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

Annotations already declare readOnlyHint=true and destructiveHint=false. The description adds valuable context beyond annotations by revealing the actual API endpoint and usage restrictions (India-only, date window), which helps an agent predict behavior without repeating annotation info.

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 sentences, zero fluff. First sentence states exactly when to use, second sentence lists exclusions. Every word earns its place; no redundant information.

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 read-only search tool with only 3 params and an output schema, the description covers all key aspects: purpose, endpoint, and exclusions. It doesn't need to describe return values since an output schema exists. The only minor gap is not explicitly stating the response is a list of trains, but that's implied by the name and schema.

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%—all three parameters have clear descriptions and examples. The description text doesn't add any parameter-specific details beyond the schema, which is fine since the schema is self-explanatory. Baseline 3 is appropriate.

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 does 'date-based route search when source, destination, and journey date are known' and even names the underlying endpoint. It distinguishes itself from siblings by focusing on the route-date search use case and explicitly excluding non-India routes, booking/payment, and future dates beyond 60 days.

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?

It explicitly states when to use ('when source, destination, and journey date are known') and gives three clear negative constraints ('Do not use for non-India routes, booking/payment requests, or dates beyond 60 days'). This effectively tells an agent when NOT to invoke this tool, even though it doesn't name alternative tools.

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