How to Build a BIN Lookup Middleware in Node.js in Under an Hour

TL;DR A BIN (Bank Identification Number) is the first 6 to 8 digits of any payment card and tells you the issuing bank, card type, country of origin, and whether the card is prepaid or credit. You will build a reusable Express middleware function that intercepts incoming card data, calls a BIN lookup API, and attaches structured metadata to req.binInfo . The final middleware lets you block prepaid cards, filter by country, flag high-risk issuers, and add card branding in one clean layer before your payment logic runs. Stack: Node.js 18+, Express 4, Axios, dotenv. Total build time: under 60 minutes if you follow every step. Why BIN Lookup Middleware Is Worth Your Time If you process payments, subscriptions, or any kind of card-based transaction, you already know that not all cards are created equal. A prepaid card from a high-risk country behaves very differently from a corporate Visa issued by a US bank. Your fraud rules should know the difference before a charge attempt ever reaches S