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

Annotations only declare it is a safe idempotent read; the description adds genuinely new behavior: the RDW source, the English output language, the exact cost model and credit conversion, and the free-tier carve-out that removes a payment blocker. That is precisely the context an agent needs before spending money.

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 usage trigger, then the payload contents, then input/source/cost — a sensible order with no filler sentences. The long field enumeration is dense but each item is informative; the 'in English' clause is awkwardly spliced into the list.

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 no output schema, the description carries the burden of describing return content and does so thoroughly, plus source, cost and payment paths. Minor gaps: no mention of error behavior for an unknown or non-Dutch plate, and no indication of response shape or latency.

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 both parameters are documented in the schema, including the fl_live_ format and the 'pass it right after get_trial_key' hint. The description only restates 'Input: Dutch licence plate', adding no syntax or format detail beyond the schema example GT-722-F.

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 ('report on a specific Dutch car or licence plate') and enumerates the returned data (APK expiry, inspection history, recalls, odometer verdict, specs, CO2, risk flags), so an agent knows exactly what it gets. It does not, however, distinguish itself from close siblings such as nl_vehicle_basic or buy_full_vehicle_report, which appear to overlap.

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 asks about a specific Dutch car or licence plate, for example before buying it used' gives a clear trigger scenario. Payment routing is also spelled out (0.02 USDC via x402, 10 credits, first 5 paid calls/day free), but there is no guidance on when to prefer the cheaper/sibling variants instead.

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