Deck Registration Sheet
Paste a decklist or a deck URL and download the official Wizards registration form with your deck filled in. Pasted lists recognise a Sideboard header — also SIDEBOARD: and // Sideboard (15) — and everything before it is the main deck.
mtgtop8 and Archidekt work. For mtgtop8, use a link to the deck itself — one with &d=. Moxfield refuses requests from any server, so its links can't work here: in Moxfield use More → Export and paste the list instead.