this post was submitted on 21 Oct 2025
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MTG Deck Legality Checker for custom formats! (git.disroot.org)
submitted 2 months ago* (last edited 1 month ago) by counterspell@mtgzone.com to c/mtg@mtgzone.com
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Hey everyone!

I just finished building a web tool to help validate Magic: The Gathering decklists in any custom format. It fetches card data from Scryfall, checks for banned or illegal cards, and gives instant feedback right in your browser.

It’s perfect for experimenting with niche formats, casual play, or even building decks for some existing formats like Standard Penny Dreadful, 2015 Modern, Classic Legacy, Pre Fire Modern, Pre Horizons Modern, Pre Modern. It can also integrate with Moxfield for deck building.

Check it out here: https://git.disroot.org/hirrolot19/mtg-legality-checker

I’d love to hear your thoughts, suggestions, or ideas for improving it. Hope it helps deckbuilders and casual players alike!

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[–] counterspell@mtgzone.com 1 points 1 month ago* (last edited 1 month ago)

This tool isn’t really needed given that there are multiple websites, where you can upload your collection and your deck, and they will tell you exactly which cards in the deck are missing from your collection.

For example:

  • Archidekt — collection tracker + deck builder
  • Moxfield — modern deck builder with collection support
  • Deckstats — deck-building + collection management
  • Deckbox — collection manager that shows missing cards for a deck
  • ManaBox — app for collection tracking + deck building
  • MTGGoldfish — has features to input your collection and compare against decks
  • Untapped.gg — for MTG Arena, tells you which decks you can build given your collection

So while a custom format legality checker is neat, if your goal is simply “which cards do I lack in this deck given my collection”, one of those sites will do just fine.