- Scryfall: The best Magic card database out there. Learn the advanced functions, they’ll save you so much time.
- Comprehensive Rules: Invaluable for those awkward rules interactions. Also a linkable version on magiccards.info here.
- MTG Salvation Wiki: Excellent wiki on all aspects of the game.
- Marmaris74’s Art Dump: Over a thousand hand-picked fantasy pictures for your cards.
- Websites for Art: A few dozen websites for appropriate art collected in one place!
- The Custom Magic Mechanic Database: 100+ custom mechanics from all across the internet. Hugely helpful for inspiration.
- Concise List of Cards Every Set Could Include: A list of staples to help fill the holes in your set.
- Cockatrice Export Script: A helpful method and guide to exporting your custom sets for use in Cockatrice.
- As-Fan Calculator: Powerful calculator for determining the frequency of any given aspect of your set in the average booster.