plan_journey

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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. Beyond that the description adds genuinely useful disclosure: at most 3 options returned, the shape of each option (duration, transfers, step list) and that departure_time defaults to now in Paris local time. It says nothing about real-time versus scheduled data, ambiguous place-name handling, or error behavior.

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 what the tool does, then when to use it, then what it returns, then the arguments — a logical order with no filler sentences. The example values inside the Args block are doing real work rather than padding.

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 three-parameter tool with no output schema, the description covers inputs, defaults and the return shape, so an agent can call it confidently. The gap is behavioral edge cases: routing ambiguity resolution, real-time versus timetable data, and how it relates to the disruption sibling.

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 0%, so the description carries the whole burden and does so well: from_place is defined as station name, address, landmark or a stop ID from search_stop, with examples; to_place inherits those formats; departure_time is documented as optional with both accepted formats and a 'defaults to now' rule. That fully compensates for the empty 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 opening sentence names a specific verb and resource ('Plan a public transport journey') and pins the geographic scope to Île-de-France. That is enough to separate it from siblings like search_stop, next_departures and traffic_disruptions without opening any schema.

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?

Real user phrasings ('How do I get from X to Y?', 'Fastest way to Orly from Bastille at 18:00?') make the intended trigger concrete. It stops short of naming alternatives — nothing says to use next_departures for a single stop's real-time board or traffic_disruptions for network status — so there is no explicit exclusion rule.

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