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

With readOnlyHint and openWorldHint already set, the description adds valuable behavioral context: the data source, AIS derivation, real-time lag, and the distinction between past calls and forward schedules. It also discloses pricing ($0.002 USDC per successful call via x402) and that failed calls are not charged.

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 front-loaded with the core identity of the dataset, then immediately clarifies the historical nature and lag, and ends with the pricing/payment terms. Every sentence adds useful selection or invocation context without waste.

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 output schema exists and both parameters are fully documented in the input schema, the description supplies the remaining context an agent needs: data source, historical-vs-forward distinction, recency limitation, and payment behavior. Nothing critical for correct selection or invocation is missing.

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 two parameters are already well documented as a PortWatch port name and a days value with range/default. The description adds only mild context such as 'at one port' and 'most recent days'; it also mentions 'by ship type,' which is not a selectable parameter and introduces slight ambiguity.

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 states a specific data resource (recorded daily port calls / vessel arrivals at one port), source (IMF PortWatch, AIS-derived), and time scope (most recent days). It clearly distinguishes this from a forward arrival/departure schedule, though it does not explicitly name sibling tools such as vessel_tracker or port_congestion_index.

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?

It gives clear usage context by stating these are past calls, not a forward schedule, and that the latest date lags real time. It does not explicitly route the agent to alternative tools for live tracking or congestion data, so it falls short of full when-to-use/when-not/alternatives guidance.

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