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

Annotations already declare readOnly/openWorld/non-destructive, and the description goes well beyond them: it discloses the candidates fallback for ambiguous names, the geometryDegraded and patternsTotal/matchedTotal semantics, unknown-place behavior, and a hallucination guardrail. Rich behavioral context for a read tool.

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 purpose and then grouped into required/optional/response/limits/not-for sections. It is dense and long, but nearly every sentence carries distinct information; the bolding and structuring keep it navigable rather than padded.

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 carries the full return-value burden and does so: it explains per-direction courses with headsign, halts, pathOnMap simplification, the candidates alternative, and the max ~50 m simplification with render_payload for full resolution. Nothing essential is missing.

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 already 100%, so the baseline is 3. The description still adds value by foregrounding the 'exactly one of query/id' obligation and the area/limit defaults, though it mostly reinforces rather than extends the schema wording.

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 opening states a specific resource (the halt sequence of an ÖPNV line and its drawn map path) and pairs it with concrete user questions ('wo fährt die Y entlang'). It also explicitly names the siblings it is not (connections, departures, disruptions), so an agent can route correctly without opening schemas.

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?

Gives an explicit when-to-use rule, the 'genau EINE Linie' constraint, the fallback when ambiguous (query by area or by id), and an explicit 'Nicht dafür' list mapping other needs to connections/departures/disruptions. Almost no inference is left.

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