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

Annotations already declare readOnlyHint=true, idempotentHint=true, and openWorldHint=false, so the safety profile is covered. The description adds valuable context: that the data is purely scheduled (not real-time) and that stops are returned 'in order,' which are behavioral traits an agent needs beyond the 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?

Two sentences, no filler. The core purpose is front-loaded (first sentence states exactly what the tool returns), and the second sentence adds a critical constraint in one clause. Every word earns its place without redundancy.

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 tool is simple (one parameter, no output schema) and the description adequately explains the output content and its scheduling nature. It does not specify the exact format of return values (e.g., whether times are ISO strings), but for such a basic read-only tool this is not a severe omission, and annotations cover the read-only aspect.

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?

With 0% schema description coverage, the description must compensate for parameter documentation, but it does not mention the train_number parameter at all. The name is self-explanatory and the schema gives a pattern, so there is minimal ambiguity, but the description adds no semantic meaning beyond what the schema already 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 clearly states the tool returns 'every stop of one train with its scheduled arrival and departure, in order.' This specifies the verb (provide/return), resource (one train's stops), and scope (entire itinerary), distinguishing it from sibling tools like station_departures that cover multiple trains from a single station.

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 says 'Scheduled times only — this says nothing about where the train is today,' which implies this tool is not for real-time tracking, but it does not name specific alternatives or give explicit when-to-use guidance. The usage context is only implicitly derived from the contrast with real-time status, falling short of explicit routing.

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