Why this exists.

Friends who could not get a playtester working

The first was watching friends try to play online. Not the playing — the setting up. Wrestling a playtest table into something that could be shown to a pod over a call, getting a second view running that did not show everyone your hand, doing it again next week because the setup did not survive being closed.

None of that is the game. It is furniture, and it was eating the evening before anyone cast anything.

So we made playtesting a first-class part of the product rather than a feature bolted on: a real tabletop with zones, drag-and-drop, stacks and counters, and a Streamer View that mirrors it exactly with your private information removed — your hand as card backs, face-down cards still face down. It has a temporary public link, so a second monitor, an OBS scene, or somebody else's browser all work without an install and without a second account.

An assistant that could only see one deck at a time

The second was asking an AI for commanders that would suit the way we actually play. The answers were decent. They were also generic, and it became obvious why: it was reasoning from a paragraph of self-description, because a paragraph was all we could give it.

The interesting thought was what would happen if it did not have to take our word for it. Not one decklist pasted into a chat — the whole shelf. Every deck you have built and kept, the ones you keep sleeved and the ones you abandoned at forty cards, what you reach for repeatedly and what you own but never play. That is a far better description of a player than anything they would think to write down about themselves, and it already exists. It is just locked inside a deckbuilder that has no way to be asked.

Cartheca is our attempt to unlock it properly. Not a chatbot bolted onto a deckbuilder, but a card archive whose whole surface — the catalogue, every deck you own, your collection, every exact printing — is reachable by the assistant you already talk to, over MCP or a documented API.

The deckbuilder is a real deckbuilder and works entirely on its own. It is just no longer the only way in.

Your decks are yours, including on the way out

Decks are private until you decide otherwise, and there are two separate decisions — an unlisted link, or publishing to Community — because they are not the same thing and collapsing them costs somebody their privacy eventually.

An account backup is a portable file you can create, validate, and restore. A tool that is easy to leave has to keep being worth staying in, which is the right pressure for it to be under.

Advice, not gates

An illegal deck warns you, marks the exact cards the warning is about, and then gets out of the way. Plenty of real decks are illegal on purpose — a kitchen-table brew, a list mid-rebuild, something pasted in from elsewhere and half fixed.

The one thing an illegal deck cannot do is appear in Community, because a public catalogue that quietly lists illegal decks is lying to whoever browses it. Card packages go further and have no legality rules at all, because a mana base is not trying to be a deck.

This is the workshop's name showing up in the software. Janky decks are the ones worth building; the job is making them good, not making them normal.

An assistant proposes; you decide

Every change an assistant makes to a deck is a proposal shown against your current list, including creating a deck and deleting one. You keep what you want and reject the rest. An assistant cannot approve its own suggestion.

This is the constraint the rest of the AI work is built around, and it is deliberately inconvenient. An assistant that could edit silently would be faster and would make the product untrustworthy the first time it was wrong.

Free, and not a funnel

There is no paid tier and no plan for one. Nothing in the product is held back behind a payment, and the support page says so plainly rather than treating a donation as an unlock.

Credit what it is built on

Card and printing data comes from Scryfall. Combo data comes from Commander Spellbook, which stays the authoritative source and is linked as such rather than quietly absorbed.

Cartheca would not exist without either of them, and both are named in the footer of every page for that reason.

Say the unflattering part out loud

The terms page currently states that Cartheca can lock an account and hide a deck against rules that are not published anywhere yet. That is true, it is not good, and it is written down instead of left for somebody to discover.

The same applies to the privacy page, which describes what the software actually does and refuses to imply a policy exists before one has been reviewed.

Cartheca is card and theca — a theca being the case or receptacle a thing is kept in. A card library, in other words. The archival look follows from that: parchment, copper, and forest, and a deck presented as something catalogued rather than something posted.

Cartheca is unofficial Fan Content and is not approved or endorsed by Wizards of the Coast.

The FAQ covers how the product works. Anything it does not answer goes to Contact, which reaches the people who build this — there is no support desk in between.