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

Annotations already declare readOnlyHint/idempotentHint/destructiveHint, and the description goes well beyond them with rich behavioral context: the private-owner confirmation model, that price_day:null is normal rather than a data gap, that coordinates are deliberately approximate, and the hard privacy rule about phone/address/licence plate. These are actionable constraints an agent must follow when presenting results, and none contradict 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?

The description is long (~240 words) but organized into scannable labeled sections (CARS ON HOTELSCASA, PRICE, GOLDEN LINK RULE) and front-loaded with the core purpose. Every sentence carries a consequential operational rule rather than filler; it is only held back from 5 by some broader platform business context that is useful but not strictly required for invoking the tool.

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—output schema present, non-trivial interpretation pitfalls (null prices, approximate coordinates, busy_ranges semantics)—the description covers everything an agent needs: what the tool returns, how to interpret ambiguous values, the mandatory booking_link behavior, and privacy boundaries. The only minor omission is explicit sibling routing, but the output schema and annotations carry the structural weight, so nothing critical 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 coverage is 100%, so the baseline of 3 applies: lang, vehicle_id, pickup_date, and return_date are all already documented in the schema. The description adds only marginal input-parameter meaning by tying dates to total_eur ('the rental for the whole period'); its main parameter-related content concerns output fields like price_day and booking_link, which belong to the output schema's domain.

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 specifies a concrete verb and resource: 'Full details of ONE rental car' followed by an explicit inventory (photos, specs, rental conditions, busy_ranges). The singular 'ONE' and the enumerated contents distinguish it from search_vehicles (a listing tool) and check_vehicle_availability (a focused availability check).

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 explicit operational guidance: use busy_ranges to propose alternative dates, use booking_link to let travellers ask about unrated cars, and never call a price_day:null car unavailable. However, it never names the sibling tools as alternatives (e.g., 'to find cars, use search_vehicles'), so the when-to-use versus alternatives routing is implied rather than explicit.

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