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

Annotations already declare readOnlyHint=true, and the description does not contradict that. It adds useful behavioral context: this is an itinerary-construction tool that recommends carriers and handles non-alliance fare structures, rather than a simple fare lookup. It stops short of describing response format or side-effect details, but with readOnly annotations the gap is small.

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?

Four short sentences; front-loaded with the core action, then capability examples, then an explicit usage rule. The '90% of itineraries' sentence is mildly promotional but reinforces the tool's role as the default for complex routes.

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 moderately complex tool with no output schema, the description explains when to use it, what it produces, and what route shapes it handles. It doesn't detail return structure or error behavior, but the input schema and annotations cover the remaining invocation needs.

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 covers 100% of parameters with clear descriptions and enums, so the description isn't required to restate parameter details. The description adds contextual color (LCCs, surface sectors, Gulf bridge) that helps interpret budget/preferences, but this doesn't significantly extend the schema's already-strong parameter documentation.

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 uses a specific verb ('Break') and resource ('complex multi-city itinerary') and clearly states the deliverable ('individually-ticketable segments with carrier recommendations'). It also distinguishes itself from sibling route/fare tools by targeting routes that don't fit alliance fare rules.

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?

Explicit positive trigger: 'Use this for any route with 4+ stops, backtracking, or region combinations that alliance fares can't cover.' It also gives domain context (mixed carriers, LCCs, Gulf bridge, surface sectors), but it doesn't name when-not-to-use or point to alternative sibling tools, so not a 5.

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