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

Annotations provide no safety hints, so the description carries the burden. It does disclose a notable behavior: outside London it shows the published timetable and 'says so' in the output. However, it does not explicitly state that this is a read-only operation or describe potential response format or limitations.

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 two sentences, front-loaded with the core purpose. The second sentence adds important contextual detail about data freshness and geographic variation, with no unnecessary content.

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?

For a simple single-parameter tool with no output schema, the description covers the essential context: what it returns, input format, and source behavior. It could be slightly more explicit about output details (e.g., time range or format), but the low complexity makes this sufficient.

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%, with the 'stop' parameter already described as 'Stop name or id, e.g. ...'. The description adds no additional meaning beyond the schema, matching the baseline for high schema coverage.

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 what the tool does: 'What is due at a stop and when.' It identifies the resource (a stop) and the output (arrivals/departures). While it doesn't explicitly distinguish from sibling tools like transit_nearby or transit_status, the purpose is specific enough to be understood.

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 explains how to use it ('Takes a stop name or an id') and provides context about data sources (live in London, timetable elsewhere). However, it does not explicitly state when to use this tool versus alternatives, nor does it mention exclusions or prerequisites.

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