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

With no annotations, the description carries the full burden and does well: it discloses the static-plus-realtime merge, that realtime entries replace matching scheduled entries, and precisely how ambiguous stop ids fail (an error naming both matches rather than guessing). It omits error behavior for unknown stops and any note on data freshness or return format.

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?

Four sentences, front-loaded with the core action, and each sentence contributes (scope, data sources, disambiguation rule, failure mode). The naming of upstream feeds (BusTime, City of Hamilton feed) is slightly more detail than an agent needs to call the tool.

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 tool with no annotations and no output schema, the description covers invocation behavior well, including the tricky disambiguation case. The notable gap is return semantics — whether times are absolute or relative, and whether realtime vs scheduled status is flagged — which an agent must infer.

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 baseline is 3; the description earns above that by explaining the collision semantics behind agency and the exact failure mode when it is omitted. It adds nothing about limit behavior or what stop_id formats are accepted beyond the schema's search_stops reference.

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 ('Get the next departures for one stop') and scopes it to two named agencies (TTC, Hamilton HSR). It does not explicitly contrast itself with siblings like route_vehicles or service_alerts, so it falls short of the 5 bar, but the purpose is unambiguous.

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?

Gives an explicit conditional rule for the optional agency parameter (pass it when the stop id belongs to both agencies, otherwise a dual-match error results), which is real when-to-use guidance. It never names alternatives such as service_alerts for disruption info, so no exclusions are stated.

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