Since I tried to played the game last time I had an issue, I have tons of .ydk decks but the game doesn't allow for more than one deck upload at a time.
With that issue in mind I made a script for Tampermonkey/Violentmonkey that allows users to import decks faster than manually.
You can download it here: https://greasyfork.org/pt-BR/scripts/501241-import-multiple-decks-to-duelingbook
And this is the script UI:
If this is in any way shape or form against the rules or need to be verified somehow please contact me.