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

Annotations already establish readOnly, idempotent, non-destructive and closed-world behavior, so the bar is lower; the description adds genuinely useful behavioral context beyond them. It discloses the no-argument default (returns the full catalog), the returned slug per vessel, and the filter interaction rule ('Ignored when vessel is given'). Only the result shape/paging conventions are left to the output schema.

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: the coverage list comes first, the usage trigger second, the invocation/default behavior last. Every clause carries information an agent needs, and the most load-bearing content is front-loaded.

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 an output schema present, return-value detail is not required. The description covers both calling modes (list vs. single-vessel lookup), the filter interaction, and accepted identifier formats, so an agent can call it correctly on the first try.

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%, so the baseline is 3, but the description adds semantics the schema does not fully carry: calling with no arguments lists the entire catalog, and the optional mode filter is explicitly subordinate to vessel. It also illustrates accepted vessel identifier forms ('20ft-container', '20 foot container', '40HC'), reinforcing the schema rather than merely restating it.

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 the exact resource (interior dimensions, volume, floor area, payload) and scopes it precisely to 47 shipping containers, truck trailers, rail wagons and air ULDs, enumerating concrete examples (20ft, 40HC, reefer, LD-3, PMC). The catalog-listing verb ('lists the whole catalog') makes it unmistakably a reference lookup rather than a calculation, which separates it from the calculate_cbm / how_many_pallets_fit / plan_cargo_load siblings.

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 an explicit trigger list ('Use this when someone asks for the internal or interior dimensions, cubic capacity, floor area, payload or weight limit'), which is clear when-to-use guidance. It does not, however, name an alternative tool or state when not to use it versus the calculator siblings, so it falls short of the top score.

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