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

Annotations already establish read-only, idempotent, open-world, non-destructive behavior, so the description's added facts are the valuable part: results come from a cache, are capped at 20, and cold caches cause unavailability rather than a fresh fetch. The attribution/freshness requirement signals downstream obligations beyond the annotation set, though the failure mode (error vs. empty result) is not spelled out.

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 short sentences with the operation and its cap front-loaded, followed by the caching and obligation caveat; there is no filler. The closing phrase 'preserve freshness, coverage and attribution' is compressed to the point of being under-specified, which is the only structural weakness.

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 one-parameter read with no output schema, the definition covers source (cache), volume (20 max) and a hard availability limit, which is reasonable. It omits what the agent should expect when the cache is cold (error message vs. empty list) and never clarifies whether the attributed data may be reshown, leaving a real gap for a low-complexity tool.

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?

With a single parameter and 100% schema description coverage including the pointer to list_stations for the catalogue, the schema already carries the semantics. The description adds nothing about accepted station formats or catalogue constraints, so this sits at the baseline for a well-documented 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 gives a specific verb and resource ('Read up to 20 eligible departures from a cached board') plus an explicit result cap, so the operation is unambiguous. It does not name or differentiate itself from siblings like next_train or platform_for, but the bulk-list framing distinguishes it implicitly from a single-next-train lookup.

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 clause 'Cold caches are unavailable' implies a precondition and effectively a when-not condition, but it does not route the agent to any alternative for a cold-cache station. The remaining guidance ('preserve freshness, coverage and attribution') reads as a data-license obligation rather than a usage rule, leaving the when-to-use decision partly inferred.

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