sg_bus_arrival

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

No annotations are provided, so the description carries the full burden. It discloses the authentication requirement (SG_LTA_KEY) and a behavior (shows next 3 buses per service), which are useful beyond the schema. It doesn't cover all edge cases, but for a read-only tool this is sufficient.

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 concise sentences: first states the primary purpose and output limit, second gives key requirement and practical examples. No filler, all information is high-value and front-loaded.

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 tool with two parameters and no output schema, the description explains the output ('next 3 buses per service') and required key. It could add more detail about the exact response structure, but given low complexity, this is adequately complete.

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 covers 100% of parameters with descriptions, so baseline is 3. The description adds value by providing concrete example values for bus_stop_code (83139, 46009), which aids in selecting real stops. It doesn't deeply elaborate on service_no, but the schema already explains it as an optional filter.

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 a specific action ('Get real-time bus arrival times at a bus stop') and differentiates from sibling tools by specifying the resource (bus arrivals) and output scope (next 3 buses per service). This immediately distinguishes it from MRT, taxi, and other transport tools.

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 for use: real-time bus arrival times, with a required API key and common bus stop examples. It does not explicitly mention when not to use it or name alternatives, but the resource specificity makes the usage context clear enough without needing explicit exclusions.

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