uk-modulus-check

UKModulusCheck

Overview

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

It only users vanilla typescript, and can be used on the frontend.

Vocalink periodically 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 {validateAccountDetails} from "uk-modulus-check";


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

const {validateAccountDetails} = require("uk-modulus-check");

console.log(validateAccountDetails('180002', '00000190')); // true
console.log(validateAccountDetails('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), any combination of sort-code and account number will be considered valid. This is because the Vocalink data doesn't seem to have 100% coverage.

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 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), and I'm not sure it can be used directly in the frontend given 'fs' dependency, which motivates the creation of this package.