plan_journey

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

With no annotations provided, the description carries the full behavioral burden. It discloses meaningful operational traits: results are ordered fastest-first, cross-London transfers are approximate walk/Tube links, live Darwin times are only added for today's trains within the next two hours, and at-risk connections are flagged. This goes beyond a typical terse description, though it does not address read-only/side-effect behavior explicitly.

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, each earning its place: the core purpose, the output ordering and approximation caveat, and the live-data behavior. It is front-loaded with the most decision-relevant information and contains 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 the tool's complexity, the description covers the essential choices an agent must make: output ordering, change limits, cross-London transfer approximations, and live data conditions. The presence of an output schema relieves the description of explaining return fields in detail. It is slightly incomplete only in not clarifying count's meaning and not naming sibling alternatives, but it is otherwise robust.

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 75%, so most parameters are already documented. The description adds useful prose meaning for max_changes and live, but count remains undocumented in both the schema and the description, leaving its role as the number of returned journey options implicit rather than explicit. This partial compensation keeps it at the baseline rather than above it.

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 opens with a specific verb and resource: 'Plan journeys between two stations, with changes up to max_changes.' It also states the output ordering and the fewest-changes option, clearly differentiating it from sibling tools like live_departures and timetable, which cover station departures or single services rather than end-to-end journey planning.

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: use this tool when a journey between two stations is needed, including changes and cross-London transfers. It does not explicitly name alternatives or state when not to use it, so it stops short of the highest bar, but the intended use case is unmistakable.

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