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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint, so the safety profile is covered. The description adds useful context about transport modes and return fields (live delay, platform), but does not mention rate limits, authentication needs, or pagination behavior. With annotations carrying the safety burden, a 3 is appropriate.

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 tightly written sentences plus a compact example. The return fields are front-loaded, the usage condition follows, and the example is immediately actionable. No waste.

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 simple read-only, two-parameter tool with no output schema and annotations covering safety, the description gives sufficient purpose, usage condition, and returned data fields. However, the 'results' parameter behavior (default 8, max 20) is unaddressed, leaving a small gap for an agent that might need to control result count.

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 50%: the required 'station' parameter is documented in the schema, but the optional 'results' parameter has no description anywhere. The description's example only shows the station format and never addresses the results parameter, so it fails to compensate for the coverage gap.

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 ('Next departures from one Swiss station or stop') and details returned fields (time, line, destination, platform, live delay). It implicitly distinguishes from ch_connections (connections between stations) by focusing on departures from a single station, but does not explicitly name or contrast siblings.

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?

Provides a clear when-to-use condition: 'someone is at (or going to) a Swiss station and wants the next departures.' No when-not conditions or alternatives (e.g., ch_connections for multi-leg trips) are mentioned, so it stops short of full routing guidance.

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