What the beta does—and what it does not.

How does Arcanum match my collection to decks?

Recipe matching is a quantity comparison. Arcanum normalizes card names, excludes basic lands from acquisition totals, and compares the quantities in your active library with each sourced recipe. The owned percentage is not an opinion about deck quality.

Guest Brew asks the server for a bounded set of companions derived only from indexed public recipes. Repeated co-occurrence, a nearest matching indexed recipe, or the exact recipe you selected provides the candidate pool; current cached-or-refreshed card metadata then enforces format legality, Commander color identity, copy limits, and the default known-combo filter. For an admitted tester, Commander suggestions can also use current EDHREC commander signals and owned quantities. These paths do not infer arbitrary combos or understand every rules interaction.

What does Analyze deck actually reason about?

The saved-deck analyzer is deterministic. After resolving cards with Scryfall data, it checks format legality, Commander color identity, copy and section limits, deck size, mana-curve, colored mana-source and role gaps, commander and recipe priors, repeated co-occurrence and feature tags, selected power target, combo preference, and ownership settings. Format-source evidence and fit for the selected power target share the format-specific scoring family. It evaluates a bounded pool of up to 240 candidate identities and returns at most 20 ranked additions, each with scorer evidence.

This is useful heuristic scoring, not proof that two cards form a combo or that a deck will perform at a particular table. Unresolved cards and blocking validation errors can prevent a recommendation. Review changes yourself.

How does Arcane Draft work?

Arcane Draft is a fast, card-first way to shape a deck. Use a mouse, touch, the visible buttons, or the keyboard: left passes a card for the current session, right adds a smart quantity, Space inspects the artwork and rules, and U undoes the last choice. The same Collection filters for mana color, mana value, card type, land type, role, legality, copies, and price sorting determine the owned-card pool.

My collection deals filtered cards you own. Smart picks and Missing cards use bounded public recipe signals around the active Brew; they are recommendations, not proof of a combo. Smart quantities respect the current format and available copy room. Activated members' accepted changes are saved to the active deck, while Guest Brew and pass history remain device-local. Price estimates may be missing or stale and never determine legality.

What do the Brew settings mean?

Saved Brew supports Commander, Standard, Casual 60. Casual, Focused (the default), and Optimized change the scorer's land, curve, role, interaction, and high-friction-card targets; they are not certified table power levels. Casual 60 checks Arcanum's casual structural limits, not tournament rotation, ban-list, or event eligibility.

Owned cards only proposes no unowned copies. Prefer owned favors your inventory and, by default, permits at most 10 missing cards across the active deck. Open card pool removes that acquisition cap while still showing ownership. Known infinite-combo edges come from a small reviewed list and are excluded by default; this is best-effort filtering, not a guarantee that a deck contains no combo.

Is AI building every deck?

No. Public recipes, collection matching, Guest Brew, and the deterministic card guide work without a language model. Arcanum AI is an embedded workspace across Collection, Discover, Brew, and History for eligible testers when the operator has enabled and configured it. The header shows which page and selected card, recipe, deck, or import it understands. An activated member can complete up to 3 AI turns per day, with one request in flight at a time; the beta shares a global limit of 100 calls per day.

Contextual guides and facts do not spend an AI turn. A model call starts only after you choose a prompt or write one. Profile controls are hard boundaries; conversation expresses softer intent. Each AI turn first saves the current draft and runs deterministic analysis. The server resolves page identifiers itself, and the model receives the saved deck, calculated gaps, bounded current-page facts, a rolling summary plus the six most recent messages, and only server-allowlisted additions and cuts. The complete answer is schema-checked and revalidated before display; it is never streamed or applied automatically. You must select card changes and choose Apply selected, and the server checks them again.

The guided journey follows page navigation and attaches to a saved deck when needed. Switching saved decks loads an isolated journey for that deck. Arcanum retains at most 40 messages and expires the journey 30 days after its latest activity. Start over deletes it immediately. If AI is paused or its allowance is exhausted, saved history and deterministic guidance remain available. Guests receive deterministic Guide mode without a model call. Arcanum AI can still be wrong and is not a Magic rules judge.

