apple_maps_transit_departures

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

With no annotations, the description carries the full disclosure burden. It is transparent about the return contents (systems, line metadata, departure times) and the error condition ('A place that is not a transit stop returns 404'). It does not mention rate limits, authentication, or the coverage horizon of 'upcoming departures,' which would add further transparency, but nothing it does say is contradicted or misleading.

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?

All four sentences earn their place: purpose, return content, input identification, and error condition. There is no redundant explanation of lang/country because the schema already covers them. The description is front-loaded with the main purpose and keeps the material tight.

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?

Given the tool has only 3 parameters, no output schema, and no annotations, the description is complete. It explains what is returned (systems, lines, departure details), how to get the required place_id, the optional language and country are in the schema, and it specifies a critical error case (404 for non-transit stops). An agent has everything needed to select and invoke this tool 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% for all three parameters, so the baseline is 3. The description adds contextual guidance for place_id (how to find the ID via search) and mentions a station name example, which is mildly useful, but it does not meaningfully extend the parameter meanings 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?

The description opens with a specific verb+resource: 'Get a transit stop's lines and live departures from Apple Maps.' It then enumerates return fields (systems, lines with name/shield/color, departures with scheduled/live times and status). This clearly distinguishes it from sibling Apple Maps tools like directions, eta, place, or search.

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 description gives clear context for when to use this tool: when you need a transit stop's systems, lines, and upcoming departures. It states the required input and even tells how to obtain the place ID ('find stops with the search endpoint'). It does not name specific exclusionary alternatives, but the purpose is distinct enough that an agent can infer when this is the right tool.

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