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

Annotations already declare read-only, idempotent, non-destructive and closed-world, so safety is covered. The description adds genuinely new behavior: ids expire after 72 hours, the response includes a booking link and an .ics calendar file, and the widget renders every leg — all of which shape how the agent should reply.

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 returns, then usage, then response formatting — a sensible order with no filler sentences. It is dense for a single paragraph and the reply-length/widget instructions could be separated, but every clause carries information.

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?

There is no output schema, yet the description fully describes the return: a leg-by-leg itinerary with local times, a booking link, and a downloadable .ics. Combined with the 72-hour id lifetime and the widget-rendering note, an agent has everything needed to call it and respond correctly.

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 shows the id format, so the baseline is met by structure alone. The description adds real meaning by tying the value to a find_trips row id or the top pick, which is not expressed in the 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?

Names a specific verb and resource ('Shows one trip ... step by step, door to door') and enumerates the itinerary contents — home departure, transit to airport, airport wait, flight, city transfer, return — which clearly separates it from find_trips, which finds rather than details a trip.

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?

Explicit when-to-use: 'when the user picks a trip or asks how the journey works', plus how to source the id from the find_trips answer including the 'best one' shorthand. It also adds a negative instruction not to consult external flight/airport/transit sources, which removes a plausible wrong path.

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