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

Annotations already establish readOnly, idempotent, non-destructive, open-world, so the description only needs to add operational detail — and it does: broken equipment listed first, a hard cap of 50, silent disambiguation when a name matches several stations, step-free surveys only where one exists for non-rail stops, and the instruction to surface an attribution line. That is material behavior an agent cannot infer from structured fields.

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?

Front-loaded with the capability, then triggers, then exclusions — a sensible order, and the quoted example utterances do real routing work. It is dense and occasionally repetitive (the 50-item cap and broken-first ordering appear in both description and schema), but no sentence is 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?

For a five-parameter read tool with no output schema, the description supplies what is missing: what an entry contains (place, state, reason), ordering and coverage guarantees, ambiguity handling, and the bilingual/attribution obligations. Nothing an agent needs to call it correctly is absent.

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% and the schema already explains limit ordering, eva_no exactness, station-versus-eva_no exclusivity, the facility filter rationale and the language default. The description restates the 50 cap and 'broken first', adding little parameter-level meaning beyond what the schema provides, so the baseline 3 applies.

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 concrete verb and resource — reporting whether lifts and escalators at a railway station or Köln Stadtbahn stop are working, each with place, state and reason — and explicitly contrasts itself with get_train_departures, get_departures and describe_station. An agent can route on it without opening any schema.

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 gives positive triggers (step-free access, broken lifts, wheelchair, pram) with quoted example queries in German and English, explicit exclusions (departures, platforms, delays, whole-station overview) and the sibling to use for each. The distinction between a railway/Köln Stadtbahn stop and other tram/U-Bahn/bus stops is also stated.

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