get_arrivals

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

No annotations are provided, so the description carries the full burden. It usefully discloses the cross-tool dependency and a hard input constraint, but says nothing about whether data is live vs scheduled, pagination, rate limits, or error behavior for an unknown/closed station.

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 sentences with zero waste. The purpose is front-loaded and the critical constraint is escalated with a NOTE rather than buried.

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 2-parameter read tool, the description covers the main failure mode (passing a station name). With no output schema and no annotations, it could say a bit more about what an arrival record contains, but nothing essential to correct invocation is missing.

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 100%, so both parameters are already documented, including the 'get this from get_station_info first' note on stationId. The description only reinforces the stationId rule and adds nothing about the optional line filter; baseline 3 is correct when the schema does the heavy lifting.

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 with scope: 'Get next train arrivals at a station.' The word 'train' implicitly separates it from the sibling get_bus_arrivals, so an agent can route without opening either schema.

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 NOTE gives an explicit prerequisite ('First call get_station_info to get the stationId') and an anti-pattern ('Do not pass the station name directly'), which is genuinely actionable. It does not name alternative arrivals tools or say when not to fetch arrivals at all, so it stops short of a full when/when-not/alternatives treatment.

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