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

Annotations already declare readOnly, openWorld, idempotent, and non-destructive, so the safety profile is covered. The description adds meaningful behavioral context beyond that: it specifies 'Direct trains only (no transfers)' and that results include live delays and cancellations. It does not disclose rate limits or output structure, but with annotations present this is a strong addition.

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 compact and front-loaded: purpose and returned data come first, followed by a crucial scope constraint, then usage context and a minimal example. Every sentence earns its place with no 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?

For a read-only tool with no output schema, the description adequately covers what is returned (times, tracks, delays, cancellations) and when to use it. It omits details about the output list structure and does not reference sibling tools, but it is complete enough to call 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 67%: the schema already documents the from, to, date, and time parameters well, while results and time_is lack descriptions. The description's example shows expected values for from/to but adds no semantic detail for the undocumented parameters, so it does little beyond the schema.

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 resource (direct trains between two Finnish stations) and enumerates the returned data (departure/arrival times, tracks, live delays, cancellations). It also names the train operators covered. However, it does not explicitly distinguish this tool from its siblings (fi_find_station, fi_station_departures), so it falls short of a 5.

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 'Use when' line gives a clear context (someone travels by train in Finland, e.g. Helsinki to Tampere) and the example reinforces it. But there are no when-not conditions or named alternatives, so the agent receives no explicit routing guidance versus sibling tools.

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