Why ChatGPT makes up cards when you ask for a deck (and how to avoid it)

You ask ChatGPT for a Pokémon or Magic deck and get a list that sounds right: believable names, a clear plan, sixty cards. Then you look it up and one card does not exist, another rotated a year ago and a third has five copies. It is not bad luck: it is how a general chatbot works.

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A general chatbot versus an AI with a catalog

Reviewed on November 1, 2026

What each one does when you ask it for a deck. “Not confirmed” means its official site does not say so.

Tool	What it does best	Games	AI	Format legality	Card prices	Price	Platforms
ChatGPT	Talking through strategy for any game	Any (general chatbot)	Writes the list; OpenAI warns it can make things up	Not confirmed	Not confirmed	Free; paid from €8.00/month	Web, Android, iPhone
TCGJoin Deck Coach	Builds the whole deck from catalog cards, checks legality on the server and gives its cost in euros	Pokémon, Magic, One Piece, Lorcana +6 games	Builds the whole deck	Yes: official list for Pokémon, Magic, Yu-Gi-Oh! and Lorcana	EUR (Cardmarket · TCGplayer)	Free; paid from €3.99/month	Web, Android
Farseek	Commander AI that reads your 99 and suggests changes on a budget, searching Scryfall	Magic (Commander only)	Builds the whole deck	Not confirmed	Yes, source not stated	Free; paid from $6.99/month	Web

Why it happens

A language model writes the most likely answer; it does not look it up. “Charizard ex” and “Charizard V” are so close in its training text that it can mix one card’s name with the other’s attack.

It does not check any card database while it answers, unless the tool gives it one. If a card was not in what it read, it rebuilds it from something that sounds similar.

Its knowledge has a date. Pokémon Standard rotates every year and Magic updates its banned list several times a year: what was legal when it was trained may not be today.

Nobody counts the cards for it. Exactly sixty, four copies at most, the One Piece Leader on its own or Commander’s 100 are rules the text can skip without anything stopping it.

The prices it gives are from memory. Ask for a deck under €50 and it does not know what each card costs on Cardmarket today.

How to avoid it if you use ChatGPT

Ask for every card with its set code and number (for example “TWM 130”), and look it up in the game’s official card database or on Scryfall before you buy it.

Give it the format and the date: “Pokémon Standard as of November 2026, from Temporal Forces”. Even then, check the official list of legal and banned cards.

Ask it to count: how many cards the list adds up to and how many copies of each. If it is not 60 (or 50, or 100), it is not finished.

Ask it to flag the cards it is unsure about. That does not fix it, but it tells you where to start checking.

Do not trust the prices: check them on Cardmarket or TCGplayer the day you buy.

Or use a tool that checks every card against a database: Farseek (Commander) says every recommendation follows a Scryfall search, and TCGJoin’s Deck Coach checks it against its catalog. We compare them in the best AI deck builders.

How TCGJoin’s Deck Coach solves it

The Deck Coach also uses a language model, but it does not get the last word. Before it suggests anything, the model gets the game’s guide (deck size, copies, format, the structure of a winning deck) and up to 40 real catalog cards that fit your request, with their price. When there is a recent tournament-winning list for the archetype you ask for, it starts from that.

Then the server checks the list line by line against the catalog: each card is looked up by name and resolved to a real printing, the cheapest legal one. If a card does not exist, a Pokémon is missing its pre-evolution or the list is not a legal size, the server sends it back to the model with the reason so it can fix it. Whatever is still wrong after that is fixed with fixed rules: non-existent cards out, rotated cards swapped for their legal version and the deck filled up to its size.

Legality comes from each game’s official list: Scryfall for every Magic format, TCGdex for Pokémon, YGOPRODeck for Yu-Gi-Oh! and Lorcast for Lorcana. One Piece, Dragon Ball, Digimon and Riftbound do not publish a machine-readable list, so there the construction is checked (size, copies, Leader colors) and the deck says so.

Every deck gets a stamp set by the server, not the model: “Legal” with the format it was checked against (for example “Legal · Standard · 60/60”) or “Draft” if something is left to fix, with the reason. And the total price is the sum of the real cards at Cardmarket prices in euros (or TCGplayer, converted, where there is none).

What the Deck Coach does not do

It does not guarantee you will win: the meta changes every week and the tournament lists it starts from are from the last few months.

In games without a machine-readable official list (One Piece, Dragon Ball, Digimon, Riftbound) it checks construction, not the bans from the latest announcement.

The free plan has 5 AI tries; to build often you need the Rare plan, with 20 requests a day.

Frequently asked questions

Why does ChatGPT make up cards?

Because it writes the most likely text without checking a card database. If a card was not in what it read, it rebuilds it from names and effects that sound similar. OpenAI itself warns that ChatGPT can make mistakes and advises checking important information.

How do I know if a card ChatGPT gives me exists?

Look it up by its set code and number in the game’s official card database, on Scryfall (Magic) or in the TCGJoin catalog. If it does not show up with that number, it does not exist or it is from another set.

Does ChatGPT know which cards are legal in Standard?

It knows what was in its training data. Rotations and banned lists change afterwards, so it can suggest cards that can no longer be played. Always check the format’s official list.

Can TCGJoin’s Deck Coach get it wrong?

It can suggest a weak deck, but not a card that is not in the catalog: every line is checked on the server before it is shown. If something does not fit the format, the deck comes out as “Draft” and says why.

Which games does it work for?

Pokémon, Magic (Standard, Commander, Modern, Pioneer, Legacy, Vintage, Pauper and more), One Piece, Disney Lorcana, Yu-Gi-Oh!, Dragon Ball Fusion World, Digimon, Riftbound, Force of Will and Naruto.

Sources

Every fact comes from the app’s Google Play listing, its App Store listing (US and Spain) or its official website. Prices vary by country and store. Reviewed on November 1, 2026

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