runs entirely in your browser — your sensitive data is never sent to our server,…') Credit Card Validator (Luhn) — Free Security Tool | ToolSelf Skip to main content

Luhn Validator

The Luhn Algorithm Validator checks whether a credit card number, IMEI, or other identifier passes the Luhn checksum — the mathematical formula used to detect typos and data entry errors. Enter any number to instantly verify if it has a valid Luhn check digit, useful for validating card numbers in development and testing without making real API calls.

Share this tool
Developer Tools

About the Luhn Algorithm Validator

The Luhn Algorithm Validator checks whether a credit card number, IMEI, or other identifier passes the Luhn checksum — the mathematical formula used to detect typos and data entry errors. Enter any number to instantly verify if it has a valid Luhn check digit, useful for validating card numbers in development and testing without making real API calls.

How to use it

  1. Enter the number you want to validate (credit card, IMEI, etc.).
  2. Click Validate to run the Luhn algorithm check.
  3. See if the number is valid or invalid with the step-by-step calculation.
  4. Use the generator to create valid test numbers for development.

Formula & methodology

Starting from the rightmost digit (check digit), moving left: double every second digit. If doubled value > 9, subtract 9. Sum all digits. If total mod 10 = 0, number is valid. Check digit generation: calculate sum of all digits except last, check digit = (10 - (sum mod 10)) mod 10.

Common use cases

  • Validating credit card number format before API submission
  • Generating valid test card numbers for payment integration testing
  • Verifying IMEI numbers for device validation
  • Implementing client-side card number validation in checkout forms
  • Detecting typos in manually entered card or account numbers

Frequently asked questions

No — Luhn validation only checks that the number has a valid checksum format. It does not verify the card exists, is active, has funds, or belongs to a real account. A number can pass Luhn validation and be completely fictional. To verify a real card, you must use a payment processor API. Luhn is purely a checksum to catch typos, not a security measure.
Payment processors provide official test card numbers. Visa test: 4111111111111111. Mastercard test: 5500005555555559. Amex test: 378282246310005. These all pass Luhn validation and are recognized by sandbox environments. Never use real card numbers in development or testing — always use the processor's official test credentials.

Related tools

All Tools →
Security

Password Generator
Security

Password Crack Time Estimator
Security

Password Strength Checker
Security

SHA Hash Generator
Security

MD5 Hash Generator

Embed this tool on your site

Free for personal and commercial use. Just copy the snippet below.