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

Annotations only cover the safety profile (readOnly, idempotent, non-destructive, openWorld). The description adds the details annotations cannot: pricing (0.001 USDC via x402 or 1 credit), the free tier of 5 paid-tool calls per day, the data source (RDW), and the shape of the returned status bands. That is exactly the auth/cost/rate context the annotations leave out.

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?

Trigger condition is front-loaded, followed by return payload, then input, then cost — a sensible ordering with no filler. Every clause (status bands, fleet polling, free tier) carries actionable information for an agent deciding whether to call.

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 compensates by enumerating the return fields and status bands, and it covers the payment/key path that a paid x402 tool requires. For a two-parameter, non-destructive lookup, nothing an agent needs before calling 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 description coverage is 100%, so both parameters are already documented in the schema, including the api_key flow. The description only restates 'Input: Dutch licence plate' and never mentions api_key, so it adds essentially nothing beyond the structured fields. Baseline 3 applies.

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 — 'when a Dutch car's APK (MOT) expires or whether it is still valid' — and enumerates the returned fields (expiry date, days left, status band, insurance and recall flags). This clearly separates it from broader siblings like nl_vehicle_report or buy_full_vehicle_report.

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?

The opening clause gives an explicit trigger condition ('Use when the user asks when a Dutch car's APK expires') and adds a legitimate secondary use case ('cheap enough to run daily for a fleet'). It stops short of naming alternatives or exclusions — it never says when to prefer nl_vehicle_basic or nl_vehicle_report instead.

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