md_transit_vehicles

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

Annotations already provide readOnlyHint=true, so the description only needs to add context. It discloses the API key requirement and the list of agencies, which is useful. However, it does not mention response format, data freshness, error behavior, or rate limits, leaving some behavioral gaps.

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 three concise lines, front-loaded with the main action, and includes the key requirement and agency mapping. Every sentence earns its place; no filler or redundancy.

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 single-parameter read-only tool, the description covers the essential aspects: what it does, the required environment variable, and the accepted agency values. Since there is no output schema, a brief note on the expected response structure would have made it complete, but it is already quite usable.

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 adds value by mapping each enum value to its human-readable agency name (e.g., 'mta-maryland' = Local Bus), which helps agents select the correct parameter. This goes beyond the schema's 'Swiftly agency key'.

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 uses a specific verb 'Get real-time vehicle positions' with a clear resource 'Maryland MTA transit'. It lists the four agency keys with human-readable labels, which makes the tool's scope unmistakable and distinguishes it from other transit tools like md_transit_trip_updates.

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 implies the primary use case (retrieving vehicle positions) and notes the required API key, but it does not explicitly contrast this tool with siblings like md_transit_feeds or md_transit_trip_updates, nor does it state when not to use it. Usage is reasonably clear but lacks explicit alternative guidance.

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