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

Annotations already declare readOnlyHint=true, openWorldHint=true and destructiveHint=false, so the safety profile is covered. The description adds genuinely useful context beyond that: the tool is a paid call at 2 credits and returns miles, kilometers and estimated flight duration, which affects an agent's decision to spend the credits.

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?

It is short and front-loaded, but it opens by restating the title ("Airport Distance: Airport Distance") and then says the same thing twice — distance and duration are mentioned in both the first and second sentences. The credits note is useful and well-placed at the end.

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 simple two-input lookup with an output schema, an annotation-backed safety profile and an explicit credit cost, this is largely complete. The remaining gap is behavior on unknown or mismatched codes and how the ICAO parameters interact with the IATA ones.

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 both IATA and ICAO parameters are already documented, establishing the baseline of 3. The description adds no meaning beyond the schema and in fact narrows it by saying the calculation uses "3-letter IATA codes", leaving unclear whether the ICAO parameters are alternatives or whether only IATA is accepted.

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 verb and resource: it "calculates the great-circle distance between two airports" and returns distance plus flight duration. That is clearly distinct from generic siblings like DistanceCalculator or from AirportCodeConverter/AirportsLookup, 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?

Usage is only implied by the purpose statement: an agent can infer it is for airport-to-airport route distance. There is no explicit when-to-use guidance, no mention of alternatives such as DistanceCalculator for non-airport distances or AirportCodeConverter for resolving codes.

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