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

Annotations provide no behavioral hints, so the description carries the full burden. It reveals the tool's read-only nature through phrases like “live departure or arrival board” and “From National Rail,” and further details returned fields: scheduled and expected time, platform, operator, destination, and disruption notices.

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: one defines the tool's core purpose, the second enumerates the key output fields. Every sentence adds value, and it is appropriately brief for a tool of this complexity.

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?

With no output schema, the description does a good job of explaining what results include: scheduled/expected times, platform, operator, destination, and disruption notices. It is sufficiently complete for a simple, well-parameterized lookup tool, though it omits edge cases like invalid station codes or default behavior.

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 schema already documents all three parameters with 100% description coverage, so the baseline is 3. The main description mostly reinforces station code and adds source context rather than new parameter-level meaning beyond the schema.

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 it is a live departure or arrival board for British railway stations using a three-letter station code, with specific reference to National Rail. This distinguishes it from bus and other transit tools in the sibling list, such as transit_buses.

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 clearly establishes a use context: train departures/arrivals at a British National Rail station by three-letter code. It does not explicitly mention alternatives or exclusions like “use transit_buses for buses,” but the context is clear enough to guide tool selection.

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