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

Annotations already cover readOnly/idempotent/non-destructive, yet the description adds substantial non-obvious behavior: instant:true vs. owner-confirmed booking, similar_model guaranteeing class not model, price_day:null being normal rather than unavailable, the mandatory verbatim booking_link, and the prohibition on inventing phone/address/plate plus deliberately approximate coordinates.

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?

Long but front-loaded with purpose and exclusion before the labeled CARS/PRICE/GOLDEN LINK/NEVER blocks; each block carries operational rules an agent would otherwise get wrong. Some repetition (price rules restated in both prose and schema descriptions) slightly dilutes it.

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 16 optional parameters, an output schema, and full read-only annotations, the description supplies everything needed to call and present results correctly, including field-level interpretation (price_day vs total_eur) and the mandatory booking_link handling. Nothing material 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 88%, so the baseline is 3, but the description adds real semantics beyond the schema: price_min/price_max keep cars without a published rate, lat/lng drive the radius search, and radius_km/pickup_date/return_date are contextualized by the prose about rates and periods. It stops short of explaining page_token or query syntax.

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 (Search) and resource (RENTAL CARS) with the searchable dimensions listed (city, country, radius, dates, seats, transmission, class, price). It explicitly separates cars from properties, so an agent can distinguish it from search_properties/search_hotels without opening a 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?

Gives an explicit when ('traveller asks about a car') and when-not ('never to answer an accommodation question'), which routes the agent away from the accommodation siblings. The only minor gap is that it does not name search_properties/search_hotels verbatim, but the exclusion is unambiguous.

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