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

With no annotations, the description is the sole source of behavioral context. It discloses that only real data is returned and that transfer options are suggested when direct routes are unavailable, which is useful. However, it does not explicitly state read-only semantics, auth expectations, rate limits, error behavior, or what happens with invalid inputs.

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 a compact two-sentence structure with a dense list that front-loads the tool's coverage and a second sentence stating the real-data guarantee and fallback. Every clause serves a purpose, though a list of eight items makes it slightly heavier than the most minimal focused descriptions.

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 description covers the essential output facets (prices, trip counts, schedule, duration, stations, carriers, link) and the direct/no-direct fallback, which is enough given there is no output schema. It is slightly thin on edge cases (ambiguous city names, empty result behavior, and date edge cases, though the latter is covered by 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 description coverage is 100%, so the baseline is 3. The description details output fields but does not expand on parameter semantics beyond the inline schema descriptions that already name from/to as city name/slug and define date handling. No additional meaning is added for the parameters.

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 enumerates the route data that the tool returns (prices, number of trips, departure times, days, duration, stations, carriers, purchase link) and includes a distinctive fallback for cases without direct routes. However, it does not explicitly differentiate this tool from sibling tools like search_routes or find_transfer, even though the transfer fallback could overlap with find_transfer.

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 provides no guidance on when to use this tool versus alternatives. It does not mention city_departures or search_routes as options for overlapping use cases, nor does it state exclusions or prerequisites. The only conditional behavior ('if no direct flights, will offer a transfer') is a feature note, not a usage directive.

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