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Clear, accurate guides on BINs, card networks, the Luhn algorithm and safe payment testing — written for developers and the curious alike.

BINIIN

What Is a BIN (Bank Identification Number)?

The leading digits of any payment card encode its network, issuer, and card type — but never the account or cardholder. Here's what a BIN is, what it reveals, and what it can't.

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luhncard-validation

How the Luhn Algorithm Validates Card Numbers

The Luhn algorithm is the mod-10 checksum that catches mistyped card numbers before checkout. Here's how it works, worked by hand, with its real limits.

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test cardspayments

Test Card Numbers: How to Test Payments Safely

Why 4111 1111 1111 1111 works, the difference between PSP and generated test numbers, and how test cards pass Luhn yet can never be charged — plus safe QA practices that keep real cards out of your tests.

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PANBIN

Anatomy of a Card Number: BIN, Account Number & Check Digit

Every digit on a card has a job. Here's how the MII, BIN, account number, and Luhn check digit fit together — and why lengths and grouping differ per network.

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GlossaryPlain-English definitions of BIN, IIN, PAN, Luhn and more.ExploreFAQAnswers about BIN lookups, validation, privacy and how the tools work.ExploreAll toolsSix free, private card utilities — try them right now.Explore