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

Annotations already cover the safety profile (readOnly, idempotent, closed-world), so the bar is lower, and the description adds genuine value beyond them: the dataset scope ('every airport worldwide that holds a three-letter IATA code and scheduled service'), the explicit exclusion of time zones, what the response contains (matched code type, distance in km), and a per-call price paid over x402 — details nowhere in the structured fields.

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?

Three sentences, front-loaded with the core lookup purpose, followed by scope, return semantics, an exclusion, and pricing. Dense but well-ordered; nearly every clause carries information, though the long first sentence could be split.

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 compensates by describing return contents (name, city, country, region code, coordinates, elevation, distance) and the matched code type, and it flags the time-zone omission and pricing. For a 5-param read-only reference tool this is close to complete, missing only pagination/tie-breaking behavior on proximity results.

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 schema already documents all five parameters including formats, ranges, and the near-dependency. The description adds only loose prose implying code-vs-near selection and does not contribute syntax or edge-case meaning beyond the schema, 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 and resource — look up an airport by IATA/ICAO code — and clearly enumerates the two modes (code lookup vs. proximity search) plus the fields returned. It is unambiguous about what the tool does, but it never names a sibling (e.g., geo_distance or ref_country) to differentiate itself 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 description presents the two usage patterns (lookup by code, or search by coordinate and radius), which implies when each mode applies, but gives no explicit guidance on when to choose this tool over alternatives, nor any exclusions beyond the schema's 'Only with near' constraints.

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