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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the description does not need to repeat that. It adds that the tool returns 'current status and running position details,' which is useful, but it does not disclose any limitations, error conditions, or the fact that journey_date is ignored (though that appears in the schema). Overall, it provides some value beyond annotations but is not particularly rich.

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 sentences, front-loaded with usage instruction, and contains zero filler. Every word contributes to clarity, making it appropriately concise.

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 (2 params, 1 required, has output schema) and strong annotations/schema, the description is nearly complete. It does not mention that journey_date is ignored, but that information is in the schema. It clearly defines what to expect in return, so it is sufficiently complete for a straightforward read-only API.

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 description coverage is 100%, so the schema already documents both parameters effectively. The description does not add any parameter-specific meaning beyond what the schema provides; it only mentions 'known train number' which essentially restates the train_number parameter. Baseline 3 applies due to high coverage.

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 explicitly states the tool's purpose: to provide current running status/location for a known train number. It specifies the endpoint and the returned information, distinguishing it clearly from sibling tools like station live boards or route inquiries.

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 first sentence gives a clear directive: 'Use this tool when the user wants current running status/location for a known train number.' This provides explicit usage context, though it does not mention alternatives or when NOT to use it, so it loses a point for lacking exclusions.

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