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

Annotations already cover the safety profile (readOnly, idempotent, openWorld, non-destructive), so the bar is lower, yet the description adds genuinely useful behavior: OAuth is required, it will never guess missing required measurements, and explicit inputs take precedence over saved ones. It does not describe failure modes beyond that (e.g., what happens when no route is verified).

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?

Four tight sentences, front-loaded with the login requirement and the saved-vessel behavior, then units, then return shape. The terse unit list is compact rather than padded, though the return-metadata sentence is thin given there is no output schema.

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 nested 11-property routing request with no output schema, the description covers auth, defaults/precedence, no-guessing, units and bearing convention, and notes that source/freshness metadata comes back. The main gap is that the response payload itself is only gestured at, not characterized.

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 effectively 0% for the nested measurement fields, and the description compensates with the single most important missing semantics: units (ft, kt, s, F, mi) and the 'directions FROM' convention. That is exactly the information the schema omits, though per-field ranges and the via/corridor specifics still live only in the schema.

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+resource (route planning) and pins the resource's scope: routing with your saved vessel parameters as defaults. That implicitly contrasts with the sibling plan_route, but the description never names or describes the alternative, so the agent must infer the split from the title alone.

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?

Gives prerequisites (requires OAuth login) and a precedence rule (explicit measurements override saved values), which is real usage guidance. However, it never says when to pick this over plan_route, the most obvious alternative, leaving the primary routing decision to inference.

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