Just the first 11 digits of the card number. They include the BIN (Bank Identification Number) and identify the issuer and card product, which is what determines the interchange rate. You never need to enter a full card number.

Standard commercial credit carries the highest interchange — often 2.5–3%+ — and that cost comes straight out of your margin. But that standard rate isn't fixed: many commercial cards fall into variable interchange programs, where a lower rate can be negotiated with the card network or the issuing bank — or avoided by steering the buyer to a lower-cost card. And at the low end, regulated commercial debit can settle for as little as 0.05%. Knowing which program a card falls into before you accept it is what gives you the leverage to capture that difference.

Yes. The tool only uses the first 11 digits, which aren't a usable card number. If you paste a full card number, it's cut to the first 11 digits in your browser before anything is sent, so the rest is never transmitted or stored.