veridigit

Verified validation of structured identifiers for AI agents — checksums, not guesses.

LLMs cheerfully accept malformed IBANs, mistype card check digits, invent ISBN and VIN check digits, and guess a card's brand wrong. veridigit gives an agent a deterministic, authoritative answer instead: it runs the real checksum algorithms and returns structured results with the parsed parts and clear error reasons.

It ships as both an MCP server (for agents to call live) and a typed TypeScript library (for apps to import).

Supported in v1:

• IBAN — ISO 7064 mod-97 checksum + country-specific length, for 75+ countries.
• Payment cards — Luhn (ISO/IEC 7812) checksum, brand detection from the BIN

(Visa, Mastercard, Amex, Discover, Diners, JCB, UnionPay), and length rules.

• ISBN-13 — 978/979 prefix and mod-10 weighted check digit.
• VIN — ISO 3779 alphabet (no I/O/Q) and the position-9 transliteration check digit.

Why

On 32 randomly generated, non-memorised identifiers, a frontier model with no tool got the check digit wrong 91% of the time — IBAN 100%, VIN 100%, ISBN-13 88%, card/Luhn 75% — versus 0% for veridigit. The failure is invisible: the model returns a confident, well-formatted answer that happens to be wrong. veridigit replaces the guess with the algorithm.

Benchmark and reproducible harness: https://qinisolabs.github.io/veridigit

The 91% figure is one frontier model, tool-free, at temperature 0. Run it on any model yourself with the harness in bench/.

Use as an MCP server

// in your MCP client config
{
  "mcpServers": {
    "veridigit": { "command": "npx", "args": ["-y", "veridigit"] }
  }
}

Tools exposed: validate_iban, validate_card, validate_isbn, validate_vin.

Use as a library

npm install veridigit

import { validateIban, validateCard, validateIsbn13, validateVin } from "veridigit";

validateIban("GB82 WEST 1234 5698 7654 32");
// { valid: true, countryCode: "GB", country: "United Kingdom", checkDigits: "82", ... }

validateCard("4111 1111 1111 1111");
// { valid: true, luhnValid: true, brand: "Visa", lengthValid: true, ... }

validateIsbn13("978-0-306-40615-7"); // { valid: true, type: "ISBN-13", checkDigit: "7", ... }
validateVin("1HGCM82633A004352");    // { valid: true, checkDigit: "3", ... }

Helper exports are also available: ibanCheckDigits, luhnValid, luhnCheckDigit, detectBrand, isbn13CheckDigit, vinCheckDigit, supportedIbanCountries.

Scope

veridigit validates the structure of an identifier — its format and checksum. It does not confirm that a bank account, card, book or vehicle actually exists, is active, or belongs to anyone. It performs no network calls.

Development

npm install
npm run build   # tsc -> dist/
npm test        # parity/known-answer tests via tsx

The curated reference data (IBAN country specs, card BIN ranges) lives in data/.

License

Apache-2.0