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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds genuinely new behavioral detail beyond the annotations: results are sorted nearest-first and distances are expressed in km, which tells the agent what the response looks like.

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?

A single tight sentence with zero filler. The core action and its geographic scope are front-loaded, and the sorting/units detail is appended efficiently.

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 read-only search tool with no output schema, the description usefully discloses the return ordering and distance unit. Safety is covered by annotations and limits by the schema. Only the lack of alternative routing keeps it from being fully 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 coverage is 100%, with defaults and max values documented for limit and radius_km in the schema itself. The description restates lat/lon/radius implicitly but adds no syntax, format, or constraint detail beyond what the schema already provides, so the baseline of 3 applies.

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 verb (Find), a named data source (NGA World Port Index ports), and precise scope (within a radius of a lat/lon point, sorted nearest first, distance in km). An agent can distinguish it from the geographic siblings port_lookup and ports_by_country purely from this sentence.

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 radius-around-a-coordinate framing implies the spatial use case, so the intended scenario is inferable. However, it never explicitly contrasts with port_lookup or ports_by_country, nor states when this spatial search is preferred over those alternatives, leaving routing guidance implied rather than stated.

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