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

Annotations already declare readOnly, idempotent, closed-world and non-destructive, so the bar is lower; the description still adds real context: a hard 20-result cap, deterministic ordering ('larger harbors first'), no API key requirement, and the caveat that harbor size only exists for World Port Index ports. It does not say what an empty result looks like, but the operational profile is well covered.

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 accepted query modes are front-loaded in the first clause, followed by the return fields, then two short constraint sentences. It is dense but every clause carries information; the only mild cost is a long comma-laden first sentence that takes effort to parse.

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 describing returns and does so by enumerating every field, plus the port-area radius used for port-call detection. Combined with the result cap and ordering, an agent has everything needed to call this reference-lookup tool correctly.

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 earns above that by clarifying that 'query' matches on part of a name, giving format examples for locode and country, and reinforcing the 20-item ceiling that pairs with the limit parameter. It stops short of explaining precedence when multiple filters are supplied together.

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') and resource ('ports') and enumerates the three accepted lookup modes with concrete examples (FIHEL, FI). It also lists exactly what comes back (id, name, country, UN/LOCODE, position, harbor size, port-area radius), so an agent can distinguish it from vessel-oriented siblings like get_vessel or port_calls at a glance.

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 implicitly defines when the tool is appropriate by spelling out the three valid query forms, and the note that id is 'for port_calls' hints at the downstream sibling relationship. But there is no explicit 'use this instead of X' or exclusion guidance against port_calls or vessels_near, leaving the routing inference to the agent.

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