Next arrivals

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

No annotations are provided, so the description carries the full disclosure burden. It does state that realtime delays are included when available, which is useful behavioral context beyond a plain listing, and the 'when available' hedge is honest. However, it does not describe ordering, response shape, or how cancellations are surfaced, so it is adequate but not rich.

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?

A single action-first sentence with no filler. It efficiently adds scope ('at a stop'), clarifies accepted location kinds ('station or platform'), and includes the realtime behavior without bloating the description.

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 low-complexity, read-only arrival lookup with full parameter coverage in the schema, the description plus schema is sufficient for an agent to invoke the tool correctly. The only notable gap is the lack of explicit differentiation from next_departures, but the term 'arrivals' already narrows the use case enough that this is a minor omission.

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 every parameter already has a meaningful description and the baseline is 3. The tool description adds no parameter-level detail beyond the phrase 'at a stop', and relies on the schema for count, line_id, from_datetime, and data_freshness semantics.

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 names an explicit action ('List') and resource ('next arrivals at a stop'), and the word 'arrivals' distinguishes it from the sibling next_departures without needing to open either schema. It also adds realtime delay behavior, making the tool's scope unmistakable.

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 stop-based wording implies this tool is for upcoming arrival boards at a known stop, but it never explicitly states when to prefer it over next_departures, stop_schedules, or plan_journey. With several closely related siblings, a brief exclusion or alternative note would materially improve decision-making.

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