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

Annotations already state readOnlyHint, idempotentHint, and destructiveHint, but the description adds valuable behavioral context: it is a PAID endpoint ($0.02/call via x402) and returns a 402 without payment. It also discloses the return format. No contradiction with annotations.

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 well-structured and front-loaded: it states the primary action first, then usage context, alternatives, payment requirements, and return schema. Every sentence adds unique value, and it is concise without being overly terse.

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?

There is no output schema, so the description appropriately explains the return array structure. It also covers input requirements (port), optional parameters (days_ahead, x_payment), payment behavior, and tool alternatives. For a straightforward read-only tool with good annotations, this is complete.

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 100%, so the baseline is 3 per the rubric. The description does not add parameter-specific detail beyond what the schema already provides (port examples, days_ahead default). It references the port and days_ahead context implicitly but does not explain parameter formats beyond schema descriptions.

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: 'Get upcoming vessel arrivals and departures at a specific port.' It clearly distinguishes from siblings by explicitly naming shippingrates_transit and shippingrates_transit_schedules as alternatives for other use cases. It also lists the exact data returned, making the tool's purpose unmistakable.

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 a clear when-to-use context ('check what vessels are expected at a port — useful for booking planning and tracking') and explicitly names alternative tools for transit time estimates and service-level routing. This provides strong guidance on tool selection.

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