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

Annotations already declare readOnlyHint=true, destructiveHint=false, so the safety profile is covered. The description adds real behavioral context beyond the structured fields: a departure date is mandatory for every flown leg, and long multi-continent itineraries can return unpriceable because the tool prices a single fare rather than split tickets. It stops short of noting latency or how partial failures are surfaced, which keeps it at a 4.

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, front-loaded with the capability, then the routing rule, then the failure mode. Every sentence carries distinct information and none restates the title or annotations.

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 7-parameter read tool with an output schema absent, the description covers purpose, selection, prerequisites, and known failure modes, which is nearly everything an agent needs. It does not sketch the shape of a fare result (e.g. that multiple options come back), though maxOptions partially implies it.

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 cabin enums, '000' overland markers, and pax limits are already documented in the schema. The description only reinforces the flown-leg date requirement and adds nothing about syntax or formats beyond that, so baseline 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?

States a specific verb and resource ('Get live, bookable-quality fares for one specific itinerary') and pins the scope to actual flights and actual prices for given dates. It also implicitly separates itself from the ballpark sibling route_estimate, so an agent can route correctly without reading either schema.

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?

Gives an explicit trigger ('once the customer has settled on cities and dates and wants real numbers') and an explicit alternative with its own condition ('use route_estimate instead when dates are still open'). Nothing about tool selection is left to inference.

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