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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds genuine behavioral value by disclosing the payload contents — live delay and cancellation data — which is important since no output schema exists. It omits the result-count cap (default 8, max 20) and any freshness/rate-limit 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 tight lines: capability plus returned fields first, then the usage condition, then a copy-pasteable example. No filler sentences and the most decision-relevant information is 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?

With no output schema, the field enumeration (time, train, destination, track, delay, cancellations) usefully compensates. The main gap is the undocumented 'results' limit and no guidance on resolving station names, but for a two-parameter read tool this is close to complete.

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 50%: 'station' is documented in the schema and the example ({"station":"Helsinki"}) reinforces the expected format. The 'results' parameter has no schema description and the description does not explain it, so half the parameters remain unilluminated beyond their names.

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?

States a specific verb and resource ('next train departures from one Finnish station') and enumerates the returned fields (time, train, destination, track, live delay, cancellations). It does not explicitly name or contrast with the siblings fi_find_station or fi_train_connections, but the single-station departures-board framing makes it functionally distinguishable.

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: someone is at (or going to) a station in Finland' line gives a concrete situational cue for invoking the tool. It stops short of stating when NOT to use it or routing to alternatives (e.g. fi_find_station for name resolution, fi_train_connections for A-to-B journeys).

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