Luhn Algorithm Checker — Validate & Generate Credit Card Numbers

Overview

Luhn Algorithm Checker validates and generates numbers using the Luhn (mod 10) checksum.

🔗 https://devnestio.pages.dev/luhn-checker/

What it validates

Credit cards (Visa, Mastercard, Amex, Discover), IMEI codes, ISIN identifiers, and more.

The algorithm

1. From the rightmost digit, double every second digit
2. If doubling > 9, subtract 9
3. Sum all digits — if sum mod 10 = 0, valid

function luhn(digits) {
  let sum = 0;
  for (let i = 0; i < digits.length; i++) {
    let d = digits[i];
    if (i % 2 === 1) { d *= 2; if (d > 9) d -= 9; }
    sum += d;
  }
  return sum;
}

Features

• Instant valid/invalid banner with color coding
• Step-by-step digit breakdown table
• Generate mode: enter prefix → get correct check digit
• Card type detection (Visa, Mastercard, Amex, Discover, JCB, Diners)

👉 Try it: https://devnestio.pages.dev/luhn-checker/