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

The description adds the behavioral constraint of returning only direct, non-stop routes, which goes beyond the readOnlyHint annotation. The annotation already establishes that the operation is read-only and safe; the description enriches this by clarifying the filtering behavior. It does not mention edge cases like empty results, but given the readOnlyHint and the presence of an output schema, this is adequate.

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?

The description is a single, well-structured sentence that front-loads the main action and key constraint. It is concise without sacrificing necessary information, making it easy to parse quickly. No unnecessary words or repetition.

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?

Given the tool's simplicity (one parameter, read-only operation), full schema coverage, and existing safety annotations, the description provides all necessary context. It explains what the tool does, the direct-route filter, and the origin port requirement. The return value structure is presumably covered by the output schema, so there are no obvious gaps.

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 already has 100% coverage for the portLocation parameter, describing it as a 'Location name or search term used to find matching ports'. The tool description adds that this is the origin port ('from a given origin port'), clarifying the parameter's role beyond the generic schema description. This is meaningful additional context, though not extensive.

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 clearly states the tool's function: finding direct ferry routes without layovers. It uses a specific verb 'Find', specifies the resource 'direct ferry routes and reachable destination ports', and includes the key differentiator 'without layovers or transfers' which distinguishes it from trip search tools like search_trips that may include connections. An agent can immediately understand its purpose and difference from 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?

The description implies usage when direct connections from a single origin are needed, as it explicitly states 'without layovers or transfers'. However, it does not name alternative tools like search_trips or provide explicit when-not-to-use conditions. The usage context is only implied, not clearly delineated with alternatives or exclusions.

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