A ChatGPT Deckbuilder for Magic The Gathering: Arena

OpenAI began the rollout of CustomGPTs in Nov of 2023, and will be launching the GPT store sometime in 2024. In honor of the rollout, I figured I would dip back into creating custom GPTs, and decided to try my hand at a custom GPT focused on building and improving decks for the game Magic The Gathering: Arena.

It’s entitled MTG Arena Deckmaster, and you can grab the GPT here. In this article, I’ll explain how the GPT works and how it was built.

A ChatGPT Deckbuilder for Magic The Gathering: Arena

This GPT is designed primarily for two purposes:

  • To improve existing MTG Arena decks
  • To create novel, new decks

ChatGPT is not a world-class expert at strategy games like Stockfish is for chess playing. It can play basic games like chess, but it’s not able to wreck humans the way some of the chess and go engines can.

But what it is good at is organizing and understanding information. It basically has the entire scryfall database in its training, and understandings much of the strategy behind building MTG decks. It does a great job analyzing decks and recommending cards, and can also build decks based on your parameters.

Let’s look at each of the primary functions, and how they work.

Improving An Existing MTG Arena Deck

To amp up one of your existing decks, launch the GPT and click the “I would like to improve an existing MTG Arena deck” option. It will ask you a few questions about your deck, and then tell you to go to Arena, select your deck, and export it to your clipboard, then paste it into ChatGPT.

From there, it will analyze your deck and make recommendations for cards to remove, cards to add, strategies to change, etc.

For example, here is a deck that I had built focused around All Will Be One that was working well, but wasn’t quite synergizing the way I wanted. ChatGPT recommended a few changes and directions that I had not considered, leading me to make other changes later to further improve the deck.

When you’ve got the card list you want, ChatGPT can provide you with a card list that you can re-import into Arena and create a new copy of the deck.

Creating a New Deck From Scratch

The second primary function of this custom GPT is to create entirely new decks. To do this, click “I would like to create a new MTG Arena deck” and it will ask you some questions. These will likely include:

  • The type of deck you want to build (e.g. alchemy, explorer, brawl, etc.)
  • If there is a particular strategy or color combination you want to target
  • A card or combo you want to build the deck around, a style of deck (e.g. control, aggro, etc.)

Once the GPT has an idea what you’re looking to build, it will give you a card list. You’ll have to cross-reference the list with what you have available, and build your new deck.

In my example, I asked it to build a deck around the card Elusive Otter, which I happened to have 4 of in my library.

The deck it created is fun and entirely different than anything I would normally build. It’s not exactly super competitive, but on the other hand, Elusive Otter is not typically a card people are building entire decks around.

Here’s the deck we ended up with:

The Frustration With Arena’s Card Library

Unfortunately, you cannot currently export your entire card collection from Arena. If you could, that would make the deck editing and generation process much easier. Often, ChatGPT will make a suggestion to add 4 rares or mythics to your deck, but you don’t actually have them in your collection.

You can make them of course, but that gets costly over time!

So often there is some back and forth around “I don’t have Bonecrusher Giant in my collection, what is a suitable replacement?”

When you’re using this tool, you’ll likely be burning through lots of uncommons, rares, and mythics, so be prepared!

Hopefully WoTC will allow export again in the future.

Building the Custom GPT

Building a custom GPT like this is fairly easy.

You essentially chat with ChatGPT and explain what you’re looking for, and it builds the custom GPT for you. There are two windows: the right window is a version of the custom GPT, and the left window is the editor that allows you to provide the instructions and configurations to the GPT.

For example, I wanted to be sure that it reviewed the current card ban list before it recommended decks, so I included that in the instructions.

You can simply talk with ChatGPT and it will build everything out for you. Very cool!

Final Thoughts

When the ChatGPT Store launches, I suspect custom GPTs will be everywhere. However, most of them will likely be free, as they are certainly not as difficult to build as, say, iOS apps. At least, basic apps like the one above will be free.

If you’re a MTG Arena player, please give the custom GPT a try, and hopefully you’ll get some new ideas for decks!

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