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Credit card luhn validator

Runs the Luhn check on a card number with every doubling step shown, detects the brand, and handles a batch list.
Card number, one per line for a batchPartial digitsEverything before the check digit

Enter a card number to check it.

A Luhn pass says the digits are self consistent and nothing more. It does not say the card is real, active, or open with any institution, and a matching brand pattern is a guess from public prefix ranges, not a BIN database. The working below doubles every second digit from the right, folds two digit products by subtracting nine, and passes when the total ends in 0; the check digit field runs the same arithmetic backwards to complete a partial number. Batch output shows masked numbers only, because pasted lists can carry real card numbers. These are format checks on numbers you paste, all computed in this tab.
Options

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