Luhn Algorithm Tool
The Luhn Algorithm Tool lets you validate whether any number passes the Luhn (mod 10) checksum used by credit cards, IMEI numbers, and other identification systems. Use it to validate test card numbers during payment form development, compute the correct check digit for a partial number, or learn step-by-step how the Luhn algorithm works. Also displays official published test numbers from Visa, Mastercard, American Express, and Discover. All computation happens locally in your browser.
Luhn Algorithm Tool
Validate card numbers using the Luhn algorithm and compute check digits — for development and education.
Educational & Developer Tool
This tool demonstrates the Luhn algorithm used to validate credit card, IMEI, and other identification numbers. For official payment testing, use your payment processor's documented test numbers (e.g., Stripe, PayPal, or Braintree test credentials).
Official Test Numbers (from card networks)
Visa (official test)
4111111111111111
Mastercard (official test)
5500005555555559
Amex (official test)
371449635398431
Discover (official test)
6011111111111117
How to Use Luhn Algorithm Tool
- 1Choose a tab: Validate Number, Compute Check Digit, or How It Works
- 2To validate: enter any number and click Check Luhn Validity
- 3To compute: enter all digits except the last and click Compute Check Digit
- 4Use the official test numbers section to copy published test card numbers for payment sandbox testing
About Luhn Algorithm Tool
The Luhn Algorithm Tool lets you validate whether any number passes the Luhn (mod 10) checksum used by credit cards, IMEI numbers, and other identification systems. Use it to validate test card numbers during payment form development, compute the correct check digit for a partial number, or learn step-by-step how the Luhn algorithm works. Also displays official published test numbers from Visa, Mastercard, American Express, and Discover. All computation happens locally in your browser.
Your Privacy is Protected
Luhn Algorithm Tool runs entirely in your browser. Your files and data are never uploaded to any server, never stored, and never shared. Everything happens locally on your device using secure browser APIs.
Frequently Asked Questions
What is the Luhn algorithm?
The Luhn algorithm (mod 10) is a checksum formula used to validate identification numbers like credit cards, IMEI codes, and National Provider Identifiers. It catches most accidental digit errors.
Does passing the Luhn check mean a card is real?
No. The Luhn check only verifies the mathematical structure of the number. A number can pass the Luhn algorithm without being linked to any real account.
Where do the official test numbers come from?
The test numbers shown are the publicly documented test numbers published by Visa, Mastercard, Amex, and Discover themselves for developer sandbox testing.
What is this tool used for?
Developers use it to validate payment form input, generate correctly structured dummy data for UI testing, and learn how the Luhn algorithm works.
Why Use This Tool?
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