finprim

Financial primitives for modern TypeScript applications.

IBAN · BIC/SWIFT · Card · Sort Code · VAT · Routing Number · Loan/EMI · Currency
One library. Zero dependencies. Fully typed.

Every fintech team builds this internally. Sort code validation here, an IBAN check there, a custom currency formatter somewhere else. It's fragmented, inconsistent, and expensive to maintain. finprim is the open source version of what your team has already written three times.

Quick Start

npm install finprim

import { validateIBAN, validateCardNumber, formatCurrency } from 'finprim'

const iban = validateIBAN('GB29NWBK60161331926819')
// { valid: true, value: 'GB29NWBK60161331926819', formatted: 'GB29 NWBK 6016 1331 9268 19', countryCode: 'GB' }

const card = validateCardNumber('4532015112830366')
// { valid: true, formatted: '4532 0151 1283 0366', network: 'Visa', last4: '0366' }

formatCurrency(1000.5, 'GBP', 'en-GB')
// '£1,000.50'

That's it. No config. No setup. Just import and use.

Why finprim?

Problem	finprim
5 different npm packages for financial validation	One unified library
Custom glue code between validators	Consistent API across all validators
Runtime type confusion	Branded TypeScript types for compile-time safety
No framework integration	Built-in Zod schemas, React hooks, NestJS pipes
Heavy dependency trees	Zero runtime dependencies

Features

Validators - IBAN (80+ countries), BIC/SWIFT, UK sort code & account number, card number (Luhn + network detection), EU VAT, US ABA routing number
Loan math - EMI calculation and full amortization schedules
Formatting - Display-ready IBAN, sort code, account number, and multi-locale currency formatting
Branded types - Compile-time correctness that prevents invalid data from flowing through your system
Framework integrations - Zod schemas, React hooks, NestJS pipes (all optional)
Production-ready - Input length guards, type checking, no sensitive data logging
Lightweight - Zero dependencies, tree-shakeable ESM + CJS

Integrations

finprim works standalone or plugs into your existing stack:

Import path	What it contains	Extra dependency
`finprim`	Core validators, formatters, loan math	none
`finprim/zod`	Zod schemas for validation pipelines	`zod`
`finprim/react`	React hooks for form inputs	`react`
`finprim/nest`	NestJS validation pipes	`@nestjs/common`

Usage Examples

Validation

import {
  validateIBAN,
  validateUKSortCode,
  validateUKAccountNumber,
  validateBIC,
  validateCardNumber,
  validateCurrencyCode,
  validateEUVAT,
  validateUSRoutingNumber,
} from 'finprim'

validateIBAN('GB29NWBK60161331926819')
// { valid: true, value: 'GB29NWBK60161331926819', formatted: 'GB29 NWBK 6016 1331 9268 19', countryCode: 'GB' }

validateUKSortCode('60-16-13')
// { valid: true, value: '601613', formatted: '60-16-13' }

validateUKAccountNumber('31926819')
// { valid: true, value: '31926819', formatted: '3192 6819' }

validateCardNumber('4532015112830366')
// { valid: true, formatted: '4532 0151 1283 0366', network: 'Visa', last4: '0366' }

validateEUVAT('DE123456789')
// { valid: true, value: 'DE123456789', formatted: 'DE 123456789', countryCode: 'DE' }

validateUSRoutingNumber('021000021')
// { valid: true, value: '021000021', formatted: '021000021' }

Formatting & Display

import { formatIBAN, formatSortCode, formatUKAccountNumber, formatCurrency, parseMoney } from 'finprim'

formatIBAN('GB29NWBK60161331926819')        // 'GB29 NWBK 6016 1331 9268 19'
formatSortCode('601613')                     // '60-16-13'
formatUKAccountNumber('31926819')            // '3192 6819'

formatCurrency(1000.5, 'GBP', 'en-GB')      // '£1,000.50'
formatCurrency(1000.5, 'EUR', 'de-DE')       // '1.000,50 €'
formatCurrency(1000.5, 'USD', 'en-US')       // '$1,000.50'

parseMoney('£1,000.50')
// { valid: true, amount: 1000.50, currency: 'GBP', formatted: '£1,000.50' }

Loan / EMI Calculation

import { calculateEMI, getLoanSchedule } from 'finprim'

calculateEMI(100_000, 10, 12)
// Monthly payment amount

getLoanSchedule(100_000, 10, 12)
// [{ month, payment, principal, interest, balance }, ...]