What deck-list files can I import?

The in-browser Brew importer accepts UTF-8 text and CSV up to 256 KiB, 200 parsed rows, and 250 submitted cards. Saving uses a separate JSON API body limit of 48 KiB. Text rows use a quantity and card name, such as 1 Sol Ring or 4x Opt. CSV needs a Name or Card Name column; Quantity, Qty, or Count and Section, Board, or Category are optional.

Commander, Main, Sideboard, and Maybeboard are recognized. A saved Maybeboard is limited to 50 cards. Official Standard rules require at least 60 main-deck cards and impose no rules maximum; during this beta, Arcanum stores at most 75 active main-deck plus sideboard cards for Standard or Casual 60. Casual 60 uses exactly 60 main cards, and both formats allow up to 15 sideboard cards within that active storage cap. Commander uses 100 active cards and no sideboard. Partial decks can be saved, and one tester can retain up to 30 saved decks. JSON deck imports are not supported.

Which collection exports work, and what are the limits?

Collection import accepts text and CSV files up to 5 MiB; the collection API independently rejects a JSON request body over 6 MiB. Text rows use quantity plus card name with optional [SET] collector-number. CSV recognizes card-name headers Name, Card Name, Simple Name, or Product Name; quantity headers Quantity, Qty, or Count; plus optional set code, collector number, and Scryfall ID fields. JSON files are not supported.

One request can contain 1–10,000 rows, 1–10,000 copies on a row, and no more than 100,000 physical cards in total. An account can retain at most 10,000 collection rows, 100,000 physical cards, 1,000 import batches, and 25,000 import-item rows. Undo records still count toward the durable history limits.

Shared-library safety caps are 20 active shared libraries owned by one account, 50 memberships, 50 contributing collections or members per shared library, 50 active invitations, and 2,000 lifetime invitations.

The “Official product” picker loads a published MTGJSON product list; it does not verify that you bought or still own that product. An import started while viewing a shared library still changes only the importing member's personal collection, and only that import's author can undo the batch.

How are card and deck values estimated?

Arcanum keeps two different price concepts. A supported ManaBox-style CSV can include Purchase price and purchase currency; a USD value is retained as the player-supplied historical cost. Marketplace estimates are refreshed separately from Scryfall's current USD pricing fields.

Collection cards can be sorted by unit market value. Brew shows an estimated active-deck total, price coverage, missing-card estimate, value sorting, a curve/source/role readout, and TXT or CSV export. These are estimates, not offers or appraisals: printing, finish, condition, language, seller, shipping, and market movement can change the real cost. Arcanum currently collapses playable ownership to a canonical card identity, so a mixed-printing collection total uses the representative resolved printing rather than valuing every physical printing exactly.

TCGplayer purchase links appear only when Arcanum has an approved affiliate configuration. They are labeled as affiliate links, and Arcanum may earn a commission without changing your price. Without that configuration, Arcanum shows cost estimates but no purchase link.

Price refresh is explicit, rate-limited, cached for 24 hours, and bounded to 750 collection and saved-deck identities at a time. If a large account reaches that bound, run it again to continue. Missing or stale prices remain visibly unpriced rather than being treated as zero.

Can I playtest, export, or share a deck?

Brew includes a solo tabletop sandbox for goldfishing a deck: shuffle, draw, mulligan, advance turns, adjust life, tap cards, add counters, and move cards among hand, battlefield, graveyard, exile, and command zones. The sandbox is intentionally freeform—it is not a rules engine, opponent simulator, or live multiplayer table—and its current game state stays in that browser.

The Analyze view can copy or download a text or CSV list. Activated testers can publish a versioned deck snapshot as private, unlisted, or public. An unlisted deck is available only to people with its link; a public deck may later appear in community discovery. Shared pages show the saved snapshot, not later edits, and signed-in beta members can copy it into their own saved decks.

