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

With no annotations, the description carries the full burden: it usefully discloses the multi-agency merge behavior and that every result carries an agency field, which prevents misreading merged results. It does not cover whether the static feed data may be stale, ordering of results, or any auth/rate-limit considerations—moderate coverage for a read-only lookup.

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?

Three short sentences, front-loaded with what the tool does and followed by default/override behavior. The final sentence about the agency field is mildly redundant with the enum and could be folded in, but nothing is wasted at length.

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 three-parameter lookup with no output schema, the description supplies the essentials: data source, default scope, merge behavior, and a key return field. Left unstated are result ordering and the freshness caveat implicit in 'static GTFS feeds', which an agent might need when results look outdated.

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 query, agency, and limit are already documented including the enum and 1-50 bound. The description adds the meaningful behavioral detail that omitting agency merges both sources, but it introduces 'stop code' as a searchable key that the schema's query description omits ('stop number or part of a stop or station name'), creating a small mismatch rather than added clarity.

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 ('Find transit stops and stations') and names the search keys (stop number, stop code, name) plus the underlying source (static GTFS feeds). It is clearly distinguishable from siblings like next_departures and route_vehicles, which are real-time operational queries rather than static stop lookup.

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 clear default behavior ('searches both the TTC and Hamilton HSR by default and merges the results') and the condition for narrowing ('pass agency to search one agency only'). It lacks explicit exclusions or a pointer to the sibling tools for departure/vehicle/alert questions, so routing guidance is implied rather than stated.

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