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

Annotations already establish read-only, open-world, idempotent, non-destructive behavior. The description adds real value beyond them by disclosing that the returned content is affiliate search handoff cards rather than live data or confirmed bookings — an important expectation-setting trait not captured by the annotations.

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?

Two tight sentences with zero padding; the core purpose is front-loaded and the caveat follows immediately.

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 no output schema, the description usefully characterizes what the tool returns (provider search handoff cards) so the agent knows not to treat results as live booking data. Combined with the rich parameter schema, this is nearly complete; only a clearer routing recommendation versus alternatives is missing.

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 all six parameters (including locale, trip_id currency defaults, and date formats) are fully documented in the schema. The description restates the pickup location and dates but adds no syntax or semantics beyond that, so the baseline of 3 applies.

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?

States a specific verb (Return) and resource (DiscoverCars and Expedia affiliate car-rental search cards) with scope (pickup city/airport + dates). It distinguishes itself clearly from the sibling booking-link tools (flight_booking_link, train_booking_link, ground_transfer_booking_links).

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 second sentence gives strong context on what this tool is not ('provider search handoffs only, not live availability, prices, vehicles, or confirmed bookings'), which steers the agent away from promising real prices. It does not, however, explicitly name an alternative to use when the user needs actual availability, so it falls short of a full when/when-not/alternative guide.

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