Transit Departures

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

Beyond the annotations (readOnly, openWorld, idempotent), the description adds context: 'minute-fresh departures including delay for ONE stop', data source ('GTFS-RT/HVV/VGN'), and the requirement for a stop ID. It does not contradict any annotations.

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 concise yet informative, with four sentences each serving a distinct purpose: stating the main function, citing the data source, differentiating from a sibling tool, and explaining the prerequisite. No unnecessary words.

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 presence of an output schema (not shown but indicated true) and the complexity of real-time departures, the description provides sufficient context: it clarifies the data source, the real-time nature, the restriction to one stop per call, and the need for prior stop discovery. It fully prepares the agent for correct usage.

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 coverage is 100%, so both parameters are already described in the input schema. The description adds value by explaining the relationship between `slug` and `stop_id`, noting that `stop_id` must be discovered via another tool, and providing format examples for `stop_id`. This augments the schema without redundancy.

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 clearly states the tool's purpose: 'Get live public-transport departures with real-time delays for a stop.' It specifies the verb, resource, and scope, and distinguishes itself from the sibling `get_city_resource` by noting it returns dynamic departures for a single stop.

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 explicitly tells when to use this tool (for live departures with delays) and contrasts it with the static stop list tool, providing an alternative. It also outlines a prerequisite: first fetch transit stops via `get_city_resource(slug, resource='transit')` to obtain valid stop IDs.

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