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

Annotations already cover read-only/idempotent/non-destructive, and the description goes considerably further: a 30-per-minute rate limit, a 10-credit cost, and a specific entitlement requirement (Data API Plus/Pro/Scale or a paid Watch plan) with a pricing link. It also discloses the important limitation that it "finds what our charts and data show, never everything," which is exactly the caveat an agent needs before presenting results as authoritative.

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 front-loaded sentences with no filler: capability first, scope disclaimer second, operational constraints last. The final sentence is dense with cost/entitlement details but each element is actionable; slightly tighter structuring of the limits would make it a 5.

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 7-parameter read-only tool with no output schema and already-rich annotations, the description covers purpose, scope limits, cost, and rate limits well. The remaining gap is behavioral on omission — whether a missing draught or beam silently disables the corresponding check — and slightly more detail on the warning output.

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 description coverage is 100%, so the baseline is 3, and the description adds only a partial interpretive note that "depth" means her draught plus under-keel clearance — a useful linkage between two of the seven parameters. Beam, length, and air draught carry no explanation of how they influence the check, and nothing says what happens if a hull parameter is omitted.

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?

A specific verb plus resource ("Check a planned route leg by leg") immediately followed by the exact criteria checked — land, depth, sea room, traffic separation schemes — and the output shape ("plain-language warnings"). This is clearly distinguishable from the sibling plan_route, which creates rather than checks a route.

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 phrase "a planned route" implies this runs after a route exists, and "not for navigation / a planning aid" sets scope boundaries. But there is no explicit routing to alternatives (e.g. "use plan_route first to create the route") and no statement of when to skip this check, so the guidance is implied rather than stated.

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