uk-modulus-check

UKModulusCheck

Overview

TypeScript class that validates UK bank account details using the modulus checking algorithm.

It only users vanilla typescript, and the 'fs' file-loading library.

From time to time, Vocalink updates the txt files here mapping sort-code ranges to validation weights. We currently use v7-90 (valid from 17 August 2024).

Status

Installation

npm install uk-modulus-check

See here for the NPM package.

Usage

import ModulusChecker from "uk-modulus-check";

const checker = new ModulusChecker();

console.log(checker.validate('180002', '00000190')); // true
console.log(checker.validate('938063', '15763217')); // false

Details

This specification details logic to differentiate valid vs. invalid pairs of sort-code and account number.

A mathematical algorithm compares the two values, and check if the two can be paired together legitimately.

This page details any changes to the specification.

Technicalities

In general, I tried to minimise risk of returning false for a valid bank account.

1. if an account has an unseen sort code (not covered by any range in src/data/valacdos), by default, any combination of sort-code and account number will be considered valid. This is altered by instantiating a check with ModulusChecker(false) and then default behaviour will be set to false

2. I find the specification a bit confusing for some examples, specifically when 2 checks are run on the same account. I mark the account as valid if either of the two validations pass, for cases where multiple validations are provided for the same account. The specific test-cases in listest examples are 23, 27, 28.

Both (1) and (2) might lead to a small % of 'false positives'.

License

MIT

Credits

Thanks to uphold/uk-modulus-checking for creating a good Javascript implementation.

It doesn't seem to have been updated since valacdos-v640 (12/10/2020), which motivates the creation of this package.