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

Annotations already declare readOnlyHint=true and destructiveHint=false, and description adds a unique behavioral trait: the tool is PAID with $0.02/call via x402 and returns 402 when unpaid. This explains a critical non-standard behavior not available from annotations. It also clarifies the return fields structure. Minor gap: doesn't mention pagination or rate limits, but annotations cover safety.

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?

Description is well-organized: a one-sentence purpose, a context paragraph, explicit sibling differentiation, payment note, and return format. It uses bullet-like structure via line breaks, is front-loaded with the main purpose, and every sentence adds distinctive info. Efficient and uncluttered.

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 no output schema, the description explicitly provides the return array structure (vessel_name, carrier, voyage, eta, etd, service, from_port, to_port). It covers payment requirements, default behavior, and alternate tools. For a list-type tool with 3 params and full schema coverage, this is complete enough for agent use.

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%, so the baseline is 3. The description adds value by explaining the purpose of the main 'port' parameter (examples given in schema) and by noting the default for days_ahead (14) which is not in the schema, and clarifying the x_payment header. It doesn't add syntax details but compensates with context beyond schema.

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 it gets upcoming vessel arrivals/departures at a specific port, with a specific verb ('Get') and resource ('vessel arrivals and departures'). It lists specific return fields and distinguishes itself from sibling tools like shippingrates_transit and shippingrates_transit_schedules by naming alternatives.

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?

Provides explicit use cases ('useful for booking planning and tracking') and explicit alternatives for different needs ('For transit time estimates... use shippingrates_transit. For detailed service-level routing, use shippingrates_transit_schedules.'). This clearly guides when to use this tool vs alternatives.

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