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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint false. The description adds value by disclosing input flexibility (harbor name, region name, slug, identifier) and the rule that at least one side is required. This complements the structured annotations without contradiction.

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 two sentences, front-loaded with the core purpose and immediate return-value expectations. Every sentence adds operational detail; there is no fluff or repetition of schema information.

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 complexity (9 parameters, optional inputs, output schema), the description provides sufficient context: what is searched, what is returned, allowed input formats, and an edge-case constraint. The output schema covers return formatting, so this description is complete enough for an agent to invoke correctly.

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 56%, so the description partially compensates. It clarifies that origin and destination accept multiple formats and that at least one must be provided, which is not evident from the schema alone. It also explains that nationality affects fare band. However, it does not elaborate on adult/child/infant/limit parameters beyond their schema types.

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 uses a specific verb ('Searches') and clearly identifies the resource ('scheduled ferry and fast-boat departures between two places on a given date'). It lists concrete return fields (times, operator, vessel, duration, seats, fares), which distinguishes it from sibling tools like charter_search and fishing_search that target different types of transport.

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 gives clear context for when to use this tool (scheduled sea transport) and states an important constraint ('at least one side must be given'). It also references locations_list as a source for identifiers, implying a workflow. However, it does not explicitly mention when not to use it or directly contrast it with alternatives.

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