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

Annotations already mark the tool as read-only, idempotent, and non-destructive. The description adds meaningful runtime behavior: results are ranked by Starlink probability, an empty result means the route is not served by Starlink planes, and there is no connection logic or coverage-ratio ranking. There is no contradiction with the annotations.

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 pack the trigger, behavior, parameter pattern, alternative, and empty-result semantics with no filler. The most important usage information is front-loaded.

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 three-parameter lookup with no output schema, the description covers when to use it, how to combine parameters, what results contain, what an empty result means, and when to choose an alternative. The schema handles the default limit, so nothing needed to call the tool correctly is missing.

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?

The schema fully documents all three parameters with types, examples, and a default for limit. The description adds the key combination rule—pass both origin and destination for a route, or one for an airport list—which is not evident from the schema alone.

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 opens with explicit user-query triggers and a precise statement of behavior: returns United Airlines flight numbers on a route or touching an airport, ranked by Starlink probability. It names the closest sibling (plan_starlink_itinerary) and contrasts this tool's single-route scope, so the agent can distinguish it from the itinerary planner.

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 gives concrete when-to-use examples ('Use when the user asks...'), specifies the two valid calling patterns (both origin+destination or just one), and explicitly routes connection-based trip planning to plan_starlink_itinerary, stating 'this tool has no connection logic or coverage-ratio ranking.'

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