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

Annotations already declare readOnlyHint=true, openWorldHint=true, and idempotentHint=true, so the safety profile is covered. The description adds behavioral value by listing the specific decoded attributes (engine, drivetrain, transmission, body, fuel type) and claiming 'Full spec,' which goes beyond the annotations. It does not mention response format or error handling, but these are not critical given the annotations and schema coverage.

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 concise and front-loaded: the first sentence states the purpose and outputs, the second provides a concrete example. Every sentence earns its place with no filler or redundancy. The example is compact and directly illustrates usage.

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 read-only lookup with fully documented parameters and annotations, the description covers the essential return content (year/make/model/trim plus engine, drivetrain, transmission, body, fuel type) and provides a usage example. It does not describe the JSON structure or error scenarios, but these are not explicitly required for this tool type. A 4 reflects that it is nearly complete but omits potential edge-case guidance (e.g., invalid VIN behavior).

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%, with each parameter (vin, _apiKey, deepdata) fully documented in the input schema. The description adds little new parameter meaning beyond the example, which also appears in the schema. The mention of '17-char VIN' is redundant with the schema. Baseline 3 is correct because the schema carries the descriptive load.

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 clearly states a specific action and resource: 'decode a 17-char VIN into year/make/model/trim plus engine, drivetrain, transmission, body and fuel type.' It names the exact output fields and distinguishes itself from sibling tools like carsxe_plate_decode (license plate) and carsxe_market_value (valuation) by focusing on VIN decoding. The verb 'decode' is precise and matches the title.

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 provides clear context for when to use the tool (to get a full spec for a VIN) and includes a concrete invocation example. It does not explicitly mention related tools or exclusions, but the resource type (VIN) and output fields make the intended use unambiguous. A 4 is appropriate because context is clear without explicit alternatives.

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