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

Annotations already declare read-only, idempotent, and closed-world behavior. The description adds meaningful detail beyond that: results are in departure order, contain scheduled times only (not real-time), and represent the full enquiry board for the station.

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?

Three tight sentences deliver purpose, ordering, scope, and the key alternative. The core meaning is front-loaded and every clause 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?

For a simple read-only listing tool, the description fully covers what it returns, how results are ordered, what data they contain, and when to choose it over the main sibling. No output schema exists, but the return semantics are sufficiently described.

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 input schema already documents station_code and after with descriptions, and limit has clear defaults and bounds. The tool description does not add parameter-specific detail, so it neither compensates for nor harms the 67% schema 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 states exactly what the tool returns: every scheduled train at a station in departure order. It also distinguishes itself from a journey plan and from plan_journey, making its purpose unambiguous.

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 gives the decision rule: use plan_journey when the user wants to reach a destination, use station_departures when asking what leaves from this station. This is concrete, actionable guidance that prevents mis-selection.

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