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

Annotations already declare the safety profile (readOnly=false, destructive=false, idempotent=false), so the bar is lower. The description adds real behavioral context: the operation is additive, multiple options are expected, and it clarifies the roundTrip cost semantics. It stops short of describing return values or auth, but this is solid added value over the structured hints.

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 tight sentences, front-loaded with the purpose, then usage, then the sibling redirect. No filler; every sentence carries information the agent needs.

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 nested-object, no-output-schema tool, the description covers what the tool does, when to use it, and the key semantic field. Given the schema carries all required-parameter documentation, nothing critical is missing, though it does not hint at how the option is keyed or identified afterward.

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 a 3 would be the baseline. The description goes beyond it by explaining the meaning of roundTrip ('when the price covers the return leg too'), a non-obvious semantic not stated in the schema. It does not address the related roundTripReturn / outboundIncludesReturnCost fields, keeping it from a 5.

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 a concrete verb and resource ('Propose a way of travelling TO a destination') and enumerates the transport modes covered. It explicitly contrasts with the sibling add_getting_around_option, so an agent can distinguish the two without opening 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?

It states the when ('one option per candidate itinerary; add several so the user can compare price against travel time') and the when-not with the named alternative ('For moving around once there, use add_getting_around_option instead'). The routing decision is fully specified.

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