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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds that the data source is Wikipedia (implying potential incompleteness or non-authoritative data) and the specific use case. However, it does not disclose any additional behaviors like pagination, return format, or rate limits. Given the annotations carry the core behavioral safety, a 3 is appropriate.

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?

Two concise sentences with zero waste. The core action is front-loaded in the first sentence, and the usage guidance is in the second. Every word earns its place.

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 read-only lookup tool with fully documented parameters and no output schema, the description covers the essential decision points (what it does, when to use it). It does not describe the output format or error handling, but these are not critical given the tool's simplicity and the annotations. A high score is justified.

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% – all parameters (airport_code, airline, destination) have descriptions in the schema. The tool description does not add any extra meaning beyond what the schema already provides. 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?

The description states a specific verb ('look up'), a resource ('Wikipedia airport page'), and the data ('airline service'). It clearly differentiates from sibling tools by positioning it as a fallback for false negatives on small markets and as the source for full destination lists. This is a precise, non-tautological purpose.

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?

Explicitly states when to use the tool: 'Use when fare/award tools say a route doesn't exist... or when you need the full destination list.' This provides clear triggers and implies a complementary role to other search tools. The 'Free, no auth' note also informs cost/access considerations.

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