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

Beyond the readOnlyHint annotation, the description discloses non-obvious behavioral traits: results are capped at 25, fuel is extremely rare in the dataset, and the response includes an `amenity_availability` field where a missing record does not mean the amenity is absent. This is exactly the kind of contextual behavior an agent needs to interpret results correctly.

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 longer than minimal, but every sentence earns its place: purpose, filters, limit, language handling, and the important fuel/data caveats. It is well-structured and front-loaded, though a slight trim could tighten it further.

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 tool with no output schema, the description covers the key invocation facts: return limit, amenity filtering behavior, and a non-obvious response field. It does not enumerate other return fields, but that is not necessary for correctly selecting and calling the tool.

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?

Input schema covers 75% of parameters, but the description adds meaningful value: it explains that country names work in Dutch or English, that province spelling variants are matched together, and that fuel combined with other amenities usually yields zero results. These details go beyond the schema's enum and descriptions, though the schema already covers the basic semantics.

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 opens with a specific verb and resource: "Find European marinas (jachthavens) that match a set of amenities: electricity, water, fuel, wifi." It clearly distinguishes the tool from boat/rental siblings by naming marinas and their specific amenity criteria, leaving no ambiguity about what it searches.

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 provides clear functional context and even includes a practical caveat that fuel is rarely recorded, but it does not explicitly state when to prefer this tool over alternatives or mention any exclusion scenarios. Usage guidance is implied rather than explicit, so it falls short of a 4.

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