damm32

Base32 check digits using the Damm algorithm, which detects every single-character error and every adjacent transposition. Useful for human-entered codes such as licence keys, voucher codes and sample IDs.

The alphabet leaves out easily confused characters (0/o, 1/i/l):

23456789abcdefghjkmnpqrstuvwxyz*

Input is case-insensitive. No dependencies; works in Node.js 20+ and modern browsers. TypeScript declarations are included.

Install

npm install damm32

Usage

import { checkDigit, isValid, value, INVALID } from 'damm32';

checkDigit('fdfsdfds');  // '3', or INVALID ('-') if a character is outside the alphabet
isValid('fdfsdfds3');    // true
isValid('fdfsdfd3s');    // false (transposition detected)
value('f');              // 0-31, or -1 if not in the alphabet

Command line

npx damm32 -a fdfsdfds        # fdfsdfds3
npx damm32 -c fdfsdfds3       # exit status 0 if valid, 1 if not

Run npx damm32 --help for all options. Quote codes containing * in the shell.

C and PHP implementations with identical output are in the GitHub repository.

Licence

BSD 2-Clause