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

Annotations already cover read-only and idempotency, and the description adds substantive context beyond them: the RDW data source, the paid model (0.004 USDC via x402 or 2 credits), and the free tier (first 5 paid calls per day). It also discloses the comparison-specific output traits (best per metric, red flags) that no structured field carries.

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-loaded with the 'Use when' trigger, followed by output, input, source, and cost in a tight single paragraph with no filler. The long metric enumeration is justified because no output schema exists, though it is denser than strictly needed.

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 one parameter fully described, no output schema, and annotations covering safety, the description fills the remaining gaps: return contents, data source, and payment/credential requirements. An agent has everything needed to call it and set user expectations about cost.

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% and the schema itself documents the semicolon-separated plate format with an example. The description only restates 'Input: Dutch licence plates' plus the 2-3 count already implied by the concept, adding no syntax or format detail beyond the schema.

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 scope ('choosing between 2 or 3 Dutch used cars') and enumerates the compared metrics, so an agent knows exactly what comes back. It does not name any sibling (e.g. nl_vehicle_report for a single car), so differentiation from the other vehicle tools is left to inference.

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?

'Use when the user is choosing between 2 or 3 Dutch used cars' is a clear, concrete trigger condition. There is no explicit when-not guidance or named alternative for single-vehicle lookups, which the sibling set makes a real gap.

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