Question 1

What is the Luhn algorithm and what does this validator do?

Accepted Answer

The Luhn (mod-10) algorithm is a simple checksum formula used to validate identification numbers like credit cards, IMEI codes, gift cards, and Canadian SINs. This tool computes the checksum locally in your browser, tells you pass/fail, shows the corrected check digit when validation fails, displays the step-by-step doubling visualization, and detects the card brand from the BIN/IIN prefix.

Question 2

Which card brands can this tool detect?

Accepted Answer

Visa, Mastercard (including the 2-series 2221-2720 range), American Express, Discover, JCB, Diners Club, UnionPay, and Maestro. Each brand has known BIN/IIN prefixes and allowed lengths — the matcher prefers the longest prefix so 622126-622925 correctly resolves to Discover rather than UnionPay, and 3528-3589 resolves to JCB.

Question 3

Can I validate IMEI, gift card, or other non-card numbers?

Accepted Answer

Yes. Choose a mode: Credit Card (12-19 digits), IMEI (14 digits + check digit = 15), Gift Card (configurable 12-19 digits), or Any (no length constraint). The Luhn algorithm itself is mode-agnostic; modes only constrain accepted length and turn off brand detection for non-card inputs.

Question 4

Does this tool store or transmit my card numbers?

Accepted Answer

Never. Every computation runs 100% client-side in JavaScript. There is no server endpoint, no analytics on the input field, and no console logging of card data. The history feature (last 20 operations) stores only a count and timestamp in localStorage on this device — never the card numbers themselves.

Question 5

What extra features does this tool have versus other Luhn validators?

Accepted Answer

(1) Single-number live validation with pass/fail. (2) Eight-brand BIN detection. (3) Step-by-step doubling visualization. (4) Corrected check-digit suggestion on failure. (5) Adjacent-transposition hint (catches the most common typing error). (6) Four display formats (plain, spaced, dashed, grouped 4-6-5 for Amex). (7) Masked display toggle. (8) Four input modes (credit, IMEI, gift, any). (9) Bulk paste with per-line valid/invalid table. (10) CSV export of bulk results. (11) Wikipedia + Stripe canonical test vectors. (12) localStorage history (max 20, no numbers stored). (13) Shareable URL with mode + format encoded in fragment.

Luhn / Credit Card Validator

Single-number validation

Batch validation

Reference

How to use

Single-number validation

Batch validation

Reference