oba_arrivals

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

The readOnlyHint annotation already establishes a safe read operation. The description adds behavioral value by specifying that the tool returns predicted and scheduled times, route info, vehicle tracking, and distance from stop. This gives the agent a concrete sense of the response payload without needing an output schema.

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 sentences with no filler. It front-loads the action (Get real-time predictions), then details return contents and coverage, with each sentence contributing useful 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?

For a one-parameter read-only tool with a well-documented schema, the description is quite complete. It covers the purpose, geographic scope, agencies, and return contents. The only minor gap is the lack of explicit discussion of response structure or limitations, but that is not critical for invocation.

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 input schema already provides a full description for stop_id, including an example format ('1_75403'), achieving 100% schema description coverage. The tool description does not add parameter-specific details, but the baseline score of 3 is appropriate because the schema handles the semantics.

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 opens with a specific verb and resource: 'Get real-time arrival and departure predictions' for a transit stop. It further distinguishes itself by explicitly scoping to 'Puget Sound (Seattle area)' and listing the covered agencies, which differentiates it from sibling transit tools like CTA, MARTA, and SEPTA. The return contents are also summarized.

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 clear context by stating the geographic scope and transit agencies covered, making it evident when to use this tool. However, it does not explicitly mention alternatives or include 'when not to use' guidance, so it stops short of a 5.

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