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

Annotations already cover read-only, idempotent, and non-destructive behavior. The description adds valuable transparency by stating 'Keyless' (no auth requirement) and detailing the response contents: route options with duration, transfers, and per-leg scheduled plus real-time times. This goes beyond the annotations without contradicting them.

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 sentences with no filler: the main purpose is front-loaded, input style is illustrated with a compact example, output shape is summarized, and the keyless property is a single important word. Every sentence 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?

For a tool with no output schema, the description covers the essential context an agent needs: purpose, supported locations, input formats, response structure, and authentication requirement. The remaining specifics (default result count, date format, limits) are already fully documented in the input schema.

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% and the schema already explains all four parameters. The description reinforces that from/to accept station names or stop ids and narrows the geographic context to Europe, but it does not add significant operational meaning beyond the schema's existing parameter descriptions.

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 clearly identifies a specific action—planning multi-leg rail/public-transport journeys between two European places—and distinguishes this from the sibling timetable tools like dbrail_arrivals and dbrail_departures. It names the accepted input forms (station names or stop ids) and summarizes the output, leaving no ambiguity about what the tool does.

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 gives clear context for when to use the tool: between two places in Europe, for multi-leg route planning rather than single-station timetable checks. It does not explicitly name sibling alternatives or state exclusions, but the phrase 'multi-leg journey' and the route-option output make the usage context sufficiently clear.

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