Credit Card Validator
Check a card number with the Luhn algorithm and detect the card type — private and free.
Validate a card number's format
The Credit Card Validator checks whether a card number is structurally valid using the Luhn algorithm and identifies the card type — Visa, Mastercard, American Express, Discover, and more. It's a developer and testing tool that runs entirely in your browser; no number is ever sent anywhere.
What is the Luhn algorithm?
The Luhn algorithm (or "mod 10" check) is a simple checksum formula used to catch accidental errors in identification numbers, including credit cards. By doubling every second digit and summing the results, it verifies the number is internally consistent. Almost all card numbers must pass the Luhn check, so it instantly flags typos and invalid numbers — though it does not prove a card actually exists.
How to use it
- Enter a card number (spaces are fine).
- See instantly whether it passes the Luhn check.
- Read the detected card type and digit count.
How card types are detected
| Type | Starts with |
|---|---|
| Visa | 4 |
| Mastercard | 51–55, 2221–2720 |
| American Express | 34, 37 |
| Discover | 6011, 65 |
What this does and doesn't do
This validator confirms a number is well-formed — the right length and a valid checksum. It does not verify that the card is real, active, or has funds; only the issuing bank's payment network can do that. It's intended for developers testing payment forms, validating input formatting, and learning how the Luhn check works — not for assessing real cards.
An important safety note
Never enter a real credit card number you own into untrusted websites. This tool is safe because it runs entirely in your browser and transmits nothing, but as a general rule, only enter card details on secure, trusted payment pages. For testing, use the standard published test card numbers provided by payment processors.
Private and free
All checks run locally in your browser — nothing is uploaded or stored. The tool is completely free with no sign-up.
Frequently asked questions
Does this prove a card is real?
No. It only checks the number's format and checksum (Luhn). Only the card network can confirm a card is real and active.
What is the Luhn check?
A simple checksum that detects typos in card numbers by doubling alternate digits and verifying the total is divisible by 10.
Is it safe to enter a card number?
This tool transmits nothing — it runs in your browser. Still, only enter real cards on trusted payment pages; use test numbers here.
Is it free?
Yes, completely free with no sign-up, running entirely in your browser.