Check-Digit Algorithms

pii_text detects credit-card and IBAN shapes by regex and data_quality does type / range / regex validation, but nothing actually computes or verifies a check digit. This adds the shared arithmetic engine for the four schemes behind most real-world identifiers — and the primitive that account-number, card, IBAN, ISBN and EAN validation build on.

Pure standard library (integer arithmetic; the Verhoeff and Damm tables are small embedded constants). Every function is pure (string in, bool / str out), so it is fully deterministic in CI.

Headless API

from je_auto_control import (
    luhn_validate, luhn_check_digit,
    verhoeff_validate, verhoeff_check_digit,
    damm_validate, damm_check_digit,
    mod97_10_validate, mod97_10_check_digits,
)

luhn_validate("4111111111111111")    # True  (credit-card / IMEI)
luhn_check_digit("7992739871")        # '3'   -> 79927398713
verhoeff_validate("2363")             # True  (catches transpositions)
damm_check_digit("572")               # '4'
mod97_10_validate("3214282912345698765432161182")   # True  (IBAN engine)

  • Luhn (mod 10): credit cards, IMEI, many national IDs — catches all single-digit errors and most adjacent transpositions.

  • Verhoeff and Damm: decimal schemes that catch all single-digit and adjacent-transposition errors (stronger than Luhn).

  • ISO 7064 MOD 97-10: the two-check-digit scheme behind IBAN and similar.

Each scheme exposes *_validate(number) (does the value incl. its check digit verify?) and *_check_digit / *_check_digits (what digit(s) to append to a bare payload?). Non-digit characters are ignored, so spaced/grouped input works.

Executor commands

AC_checksum_validate takes a scheme (luhn / verhoeff / damm / mod97) plus a number and returns {valid}; AC_checksum_digit returns {check_digit} for a partial. Both are exposed as MCP tools (ac_checksum_validate / ac_checksum_digit) and as Script Builder commands under Data.