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

With no annotations, the description carries the burden and does disclose meaningful behavior: the result echoes searched_from, which should be surfaced as a changeable assumption, and known error codes have a prescribed handling path. It leaves the side-effect profile (read-only) and result breadth implicit, so it is strong but not complete.

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-loads the core capability, then layers required-parameter and error-handling instructions in short sentences that each carry operational value. Slightly dense but 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?

For a five-parameter search tool with no output schema, the description covers the critical unknowns: the mandatory duration, the assumption surfaced via searched_from, and the error path. Enum semantics for category/currency/language are left entirely to the schema, which is acceptable at 100% coverage.

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 five parameters are already documented in the input schema, which sets the baseline at 3. The description reinforces the required duration_days and the omit-to-search-from-now behavior of earliest_pickup_at, but adds no new meaning for category, currency, or language.

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 and resource — finds the soonest window a rental car is free for a given number of days — with the search origin defined (now or an optional earliest pickup). This scope is distinct from check_car_availability, though the description never names that sibling to make the contrast explicit.

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 concrete procedural guidance: duration_days is required and the agent should ask the person if unstated, and on an error code such as earliest_in_past it should relay the reason and ask again rather than guessing a date. It stops short of naming when to prefer a sibling tool over this one.

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