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

Beyond the readOnlyHint/idempotentHint annotations, the description discloses no-auth requirements, a 100 req/min rate limit, and that the data comes from a community HAFAS wrapper over BVG. This gives operational context that annotations cannot express and contradicts nothing in the structured metadata.

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 short sentences, with the core action front-loaded and every subsequent sentence adding a distinct fact: stop ID source, data provider, and auth/rate-limit context. No filler or repetition.

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?

Given a complete parameter schema, an existing output schema, and safety annotations, the description supplies the remaining needed context: how to obtain the required stop_id, geographic scope, auth, and rate limits. An agent has everything it needs to select and invoke the tool correctly.

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 coverage is 100%, so the baseline is 3, but the description adds value by giving the correct tool names for sourcing stop_id and framing the request as a time-window lookup. It also helps correct the schema's less precise reference to 'transport-rest.location_search'.

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?

Opens with a specific verb and resource ('Get real-time upcoming departures') and enumerates the returned fields (line, direction, platform, delay), so an agent can distinguish it from stop-discovery tools like search_locations and from journey planning. Geographic scoping to Berlin/Brandenburg further sharpens the purpose.

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 tells the agent that stop_id must come from transport-rest.transit.search_locations or transport-rest.transit.nearby_stops, establishing the correct pipeline before calling. It does not explicitly contrast with plan_journey or state when not to use it, so it earns 4 rather than 5.

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