next_arrivals

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

With no annotations, the description bears full responsibility for behavioral disclosure. It indicates that arrivals are upcoming, sorted, and that the 'minutes_from_now' field is pre-computed. It does not mention destructive behavior (none expected), rate limits, or data freshness, but the core behavior is clearly conveyed. Some minor gaps exist (e.g., whether past arrivals are excluded), but overall transparency is good.

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?

The description is extremely concise with only two sentences. The first sentence delivers the core purpose, sorting, and scope. The second sentence adds a helpful analogy and a key output detail. No information is redundant or extraneous, and the most critical facts are front-loaded.

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?

Given that the tool has 3 parameters and no output schema, the description adequately explains the output returns a sorted list with the 'minutes_from_now' field. However, it does not describe the full output structure (e.g., route names, arrival times), which an agent might need for correct handling. The description is sufficient for basic usage but could be more complete about the return format.

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?

The input schema has 100% description coverage, so the baseline is 3. The description adds value by highlighting the pre-computed 'minutes_from_now' field in the output, but it does not elaborate on parameter usage beyond what the schema already states (e.g., 'stop_id' is a GTFS ID, 'route_id' filters). Thus, the description provides minimal additional semantic context for the parameters.

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 clearly states the verb 'Get', the resource 'upcoming arrivals', and the context 'at a specific stop, across all routes, sorted by predicted arrival time'. It uses a vivid analogy 'Equivalent to a digital departure board', making the purpose immediately understandable. This tool is distinct from siblings like 'trip_updates' or 'alerts', which do not focus on per-stop arrival lists.

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 description implies usage for quick stop-level arrival lookups via the 'digital departure board' analogy, but it does not explicitly state when to use this tool over alternatives (e.g., 'trip_updates' for trip-level data). There is no mention of prerequisites or situations where the tool should not be used, which leaves the agent without important decision criteria.

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