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

With no annotations provided, the description carries the transparency burden. It discloses the external data source (NHTSA vPIC), the per-call cost of $0.005 USDC, and the payment mechanism (x402 on Base), which are important behavioral facts beyond the tool's name. It does not mention failure modes or invalid VIN handling, but the disclosed cost and external dependency are significant and useful.

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 three sentences with no filler: first sentence states the action and output, second gives the use case, third states cost and payment method. It is front-loaded with the core purpose and every sentence 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 one-parameter read-only lookup tool, the description covers purpose, output fields, data source, cost, and usage context. The lack of an output schema is mitigated by the explicit list of decoded attributes, and no critical operational detail is missing for correct tool 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 single vin parameter is already fully described in the input schema, including length constraints (11-17 characters), required status, and an example. The description adds no new parameter-level semantics, but because schema coverage is 100%, 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?

The description states a specific verb ('Decode'), a precise resource (a VIN), and enumerates the exact output fields (make, model, model year, body class, engine, plant country). It also positions the tool relative to siblings by mentioning it is used 'before looking up recalls or bulletins', making it easy for an agent to distinguish from dtc_lookup, vehicle_recalls, and vehicle_tsbs.

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 gives explicit guidance: use this tool when you have a VIN and need to identify the exact vehicle before proceeding to recalls or bulletins. It does not explicitly state when not to use it or name alternative tools, but the context strongly implies the appropriate sequence among the siblings.

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