limit, return behavior, and usage direction. Front-loaded with the core action; no filler and no repetition of schema details.

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?

With annotations covering safety and an output schema present, the description covers the essential runtime behaviors: accepted inputs, total identifier cap, partial-result handling, and the single-vessel alternative. Nothing an agent needs to decide or call correctly is missing.

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 schema documents each parameter with format constraints (7-digit IMO, 9-digit MMSI, UUID), but the description adds the cardinality and mixing rule — any combination of MMSI, IMO, and UUID lists with a combined cap of 100 identifiers — which is absent from the schema. This is meaningful added value.

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?

States a specific verb ('Return'), the resource ('current position and basic information for many vessels'), and the input mix ('MMSI, IMO and UUID lists, up to 100 identifiers'). It also distinguishes itself from get_vessel by naming the single-vessel alternative, so an agent can tell them apart immediately.

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?

Explicitly says to use this tool 'instead of many get_vessel calls' when looking up a known set and 'for a single vessel use get_vessel.' That clear when-to-use/when-not-to-use guidance is exactly what an agent needs to choose correctly among siblings.

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