train_service

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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint, so the safety profile is covered. The description's extra content (live status, expected/actual times, platform) is largely return-value detail that the output schema already carries, leaving only the mild conditionality of 'a train running today' as genuinely new behavioral context.

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?

Three short sentences, front-loaded with the payload description and closing with the actionable parameter hint. No filler.

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 covering the return shape and annotations covering safety, the definition is nearly self-sufficient for a one-parameter read tool. A brief note on behavior for trains not running today would close the remaining gap.

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 0%, so the schema alone leaves `trip_id` undefined. The description compensates by stating where the value comes from (rail_departures), which is exactly the missing semantic an agent needs, though it doesn't describe format or validity constraints.

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 states a specific resource and scope: 'Every station one train calls at,' which tells an agent this enumerates the calling pattern of a single rail trip. It implicitly distinguishes itself from rail_departures (the originator of trip_id) and from bus_service, though it never draws that contrast explicitly.

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?

It gives clear context: the required `trip_id` is obtained from rail_departures, effectively positioning this as a follow-up call. It stops short of explicit when-not-to-use guidance but the workflow is unambiguous.

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