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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the agent knows this is a safe, open-world read. The description adds useful context about real-time status and live times, but does not disclose rate limits, freshness guarantees, pagination, or permission requirements beyond what the annotations cover.

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?

The description is a single, front-loaded sentence with no filler. It efficiently states the resource, identifier, and returned content.

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 an output schema present, the description need not explain return values, and the annotations cover the read-only and open-world nature. The schema fully covers parameters. The only small gap is lack of routing guidance versus sibling tools.

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 the schema already fully documents place_id, lang, and country. The description only reinforces that place_id is required and does not add syntax, format, or constraints beyond what the schema provides.

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 names a specific resource (transit stop/station), the key input (place id), and the returned content (systems, lines, upcoming departures with live/scheduled times). This clearly distinguishes it from siblings like apple_maps_place, apple_maps_eta, and apple_maps_place_photos.

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 phrase 'by place id' implies the tool requires a place ID and is used for transit departure lookups, but it does not explicitly state when to choose this over apple_maps_place, apple_maps_search, or apple_maps_eta. No exclusions or alternative recommendations are provided.

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