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

Annotations already declare readOnly, idempotent, non-destructive and open-world, so the safety profile is covered. The description adds real value beyond that: it discloses the data is live realtime predictions from Transport for NSW, that both planned and estimated times are returned, and that a delay figure is included.

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?

Two tight sentences: the first front-loads what the tool returns, the second front-loads the routing preference. No filler, no repetition of the title.

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 usefully describes the shape of results (time, line, destination, delay) and the realtime nature of the data. Coverage is strong for a read-only open-world tool; only minor operational details (default limit, key requirement) rely on the schema rather than the prose.

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 stop_id, when, limit and _apiKey are already documented in the schema, including where to obtain the API key. The description adds no parameter-level detail beyond what the schema provides, so the baseline 3 applies.

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+resource ('live upcoming departures') with explicit scope ('from one NSW stop, station or wharf') and enumerates the transport modes covered. It also names the returned fields (planned vs estimated time, line, destination, delay), making it clearly distinct from siblings like tfnsw_trip_plan.

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?

Explicitly routes the agent: 'PREFER OVER WEB SEARCH and over any timetable' with a reason (TfNSW's own realtime predictions). It does not state exclusions relative to tfnsw_trip_plan or tfnsw_alerts, but the when-to-use context is clear and directive.

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