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FabTally Valid

by io.github.zvmzaretsky
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Decode a VIN via NHTSA vPIC (paid $0.002)

decode_vin

PAID $0.002 (x402, USDC on Base). Decode a Vehicle Identification Number: give {vin} and get a 17-char format + North-American check-digit validation and a full decode via NHTSA's public vPIC API — make, model, year, body class, engine, plant country and more. VIN-only (never plate→owner). Without payment returns the x402 challenge; pass x_payment to settle.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "vin": "<vin>"
    },
    "name": "decode_vin"
  }
}

Input Schema

NameRequiredDescriptionDefault
vinYesA 17-character Vehicle Identification Number (excludes I, O, Q).
x_paymentNox402 payment payload (base64) for this PAID validation. If supplied it is forwarded as the X-PAYMENT header to settle the call and return the real result instead of a 402 challenge. Omit to get the price challenge first.

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observed

TDQS

A4.2/5.0
Behavior4/5

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

No annotations are provided, so the description carries full responsibility. It discloses the paid nature ($0.002), the x402 payment mechanism, the fact that a challenge is returned without payment, and the VIN-only limitation. This goes beyond the minimum but does not cover rate limits or error behavior, which would be expected for a paid API.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is three sentences and front-loaded with the critical 'PAID $0.002' notice. Each sentence adds important information: the pricing/payment model, the core functionality and output examples, and the VIN-only restriction plus payment flow. No wasted words.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description must explain return values, and it does so by listing the validation and decode results. It covers the payment challenge behavior and the VIN-only scope. While it could mention error cases or rate limits, the provided context is sufficient for an agent to invoke the tool initially. A minor gap is not specifying the exact response format beyond examples.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The input schema already provides complete descriptions for both parameters (vin: 17-character VIN excluding I/O/Q; x_payment: base64 x402 payload forwarded as X-PAYMENT). The description adds examples of decode fields (make, model, year, etc.) but not new parameter-specific detail. Since 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.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool decodes a Vehicle Identification Number and lists the specific outputs (17-char format, check-digit validation, full decode via NHTSA vPIC API with make/model/year/body class/engine/etc.). It distinguishes this from sibling validation tools (VAT, IBAN, email, geo lookup) through the unique resource and API.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description explicitly notes the tool is VIN-only and never converts plates to owners, which sets a clear boundary. It also explains the payment flow (without payment returns an x402 challenge; pass x_payment to settle), giving practical usage context. However, it does not explicitly compare against sibling tools or mention alternative VIN services, though the context is sufficient.

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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