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

Annotations already cover safety (readOnlyHint=true, openWorldHint=false), so the description's job is to add semantics — and it does, explaining that one_way: true means the boat is handed back elsewhere and otherwise the loop returns to the start port, plus that overnight stops are ordered. It does not disclose volume, pagination, or caching behavior, which keeps it off a 5.

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?

Front-loaded with the resource and then a single dense sentence listing fields, ending with the sibling pointer where an agent will look for it. Every clause is informative, though the field enumeration partly duplicates the output schema and could be trimmed.

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 values need no prose explanation, and annotations cover the safety profile. What remains — record semantics (one_way, loop closure, stop ordering) and the get_route branch — is exactly what an agent needs and is present.

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% with both parameters fully described (lang enum, country enum, and 'omit for all routes'), so the schema carries this dimension. The description adds only an oblique hint of base scoping ('from a charter base') and never mentions language selection. Baseline 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?

States a specific resource (sailing routes from a charter base) with scope (a few days to two weeks) and enumerates the shape of each record. It explicitly separates itself from get_route, which covers the day-by-day plan, so an agent can pick between them without opening a schema.

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?

Names the sibling alternative (get_route) and the condition that selects it. It does not state exclusions in the other direction (when list_routes is the wrong call), but the routing is clear enough for confident selection.

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