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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, and openWorldHint=false, so the safety profile is clear. The description adds meaningful behavioral context by disclosing the tool's scope, explicit exclusions (no live fares, no booking), and inclusion of typical car hire costs, which helps the agent understand what information will be returned.

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 description is a single front-loaded sentence that lists the covered domains and the important exclusions without any filler. Every clause contributes directly to scope understanding.

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 zero-parameter informational tool with an output schema and full annotations, the description covers the essential aspects an agent needs: what is covered, what is explicitly not covered, and related cost information. The output schema handles return details, though the description could be slightly stronger by explicitly stating that it returns a structured capabilities summary.

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?

There are zero parameters, so the baseline is 4. The description correctly adds no parameter guidance because none is needed, and it uses the space to explain the tool's informational content.

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 makes clear that this tool describes Airfare Brain's coverage: airlines, fee research, limitations, and destination car hire costs. It effectively distinguishes scope from siblings like airline_fees and trip_at_airport, though it relies on the title for the explicit 'get' verb rather than stating an action in the description itself.

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 lists what the tool does NOT do (no live fares, no booking) and defines coverage boundaries, implying it should be used as a reference before other tools. However, it does not explicitly say when to call it versus alternatives or that it should be called first, leaving usage to inference.

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