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

Annotations already cover read-only, idempotent, non-destructive behavior, and the description adds what they cannot: the account-link and plate-unlock preconditions and an explicit 'never spends' credit guarantee. It doesn't mention rate limits or failure modes, but the cost/safety picture is notably enriched beyond 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 the purpose front-loaded and the constraints and output content following. Slightly dense in the second clause, but essentially zero waste.

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 an output schema present, return values needn't be explained, yet the description still sketches them helpfully. Prerequisites, cost behavior, and read-only status are all covered; only explicit sibling routing is absent.

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?

The single parameter is fully documented in the schema ('UK registration plate, any spacing or case'), so the baseline is 3. The description's only added meaning is the requirement that the plate be unlocked, which is useful but tied to state rather than parameter format.

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+resource ('Advice for viewing an unlocked car in person') and enumerates the payload ('a summary, priorities to check ... and known weak spots of the model'). This clearly separates it from siblings like full_report, compare_vehicles, or free_check without needing to open any 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 the operative context and prerequisites: it applies to an unlocked car and requires a linked account plus an unlocked plate, implying unlock_report/free_check must run first. It stops short of naming those sibling tools or stating when NOT to use this over alternatives, so it stays at 4 rather than 5.

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