la_metro_vehicles

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

The readOnlyHint annotation already indicates this is safe to call. The description adds that it returns real-time positions for all active vehicles and lists the included data fields (GPS coordinates, route, trip, stop, status), which provides some behavioral context beyond the annotation. However, it does not disclose any potential limitations such as pagination, latency, or data availability, so it only partially goes beyond the annotation.

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 long, with the first sentence stating the primary purpose and the second listing the return fields. It is front-loaded, concise, and contains no superfluous information.

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 and no parameters, the description must convey what the agent can expect. It lists the key return elements (GPS coordinates, route, trip, stop, status) and specifies that it covers both buses and rail. It could be slightly more complete by describing the response format (e.g., list of vehicles), but it is sufficient for a simple no-parameter tool.

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?

The tool has zero parameters, and the schema is empty. The description correctly implies that no arguments are needed by stating it returns data for 'all active vehicles'. Since there are no parameters to explain, this dimension gets a baseline of 4, and the description handles it well without adding unnecessary parameter details.

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 the specific action ('Get real-time bus and rail vehicle positions') and the target resource ('for LA Metro (Los Angeles)'). It distinguishes from sibling tools like la_metro_routes and la_metro_stops by focusing on vehicle positions, and from other transit tools by naming LA Metro.

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 provides no guidance on when to use this tool versus alternatives. It does not mention any exclusions, prerequisites, or comparisons to related tools like la_metro_routes or mbta_vehicles. The only implicit hint is that it is for real-time positions, but no explicit usage context is given.

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