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

Beyond the readOnly/openWorld/idempotent annotations, the description discloses important behavior: for mode=bus it always queries the official live endpoint /api/public/v1/bus/live-arrivals, and if the live source fails, the only fallback is an estimated_eta from the predictive engine, clearly flagged as ESTIMATED. This tells the agent about data provenance, freshness, and reliability.

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 a compact set of three sentences with no filler. It front-loads the purpose and service scope, then provides prerequisites, and finally the important live-data/fallback behavior. Every sentence earns its place.

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?

The description covers modes, prerequisites, live-source behavior, and fallback semantics, while the schema documents all six parameters with 100% coverage. The main gap is the absence of an output schema and no mention of return format or how stop IDs are discovered, but this is minor for a schedule-lookup tool.

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 coverage is 100%, so the baseline is 3. The description adds value by linking modes to the entity the agent must supply — parada for bus, estación for TRAM, destination for coach — and by naming the C6 line for airport_bus. It does not need to restate schema details.

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 states exactly what the tool returns — próximas llegadas o salidas — and enumerates the concrete service types and lookup keys (bus por parada, TRAM por estación, Cercanías/ADIF, autobús interurbano por destino, C6 del aeropuerto). This clearly distinguishes it from siblings like find_transit_stop, which focuses on stop discovery rather than schedules.

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 gives clear context on how to use the tool: identify the service and the stop/destination, and it maps each mode to the required lookup concept. It does not explicitly name alternatives or state when not to use this tool, so it stops short of a 5.

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