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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds real behavioral context beyond that: what the response contains (duration and distance per mode, handoff buttons for Uber/Lyft/Waymo/Maps), that ground time excludes airport check-in and security, and which data classes are unavailable.

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 core action and scope, then layers returns, the 'home' convenience, a caveat about ground time, and an availability disclaimer. Every sentence carries information, though the final two sentences are slightly list-like and could be tightened.

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?

With no output schema, the description must describe return values, and it does so at a summary level (duration/distance estimates plus booking handoff buttons). Combined with full schema coverage of the five parameters, an agent has what it needs, though return format details and pagination/limits remain unspecified.

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 all five parameters including the enum values and the 'home' origin sentinel are already documented in the schema. The description's restatement of the 'home' behavior and the supported modes duplicates rather than extends that, so the 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 (Compare) and resource (route summaries between two places) and enumerates the supported modes, which cleanly separates it from siblings like flight_route_lookup or places_search. An agent can identify this as the multi-modal ground routing tool without opening the 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 clear context for use (comparing driving/transit/walking/bicycling between two places) and effective exclusions by stating what is unavailable (fares, detailed legs, flights, ferries), which routes the agent elsewhere for those needs. It does not, however, name a specific sibling alternative or state prerequisites, so it stops short of full when/when-not guidance.

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