What is the difference between Add and Safe sync?

Add to current sums the submitted quantities into your personal collection. Use it for a genuinely new purchase or a non-overlapping export. Importing overlapping exports can double-count cards.

Safe sync sets your personal collection to the complete submitted snapshot. Use it only when the file represents the whole personal collection you want Arcanum to show. An exact normalized re-import in the same mode is detected as a duplicate; file name and row order do not make it new.

What happens when a card cannot be resolved?

Arcanum checks its metadata cache first, then asks Scryfall for unresolved collapsed card identities in paced batches of up to 75. One collection operation will attempt at most 750 unresolved cards. Arcanum sends the identifiers or names needed for resolution, not your site-scoped identity or owned quantity. A temporary Scryfall failure or an ambiguous name can leave a row unresolved; it is not silently replaced with a guessed card.

How does Arcane Binder remember my place?

Lens shows one full, unaltered card at a time; Binder and Inventory use bounded pages so even a large collection does not mount thousands of cards at once. Guided shelves use facts Arcanum can explain: recent positive imports, cards that were unseen when the Binder session began, repeatable Oracle-text triggers, owned legendary cards, cards absent from your saved deck plans, visible mechanics shared with the active Brew, and your device shortlist. “Hidden engine” and “Complements brew” are heuristic discovery labels, not confirmed combo claims.

The selected view, shelf, and shortlist are remembered in local browser storage. The last card, chapter position, and explored cards use per-tab session storage. This state is scoped to the signed-in identity and active library, is not synced to other devices, and is not included in account export. It stores bounded card keys and interface settings—not images, Oracle text, or your full collection. Use Clear browsing state in Arcane Binder on shared devices; signing out alone does not clear it.

Does Arcanum store the files I upload?

Arcanum does not retain the original collection file as a downloadable blob. It stores normalized card rows and import provenance needed for quantities, duplicate detection, attribution, and undo. That record can include the source file name and an original per-row card label alongside its normalized identity. Saved account decks are stored until you delete them or delete your account.

Guest Brew keeps its current deck only in per-tab browser session storage and does not send that state to an account. For activated members, the working Brew—including its cards, deck name, source references, and build preferences—also uses identity-scoped per-tab session storage so an unsaved edit survives refresh. It is device-local, is not synced or included in account export, and reaches the server only when you choose Save, Analyze, or Arcanum AI. The Arcanum AI column width and collapsed state are also device-local preferences. Your light or dark appearance choice is a site-wide preference kept in local browser storage; until you choose one, Arcanum follows the device color-scheme preference. Closing that page session or clearing site data removes its temporary state; signing out alone may not.

Arcanum AI journeys are different: player messages, bounded page-context snapshots, and normalized, validated responses are stored with the saved deck so they can follow you across devices. They use a 30-day rolling expiration and are included in account export and deletion. Arcanum does not store raw OpenAI request or response bodies.

How does the controlled beta work?

Public recipes and Guest Brew do not require admission. The controlled cohort has 100 seats. Signing in supplies a site-scoped ChatGPT identity and can admit you directly when admissions are open, capacity remains, and nobody is waiting. Otherwise you can join the waitlist; promotions are first-in, first-out and the operator can trigger a promotion email with tracking disabled. Unpromoted waitlist entries expire after 90 days.

A promoted or directly admitted tester begins in pending status and has 7 days to commit a first collection import. That import activates the seat. If the window expires, the seat becomes available again. An administrator can revoke access and may restore an expired or revoked tester only while capacity remains. Leaving the waitlist is available from the status card.

Pending access covers collection import so you can activate; active private access adds shared libraries, ownership matching, and saved decks. Arcanum AI has a separate readiness switch and may remain unavailable even when private collection access works. This is a free, unofficial fan-content beta; features and limits may change as testing teaches us what is sustainable.