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

Annotations cover the safety profile (readOnly, idempotent, non-destructive, open-world), yet the description adds substantial behavior beyond them: up-to-a-mile walking radius, transfer count and 0.3 km transfer-distance limits, 10-minute wait preference, and the crucial freshness distinction that live updates apply only to 'leaving now' while future departures are pure timetable. It also flags special airport behavior at BWI/DCA/IAD and imposes an answer-only-from-results constraint.

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?

It is front-loaded with the core behavior and largely dense, but the intermediate paragraphs stack many routing-policy clauses that could be tightened, and the closing 'answer only from results / unofficial tool' boilerplate is a directive rather than tool semantics.

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 still tells the agent what an option contains (walking time, transfer waits, live-update status, airport step), so the agent knows what it will receive and how to present it. Nothing needed to call it correctly 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 0%, so the description must carry the burden and it does: origin/destination accept an address, landmark, station, or 'lat,lon' with a pointer to geocode_address output as the preferred form, and depart_at is specified as local Eastern time in 'YYYY-MM-DDTHH:MM' format with an explicit omit-to-leave-now default.

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 a specific verb and resource — returning real trip options from agency timetables between an origin and destination — and explicitly contrasts itself with plan_connection, so an agent can route between them 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?

It gives an explicit trigger ('whenever a rider asks how to get somewhere at a particular time') and names the alternative with its own trigger ('use plan_connection for general "how would I get there" and which days it works'). No inference is required.

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