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

Annotations already cover the safety profile (readOnly, non-destructive, closed-world), so the bar is lower, yet the description adds real substance: it discloses the internal evaluation set, direction detection, backtracking analysis, alliance feasibility, surface sectors, and carrier selection. It does not describe the response shape or any cost/latency behavior.

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?

Front-loaded with the entry-point role, then capabilities. Four sentences are mostly load-bearing, though the closing 'The customer doesn't need to know...' sentence is more marketing than instruction and could be trimmed.

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?

There is no output schema, so the description must carry more of the return-value burden; it says it 'recommends the best approach' but never sketches what a recommendation contains. Still, for a read-only planning tool with fully documented params and clear annotations, an agent has enough to invoke it correctly.

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% and all four parameters are documented in-schema, so the baseline of 3 applies. The description only gestures at the 'cities' input ('Give it your cities') and adds nothing about pax, budget, or preferences beyond what the schema already states.

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 ('plan') and resource ('multi-city route') and positions itself as the umbrella entry point that internally evaluates Star Alliance RTW, oneworld RTW, and custom mixed-carrier builds. This implicitly distinguishes it from narrower siblings like custom_route_build, route_suggest, and route_validate.

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 primary entry point for any multi-city trip' gives a clear condition for reaching for this tool, and the closing line clarifies it should be preferred when the trip type is unknown. No explicit when-not guidance or named alternative is given, so it falls short of a 5.

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