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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds genuinely new behavioral context: the underlying data source (NHTSA vPIC), a geographic coverage limitation, and a 5-credit cost — the kind of information an agent cannot get from structured fields.

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?

A single front-loaded sentence carries the verb, the resource, the full field list, the data source, the coverage caveat and the cost — with no boilerplate or repetition. Every clause earns its place.

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 field enumeration is the right compensation and is present; source, coverage limits and cost round it out. Minor gaps remain: nothing is said about failure behavior for an invalid or unknown VIN, and the schema marks vin as 'required' while the top-level required list is empty.

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% and both parameters are documented there, including the 17-character VIN format and the note that modelYear helps older VINs. The description adds nothing about parameter behavior beyond the schema, so the 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 verb (decode) and resource (VIN), then enumerates exactly what attributes are returned (make, model, year, trim, body, engine, transmission, plant, airbags, driver-assist). It is unambiguous about what the tool does, but it never references the sibling nl_vehicle, which an agent might reasonably confuse with a VIN decode.

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 explicit when-to-use or when-not-to-use statement. The caveat 'Fullest for North American vehicles' implicitly tells the agent when results will be weaker, and the '(cost: 5 credits)' note gives a cost-based selection signal, but neither is framed as guidance and no alternative tool is named.

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