BrowserTools

Luhn Algorithm Validator

Validate & generate Mod 10 checksum numbers

By Guga — BrowserTools maintainer, Tbilisi, Georgia Updated 2026-09-03
Free Private No uploads
What is Luhn Algorithm Validator?

Two tabs cover both halves of the job. The Verify tab strips every non-digit out of what you type, doubles alternate digits from the right, and reports the running sum, the remainder after dividing by 10, the digit count and the last character, so a failure tells you how far off the arithmetic landed rather than just that it failed. The Generate tab fills the body of a number with random digits and appends the correct check digit, which means every sequence it produces passes validation by construction. Sequence Length offers 12, 14, 15, 16 (marked standard) and 19 digits, and the optional Custom Prefix pins the leading digits — useful for asserting a 4 prefix or a 51 prefix in a suite. Count goes from 1 to 50 per run.

Validate numeric sequences using the Luhn algorithm (Mod 10 formula) and generate sample checksum-compliant sequences for software development, form validation, and QA testing.

Private Luhn Algorithm Validator In Your Browser

Luhn Algorithm Validator is processed locally with client-side JavaScript. Your files never touch a server, and there is no queue to wait in.

Step-by-Step

How to use Luhn Algorithm Validator

1

Open Verify Luhn Checksum, paste digits into the sequence field, and watch the digits, Luhn sum, remainder and last digit panels update as you type.

2

Switch to Generate Test Sequences when you need fixtures rather than a verdict.

3

Choose a Sequence Length of 12, 14, 15, 16 or 19 digits and a Count from 1 to 50.

4

Type up to six digits into Custom Prefix if the leading characters matter, then press Generate Luhn Numbers.

Key Capabilities
  • Verify mode shows the digit count, the doubled-digit sum, the sum modulo 10 and the final character alongside the verdict.
  • Generate mode appends a mathematically correct check digit rather than picking digits at random and hoping.
  • Sequence length presets of 12, 14, 15, 16 and 19 digits, with 16 labelled standard.
  • Custom Prefix accepts up to six digits and is applied before the random body is filled in.
Common Use Cases
  • A payments developer reproducing a card-validation bug pastes the number a customer typed in and reads the remainder to confirm the mismatch.
  • A QA engineer writes a unit test for a Mod 10 input mask and needs 20 valid IMEI-shaped fixtures with a 4 prefix.
  • A student checks whether the check digit on their student ID follows the formula before trusting it in a form submission.
Clear Answers

Frequently Asked Questions

A number passed the check. Does that mean it exists?
No. The Luhn formula detects transcription errors, nothing more. Roughly one number in ten passes, so a pass tells you the digits are probably not mistyped; it says nothing about whether an account, card or device exists.
What happens to letters and spaces I paste in?
They are removed before the calculation, so 4532 0115 0323 6472 is evaluated as digits only. That also means a string of nothing but letters clears to empty and is treated as no input rather than as a zero.
My custom prefix makes the number longer than the chosen length. Is that a bug?
It is a consequence of how the body is filled. The generator appends random digits only while the string is shorter than length minus one, then appends the check digit, so a prefix at or past that threshold produces a shorter number than the preset rather than an error.