live_arrivals

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

With no annotations, the description carries the behavioral burden. It discloses a meaningful data-source precedence and that results are approximated to the next ~2 hours. This is beyond what the schema or annotations would show, though it leaves other live-data behaviors (update cadence, cancellation handling) unstated.

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?

Two sentences deliver the core purpose and the data-source fallback with no filler. The main limitation is jargon ('RTT'), but the structure itself is appropriately sized and front-loaded.

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?

The presence of an output schema excuses return-value detail, and the description covers purpose and behavior. However, it does not orient the agent relative to the sibling tools or explain the acronym, leaving moderate context gaps for a 4-parameter tool with no annotations.

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?

The description adds no parameter-level semantics; station, rows, from_station, and include_calling_points are left entirely to the schema. Schema description coverage is only 50%, so the description should compensate for the undocumented parameters but does not.

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 identifies the resource ('arrivals') and the time window ('next ~2 hours'), and the tool name reinforces a station-level live arrivals lookup. It stops short of a verb form and does not explicitly contrast with live_departures, so it loses a point.

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?

No when-to-use guidance is provided. The fallback chain ('Darwin's arrivals product if configured, then RTT, then booked timetable times') describes data sourcing, not when to choose this tool over live_departures, timetable, or service_details. None of the sibling tools are mentioned.

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