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

Beyond the readOnly/idempotent/openWorld annotations, the description discloses that coordinates are sent to a third party (Transitous), that no API key is needed, that transit trips bundle walking to and from stops, and that omitting times means a leave-now request. The data-sharing disclosure is exactly the kind of behavioral context annotations cannot express.

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 output content is front-loaded in the first sentence and every remaining sentence carries a distinct instruction. The style is telegraphic and slightly fragmented ('Use coordinates from the selected search result.'), which reads as clipped rather than as a coherent guide, but there is no filler.

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?

With 8 parameters, nested coordinate objects, real geographic bounds, and no output schema, the description does the important work: it describes what a trip result contains and how to shape the time and mode inputs. The gap is the three undocumented optional parameters (limit, maxTransfers, wheelchair), which an agent must infer from names alone.

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 full explanatory burden. It does add real meaning for the time parameters (mutual exclusivity, mandatory UTC offset, default leave-now behavior) and for modes (walk/bicycle are alternatives to transit), but limit, maxTransfers, and especially the wheelchair accessibility flag are never mentioned despite being non-obvious to an agent.

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 — 'Find complete trips' — and enumerates what a result contains (walking, transit, transfers, scheduled and predicted times, total travel time). It also implicitly positions itself against search_places by telling the agent to 'Use coordinates from the selected search result', so the agent can tell which sibling supplies its input.

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?

It gives explicit conditional guidance: omit times to leave now, otherwise supply departureTime OR arrivalTime with a UTC offset; add walk or bicycle to modes to compare non-transit options. That covers the primary decision points an agent faces when choosing how to call this versus other routing or lookup tools.

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