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

Annotations already indicate readOnly, openWorld, idempotent, and non-destructive behavior. The description adds valuable behavioral details: data is live, includes crowding estimates, and legacy trolley numbers are auto-translated. No contradictions with 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 extremely concise: two sentences plus an example call. It front-loads the core purpose and data returned, with every sentence adding necessary information. No fluff 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?

Given there is no output schema, the description compensates by listing all key return fields (direction, destination, next stop, etc.). It adequately covers the input and provides examples. Minor omission: no mention of error handling or data freshness guarantee, but overall complete for a simple read-only 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 schema covers 100% of the parameter with a clear description and examples. The description adds extra semantic detail by explaining auto-translation of legacy trolley numbers and reinforcing the accepted route formats, providing value beyond the schema.

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 purpose: live SEPTA bus/trolley vehicle positions for a given route. It specifies the exact data returned (direction, destination, next stop, etc.) and distinguishes from sibling tools (e.g., septa_alerts, septa_next_to_arrive) by focusing on positions rather than alerts or arrivals.

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 when to use the tool (for live vehicle positions) and gives examples. However, it does not explicitly explain when not to use it or contrast with alternatives (like septa_next_to_arrive for arrival times). The sibling tools are listed but not referenced in the description.

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