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

Annotations already mark the tool as read-only, idempotent, and non-destructive. The description adds valuable operational context beyond those annotations: external source (NHTSA vPIC), cost ($0.01 per call), and HTTP method (GET). This helps an agent understand dependencies and side effects.

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?

The description is a compact single line that front-loads the core purpose before adding source and pricing details. The opening 'VIN decode' is slightly redundant with the title, but otherwise every element 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?

For a simple two-parameter read-only endpoint, the description provides essential context: purpose, market scope, source, price, and endpoint. It omits return-value details, but the absence of an output schema and the straightforward decode operation make the definition sufficient for correct selection and invocation.

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?

The input schema fully documents both parameters with 100% coverage, including vin format/example and year as a model-year hint. The description adds no additional parameter-level meaning, so the baseline of 3 is appropriate.

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 ('Decode') and a specific resource ('US-market Vehicle Identification Number'), and adds the data source (NHTSA vPIC). No sibling tool overlaps with VIN decoding, so the purpose is unambiguous and the tool stands out at a glance.

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 clearly sets the target scope ('US-market') and the operation (decode), which tells an agent when this tool applies. It does not explicitly name alternatives or exclusion conditions, but the unique domain and stated source give sufficient context for selection.

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