Posts on X2Q tagged mastercard. Updated as new posts are published.
A practical reference for BIN/IIN lookups: what the issuer identification number is, the table of which prefix ranges belong to which card network, and the three ways to look a BIN up — read it off the ranges yourself, use a lookup site/API like binlist.net, or query it programmatically. Includes the 6-vs-8-digit caveat and what you can and can't tell from a prefix alone.
The card networks expanded the issuer identifier on a payment card from 6 to 8 digits. For anyone doing BIN/IIN lookups it means a 6-digit prefix is no longer guaranteed to identify a single issuer — you often need 8 digits to disambiguate. Here's the what, the why, and the practical fallout.
In 2013, sitting on a balcony in Playitas, Fuerteventura, I built binlist.net as my first ever Go project — a free HTTP API for looking up the issuer of a credit card from its first six digits. It hit 1 million queries/day by 2015. Thirteen years later it's still free, and its commercial sibling iinlist.com is the one we run the business on.