transit_lines

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

Annotations already declare readOnlyHint=true and openWorldHint=true, covering safety and non-exhaustive nature. The description adds 'canonical ids' as useful context, indicating the output is a set of identifiers, but it does not describe the response structure or further limitations beyond what annotations provide.

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?

Two short, front-loaded sentences with no filler. The phrase 'Directory of...' immediately conveys the resource, and the second sentence gives a direct action. Every word earns its place.

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 the tool's simplicity (no parameters, read-only), the description covers the core purpose and usage effectively. Without an output schema, it could mention the response format (e.g., list of lines with IDs), but the current text is adequate for discovering line identifiers.

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 0 parameters, so the schema provides no parameter details. According to the baseline for 0-parameter tools, a score of 4 is appropriate; the description does not need to explain parameters.

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 identifies the tool as a directory of Japanese rail operators and lines with canonical IDs, and explicitly states its purpose: to discover valid line identifiers. This distinguishes it from sibling tools like transit_line_disruptions or transit_route_plan, which focus on status or routing.

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 a clear usage context ('Use to discover valid line identifiers'), implying this is the reference/lookup tool among transit siblings. However, it does not explicitly mention when not to use it or name alternative tools for related needs, such as station lookup.

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