list_supported_cities

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It accurately describes the content (cities, agencies, modes, capabilities) but does not mention the return format, whether the operation is read-only (though implied by 'lists'), or any potential pagination or limits. It covers the scope but lacks detail on output structure or edge cases.

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?

A single, front-loaded sentence that wastes no words. It leads with the core action and resource, and packall the key content into ~14 words. No redundancy or padding.

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 list tool with no parameters and no output schema, the description is nearly complete. It names all major categories of information returned (cities, agencies, modes, capabilities) and the scope (US transit). Minor gaps include the exact format of the response (e.g., list of objects vs. simple strings), but the description provides enough for an agent to invoke the tool without ambiguity.

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 tool has zero parameters, and the schema is an empty object, so there are no parameter semantics to document. The description does not need to elaborate on parameters, and the baseline for a zero-parameter tool is 4, which is appropriate here.

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 ('Lists') and names the exact resource ('supported US transit cities, transit agencies, modes, and feature capabilities'). It clearly differentiates from sibling tools like list_routes and get_departures, which target specific transit data rather than a broad catalog of supported locations and capabilities.

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?

Although the description does not explicitly state when to use this tool versus alternatives, the purpose itself implies it as a discovery tool—agents would call it before using sibling tools that require a city or agency context. No exclusions or conditions are provided, but the context is clear enough for an agent to infer its use case.

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