decode_vinDecode a vehicle VIN. Decode VIN. Decode any 17-character VIN: make, model, model year, trim, body, engine, fuel, transmission, drive type and plant, plus check digit validation, region and country of manufacture. Always answers, even when the upstream registry is slow.
| Name | Required | Description | Default |
|---|---|---|---|
| vin | Yes | 17-character Vehicle Identification Number (e.g. 1HGCM82633A004352) |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so safety and external-dependency context is covered. The description adds a genuine behavioral trait beyond that – 'Always answers, even when the upstream registry is slow' – signaling latency/fallback behavior. It does not cover rate limits, error cases, or output format.
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 opening is padded with redundancy: 'Decode a vehicle VIN. Decode VIN.' says the same thing twice before any new information. The remainder is a dense, useful field list, but the front-loaded duplication costs efficiency.
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 description carries the return-value burden and does so well by enumerating decoded fields plus check-digit validation and origin data. It is complete for a one-parameter lookup tool, missing only edge-case behavior (invalid VIN handling).
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 the single 'vin' parameter is fully documented in the schema with an example. The description repeats the 17-character constraint but adds no syntax or format detail beyond what is already structured. 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?
States a specific verb ('Decode') and resource ('vehicle VIN'), then enumerates the exact fields returned (make, model, model year, trim, body, engine, fuel, transmission, drive type, plant). No sibling tool overlaps with VIN decoding, so no disambiguation is needed. An agent can confidently tell what this does.
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?
Usage is only implied by the tool's single purpose – there is no explicit 'use when' or 'do not use when', though with only one VIN-related sibling absent from the list, there is little to route between. The 17-character constraint hints at applicability but is not framed as guidance.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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