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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint, so the safety profile is fully covered. The description adds source authority (Danish Motor Register) and that an 'odometer analysis' and 'inspection summary' are computed rather than raw, which is modestly useful. It says nothing about behavior on unknown plates, coverage limits, or why the call is open-world.

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?

It is one short sentence with no filler, which is good, but it is spent almost entirely enumerating return fields that the existing output schema already documents. The space would have been better used on the lookup action and the sibling distinction.

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, full param coverage and complete annotations, most structural burden is carried elsewhere, and the description need not re-explain return values. The remaining gap is routing: an agent cannot tell from this text why it should pick vehicle_lookup over vehicle_checks, which is the one thing the description should uniquely supply.

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?

There is a single parameter at 100% schema coverage, so the schema already explains that plate_or_vin accepts either a Danish number plate or a VIN/stelnummer, with an example. The description adds no semantics about the key; its field list concerns output, not input, so 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?

The description names a specific resource (vehicle data from the Danish Motor Register) and enumerates the fields returned, so an agent can infer what it gets back. But it never states an action verb or the lookup key — 'look up a vehicle by plate or VIN' only appears in the title and parameter name — and it does nothing to distinguish itself from the sibling vehicle_checks.

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?

There is no when-to-use guidance at all: no prerequisites, no mention of what input format to prefer, and no reference to alternatives such as vehicle_checks or phone_lookup. The agent is left to infer usage entirely from the name and schema.

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