If you're here, you too have enjoyed the lovely months-long inability to import transactions from your Discover card into YNAB. I wrote this tool to help ease the pain.
If you're just looking for a tool you can use without any setup, I have a hosted version of this tool at https://projects.opilo.net/ynab/.
You'll need a server running PHP; I'd recommend at least version 7. The functions it uses are included by default, but certain distributions may require you to install the php-xml package.
This tool and the code that powers it are a gift to the YNAB userbase. If you're YNABing correctly, your money has more important jobs than giving it to me. Instead, call Discover customer support at 1-800-347-2683 or chat with them at https://www.discover.com/credit-cards/contact-us/ and tell them if they don't restore native OFX exports in the next 3 months, you're cancelling your card. Seriously. If enough of us do it, they'll either listen or lose customers.