card-precheck

card-precheck is a lightweight JavaScript utility for validating credit and debit card numbers before sending them to a payment gateway.

It helps developers catch obviously invalid card input early by applying public industry rules such as checksum validation and card brand patterns. This improves user experience and reduces unnecessary payment API requests.

This package is designed for pre-validation only and is not a replacement for payment processor authorization.

Installation

npm install card-precheck

Basic usage

const { validateCardNumber } = require("card-precheck");

const result = validateCardNumber("4242 4242 4242 4242");

console.log(result);
/*
{
  isValid: true,
  cardType: "visa",
  reason: null
}
*/

What it does

• Validates card numbers using the Luhn algorithm
• Identifies card brands based on known prefixes and lengths
• Rejects malformed or impossible card numbers
• Works offline with no network calls
• Can be used client-side or server-side

What it does not do

card-precheck does not:

• Verify that a card exists
• Check available funds
• Perform authorization or charges
• Validate CVV or expiry dates
• Detect stolen, blocked, or fraudulent cards

A card that passes validation may still fail when processed by a payment provider. Final verification must always be handled by a PCI-compliant gateway such as Stripe, Paystack, Adyen, or similar services.

Why this exists

When building SaaS products with free trials or delayed billing, developers often want to:

• Prevent obviously fake card numbers during signup
• Improve form validation and error feedback
• Reduce spam or bot-generated inputs
• Avoid unnecessary calls to payment APIs

card-precheck provides a fast, local way to validate card input before involving a payment processor.

Common use cases

• Disable form submission until a card number is valid
• Validate card input during onboarding or trial signup
• Improve UX with immediate feedback
• Reduce invalid payment attempts

Security and compliance notes

• This library does not store, transmit, or log card numbers
• Avoid logging raw card data in your application
• Do not rely on this package for fraud prevention
• Always use a PCI-compliant payment provider for real transactions

Supported card types

• Visa
• Mastercard
• American Express
• Discover

Philosophy

Credit card validation rules are public knowledge. card-precheck applies these rules clearly and responsibly, without implying bank-level verification or authorization.

Disclaimer

This package performs format and checksum validation only. It provides no guarantees regarding card authenticity, authorization success, or fraud prevention.

License

• MIT