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

Annotations already declare readOnly, idempotent, non-destructive, closed-world, so the safety profile needs no restating. The description adds genuine behavioral context: the data source is live RDW Open Data, one input unlocks the extra bijtelling block, and the electric rate is locked for 60 months from first registration.

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?

One dense paragraph, front-loaded with the core lookup before the conditional bijtelling behaviour and the data-source note. The field enumeration is a long list but each item is a distinct return value, so little is wasted.

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 correctly carries the return-value burden by enumerating the fields produced. Only gaps are failure behaviour for an unknown plate and whether partial or missing RDW records are possible.

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%, so the baseline is 3. The description nevertheless adds meaning beyond the schema: it explains the causal effect of supplying taxable_income and the 2026/60-month rule attached to it, and confirms plate accepts the dashed or undashed kenteken form.

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 (lookup Dutch-registered car by kenteken) and enumerates the exact fields returned, including APK due date, insured status, and conditional bijtelling. An agent knows precisely what this does and what comes back without opening anything else.

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 description makes clear this is a per-plate RDW registry lookup and that taxable_income is only needed when company car tax is wanted, which is actionable usage context. It does not name exclusions or point to alternatives, though the sibling tools (budget, facts, rent points) are unrelated domains so there is little routing ambiguity.

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