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

Annotations already mark it as read-only, idempotent, and non-destructive. The description adds important behavioral context beyond those annotations by stating it is keyless and that real-time data is provided only where the operator publishes it, which is a meaningful data-freshness caveat.

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 compact and front-loaded: it states the purpose first, then the required input, then the output contract, then the keyless/real-time caveat. Every sentence earns its place and there is no filler.

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 supplies a sufficient return-value contract by listing the exact fields the caller will receive. Input semantics are fully covered by the schema and examples, and the keyless/real-time caveats cover the operational essentials for a low-risk read-only call.

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 covers 100% of parameters with detailed descriptions, examples, defaults, and allowed mode values. The description mostly restates the id guidance already present in the schema, so it adds little new parameter-level meaning; the high schema coverage justifies the baseline score of 3.

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 names a specific resource — a live arrivals board for a German/European station — and lists the concrete return fields (line/train number, origin, scheduled/real-time arrival, delay, platform, operator). This clearly distinguishes it from sibling tools like dbrail_departures and dbrail_journeys.

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 gives clear context: call this tool when you need upcoming arrivals for a station, passing either a station name or a dbrail_locations stop id. It does not explicitly say 'use dbrail_departures for departures', but the arrival-specific framing and station-scope make appropriate usage clear, and no exclusion conditions are stated.

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