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

Annotations already declare this a read-only, idempotent, open-world, non-destructive call, so the safety profile is covered. The description adds meaningful behavioral context beyond that: the data is live-only, there are no transfers, and the window is capped at 90 minutes, plus it previews the payload (departure/arrival times, live delay, current train position). No rate limits or failure modes are mentioned.

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 lines, front-loaded with the capability and scope, followed by a use case and a concrete call example. Nothing is padded, though the operator list in parentheses is slightly more than the agent strictly needs.

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?

There is no output schema, and the description correctly fills that gap by enumerating the returned fields (times, live delay, current position). Combined with the live-only and no-transfer constraints, an agent has enough to call and interpret the tool, with only the results-count behavior left implicit.

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 67%, and the "from" parameter is already richly documented in the schema (station names, codes, and the "Dublin" catch-all). The description's worked example {"from":"Dublin Heuston","to":"Cork"} usefully demonstrates accepted station formats, but "to" and the "results" limit remain thin, so the description only partially compensates.

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 gives a specific verb+resource+scope: direct Irish Rail trains between two named stations within the next 90 minutes, with the operator types listed (Intercity, Commuter, DART, Enterprise). An agent can tell this is a point-to-point live journey lookup, but the description never names its siblings (ie_station_departures, ie_find_station) to sharpen the boundary.

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 states an explicit use condition ("Use when: someone wants to take a train in Ireland now or soon") and a hard exclusion ("Live data only: no later days, no transfers"), which is real routing guidance. It stops short of naming an alternative tool for the excluded cases, so the agent must infer that ie_station_departures handles other departure queries.

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