transit_arrivals

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

Annotations already declare readOnlyHint=true, so the safe-read behavior is covered. The description adds useful context about system-specific station IDs and real-time data, but does not describe return format, error behavior, or rate limits. This is moderate extra value beyond annotations.

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 sentences, front-loads the action, lists systems in a compact list, and ends with a valuable note on station IDs. No redundant or wasteful text.

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?

The tool has only two parameters and the schema covers them well, but there is no output schema and the description does not explain what the returned arrivals data looks like or how to resolve station IDs for systems not given examples. This is adequate but has clear gaps for a complete picture.

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%, giving baseline 3. The description adds concrete examples of station ID formats (BART: EMBR, WMATA: A01, CTA: 40380), which helps the agent understand the system-specific nature beyond the generic schema text.

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 tool's function: 'Get real-time arrivals/predictions for any of 12 US transit systems,' with an explicit list of supported systems. This specific verb+resource+scope distinguishes it from single-system siblings like cta_train_arrivals or mbta_predictions.

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 usage for the listed systems but provides no guidance on when to prefer this tool over dedicated per-system siblings (e.g., trimet_arrivals, path_arrivals). It also does not mention how to discover system-specific station IDs, which is a key prerequisite.

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