next_trains

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

Annotations already cover read-only, idempotent, and open-world behavior, so the bar is lower. The description still adds real value beyond them: it names the upstream data source (SEPTA NextToArrive), discloses that connecting trips are synthesized when no direct train exists, and documents graceful degradation to the published schedule if the live API is down.

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?

Three short sentences with the primary capability front-loaded and the implementation/fallback details trailing. Nothing is redundant, though the API name (NextToArrive) is somewhat implementation-oriented relative to agent decision-making value.

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 should indicate what comes back; 'with live delay status' hints at delay fields but omits the return shape, ordering, or whether connecting legs are returned as separate segments. For a live-data tool where degraded mode changes result semantics, station-format and result-count guidance are the main missing pieces.

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 0%, so the description carries the full burden of parameter meaning. It conveys the from→to direction but says nothing about station identifier format (abbreviation vs. full name, which matters given the find_station sibling) or what 'count' controls, and the default of 5 appears only in the schema with no explanation of result-set behavior.

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 — next trains from one station to another right now, with live delay status. The temporal qualifier ('right now') implicitly separates it from train_schedule, but it never names a sibling explicitly, so an agent must still infer its boundary against station_departures (same station) and train_schedule (published times).

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?

Usage context is implied by 'right now' plus the schedule-fallback note, which signals this is the live/imminent-departures tool. There is no explicit statement of when to prefer station_departures, train_schedule, or train_status, and no prerequisite guidance (e.g., resolving station names via find_station first).

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