Cheapest fares across a day

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

Annotations already declare readOnlyHint, openWorldHint, and idempotentHint, covering safety and repeatability. The description adds useful behavioral context: results are organized by discrete time bands, include the applicable connection, and are most meaningful for long-distance advance bookings. It does not contradict the annotations.

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 with the core behavior, then gives a usage cue and an applicability caveat. The opening German word 'Bestpreissuche' is somewhat redundant and could confuse an English-only agent, but the rest of the description earns its place.

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?

The core behavior, use case, and a practical limitation are clear, and the output schema covers return shape. However, with eight parameters and very low schema coverage, the description does not compensate for missing guidance on optional parameters, station input format, or how filters like regional_only affect the search.

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 only 13%, and the description provides no parameter-level guidance beyond the implicit from/to/date purpose. Optional parameters such as bahncard, first_class, children_ages, and regional_only are left entirely unexplained in both the description and the 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 states a specific operation: find the cheapest available fare in each time band of a day, including the connection it applies to. This clearly distinguishes it from sibling tools like db_journeys or db_departures, which focus on journey listings or departures rather than cheapest fares by time band.

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 explicitly says to use this tool for 'when is it cheapest to go' and notes it is typically only meaningful for long-distance routes booked in advance. However, it does not explicitly name alternatives or state when not to use this tool versus sibling tools like db_journey_offers.

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