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

Annotations already establish read-only, idempotent, open-world, non-destructive behavior, so the bar is lower. The description adds useful behavioral context beyond annotations: coverage of all Swiss operators and inclusion of live delay data. It omits pagination/return-shape and rate-limit details, but the added operational context is genuine.

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?

Front-loaded with the core purpose and scoped with a single 'Use when' clause plus one compact example; no wasted sentences. The example is borderline redundant with the schema's station examples, keeping it just short of a 5.

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 description usefully enumerates what comes back (departure/arrival times, platforms, transfers, live delays), which tells the agent what to expect. For a 6-parameter open-world query tool this is nearly sufficient, though timing-parameter usage remains unexplained.

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% (mid-range), so the schema already documents most parameters including defaults for date, time, results and time_is. The description adds only an example object illustrating from/to, not semantics for the optional timing parameters, so it neither compensates for gaps nor falls below baseline.

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+resource (journeys between two places) with the transport modes and operator coverage (SBB/CFF/FFS, PostBus, all Swiss operators), and lists the returned content: times, platforms, transfers, live delays. This clearly separates it from siblings ch_find_station and ch_station_departures.

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 concrete trigger plus an example (Zürich to Geneva), which is clear context for selection. It stops short of naming alternatives or exclusions, e.g. when to prefer ch_station_departures over this tool, so it doesn't reach the top of the scale.

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