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

Annotations already cover the safety profile (read-only, open-world, idempotent, non-destructive), and the description adds genuinely useful operational context the annotations cannot: free-tier answers lag 24 hours, are capped to a 1 square degree box, and consume 1,000 credits a month while paid plans are live. It still says nothing about result ordering logic, default radius for proximity searches, or what fields come back, so the disclosure is valuable but partial.

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?

Two dense sentences, front-loaded with the capability statement followed by quota/access terms; nothing is wasted. The phrasing 'Free. Free accounts too:' is slightly clumsy and forces a re-read, but it keeps the commercial constraints compact.

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?

With no output schema, the description carries the burden of explaining results, and it does so minimally ('ranked for a seafarer') while fully explaining access tiers and limits. For a small, read-only lookup tool with four well-documented optional parameters, this is close to sufficient; only return-field and proximity-radius details are absent.

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 all four parameters are documented in structured form; the description's only added meaning is that query and the near_lat/near_lon pair are alternatives rather than combinable, and that the output is relevance-ranked. The 1 square degree box implicitly constrains the proximity parameters but no default radius or unit behavior is stated.

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?

States a specific resource (ports) with two clearly separated retrieval modes: lookup by name/UN/LOCODE/English name, or proximity to a position. The phrase 'ranked for a seafarer' signals it is a relevance-ordered search rather than a live-status tool, which separates it from siblings like port_now or port_congestion, though no sibling is named explicitly.

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 'or the ports nearest a position' clause, mirrored by the 'Or:' prefixes in the schema, tells the agent which parameter family to pick for which intent. It also sets expectations about free-account freshness and area caps. What's missing is any explicit 'do not use this for X' or a pointer to a different tool when live data is required.

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