Branded Types

import type { IBAN, SortCode, AccountNumber } from 'finprim'

// Invalid data cannot be passed where valid data is expected
function processPayment(iban: IBAN, amount: number) { /* ... */ }

const result = validateIBAN(input)
if (result.valid) {
  processPayment(result.value, 100) // result.value is typed as IBAN
}

Zod Schemas

import { z } from 'zod'
import { ibanSchema, sortCodeSchema, accountNumberSchema, currencySchema } from 'finprim/zod'

const PaymentSchema = z.object({
  iban: ibanSchema,
  sortCode: sortCodeSchema,
  accountNumber: accountNumberSchema,
  amount: z.number().positive(),
  currency: currencySchema,
})

React Hooks

import { useIBANInput, useCardNumberInput, useCurrencyInput } from 'finprim/react'

function PaymentForm() {
  const iban = useIBANInput()
  const card = useCardNumberInput()
  const currency = useCurrencyInput('GBP', 'en-GB')

  return (
    <form>
      <input value={iban.value} onChange={iban.onChange} aria-invalid={iban.valid === false} />
      <input value={card.formatted} onChange={card.onChange} aria-invalid={card.valid === false} />
      <input value={currency.formatted} onChange={currency.onChange} />
    </form>
  )
}

NestJS Pipes

import { IbanValidationPipe, SortCodeValidationPipe, createValidationPipe } from 'finprim/nest'
import { validateIBAN } from 'finprim'

@Get('iban/:iban')
findByIban(@Param('iban', IbanValidationPipe) iban: string) {
  return this.service.findByIban(iban)
}

// Create a custom pipe from any validator
const MyPipe = createValidationPipe(validateIBAN)

API Reference

Validation

Function	Input	Returns
`validateIBAN(input)`	`string`	`IBANValidationResult` (includes `countryCode`)
`validateUKSortCode(input)`	`string`	`ValidationResult<SortCode>`
`validateUKAccountNumber(input)`	`string`	`ValidationResult<AccountNumber>`
`validateCurrencyCode(input)`	`string`	`ValidationResult<CurrencyCode>`
`validateBIC(input)`	`string`	`ValidationResult<BIC>`
`validateCardNumber(input)`	`string`	`CardValidationResult` (includes `network`, `last4`)
`validateEUVAT(input)`	`string`	`VATValidationResult` (includes `countryCode`)
`validateUSRoutingNumber(input)`	`string`	`ValidationResult<RoutingNumber>`

Formatting

Function	Input	Returns
`formatIBAN(input)`	`string`	`string` (space-separated)
`formatSortCode(input)`	`string`	`string` (XX-XX-XX)
`formatUKAccountNumber(input)`	`string`	`string` (XXXX XXXX)
`formatCurrency(amount, currency, locale?)`	`number`, `SupportedCurrency`, `string?`	`string`
`parseMoney(input)`	`string`	`MoneyResult`

Loan

Function	Input	Returns
`calculateEMI(principal, rate, months)`	`number`, `number`, `number`	`number`
`getLoanSchedule(principal, rate, months)`	`number`, `number`, `number`	`LoanScheduleEntry[]`

Roadmap

IBAN validation (80+ countries)
BIC/SWIFT validation
Card number validation (Luhn + network detection)
EU VAT number validation
US routing number validation
UK sort code and account number validation
Loan/EMI calculation
Format-only helpers
Currency formatting with locale support
Branded TypeScript types
Zod schema integration
React hooks
NestJS pipes
More locale coverage
SEPA credit transfer XML generation
ACH file format support

Security

Input length - All string validators reject input longer than 256 characters
Type checking - Validators require non-empty strings; numeric helpers require finite numbers and sane bounds
No sensitive logging - The library does not log or persist input
Format helpers - Cap input length and accept only strings

Contributing

Contributions are welcome! Please see CONTRIBUTING.md for guidelines.

git clone https://github.com/tintolee/finprim.git
cd finprim
npm install
npm test

License

MIT