Interaction Oracle

How a verdict is reached

Each card's facts say how it answers things (exile, destroy, damage, shrink, sacrifice, bounce, into the library, steal, shut off, counter, discard) and which kinds of permanent each way hits; its defences (indestructible, hexproof, shroud, ward and its cost, protection, regeneration, can't be countered); and any limits (mana value, power or toughness, type, color). For each way your card answers, the Oracle checks, in order:

• Does it hit that kind of permanent at all? A spell (instant or sorcery) is only ever on the stack, so only a counter can meet it, or a discard spell while it's still in their hand.
• Does a limit rule it out: mana value, size, type or color?
• Does a defence stop it: indestructible against destroy and damage, hexproof or shroud against anything that targets (a sweeper or a sacrifice gets past them), protection against targeting and against damage? Only protection the card has itself counts: a keyword on it, or "this creature has protection". The One Ring gives its controller protection and a Sword gives the equipped creature protection; neither card has it, so neither stops an answer aimed at the card itself.
• Is there enough damage for its toughness? A * counts as it stands, X damage is a condition, and a creature that enters with +1/+1 counters (Murktide Regent, Stonecoil Serpent) is bigger than its printed size, so fixed damage or a fixed minus against it is a condition.
• Does something make it conditional: their choice of what to sacrifice, a minus that has to reach its toughness, regeneration, protection it can gain, or a condition in the text the facts don't spell out?

Ward is a cost, not a stop. A known ward cost ({2}, pay 2 life, discard a card, sacrifice a creature) is paid, and the row says what it adds; only a cost that can't be known in advance (ward {X}, life equal to its power) makes an answer conditional.

Bounce, tap and phasing, and taking a card until end of turn, answer "For a turn": the card comes back or untaps, so it buys a turn and doesn't remove it. A card its owner puts on the top or bottom of their library, their choice (Aether Gust, Tolarian Contempt), is a maybe for the same reason: on top, they draw it again. A spell taken off the stack that way, or returned to hand (Hullbreaker Horror), is a maybe on the stack; exiling it (Mindbreak Trap) works, even on a spell that can't be countered. A color written after the noun ("target spell or permanent that's red or green") limits it like one before it. Discard is judged while the card is in their hand: a spell where you choose the card (Thoughtseize, Inquisition of Kozilek, Duress) takes it when it fits what the spell can take, and misses a type it can't take; one where they choose (Mind Rot) or that picks at random (Hymn to Tourach) is a maybe.

Then what else happens: an exiled creature never dies (so a "dies" ability doesn't fire, and undying or persist can't bring it back), a bounced card can be cast again, and a counter only works while the spell is on the stack.

Then what lasts: a card that stays on the battlefield can shut another off without removing it. The Oracle reads these from both cards' text, with the Comprehensive Rules numbers each rests on: activated abilities that can't be activated (Stony Silence and Sol Ring, Cursed Totem, Linvala; or a name chosen as it enters: Pithing Needle, Phyrexian Revoker, Meddling Mage), lands made a basic type or abilities removed (Blood Moon and Urborg, Humility), enters and dies triggers that don't trigger (Torpor Orb, Hushbringer), spells that can't be cast from a graveyard, library or exile (Drannith Magistrate, Grafdigger's Cage), more than once a turn (Rule of Law, Ethersworn Canonist) or at instant speed (Teferi, Time Raveler: a counterspell then never has a spell to counter), cards that can't enter from a graveyard or library and creatures exiled because they weren't cast (Containment Priest), cards exiled instead of going to a graveyard (Rest in Peace, Leyline of the Void), searching, life gain, draws past the first, taxes, permanents that enter tapped or don't untap, and creatures that can't attack. Each line is "Shuts it off", "Limits it" or "Doesn't reach it", with the sentence it was read from. "Shuts it off" means nothing the card does is left (keywords such as flying, which only shape how its body fights, aside): Blood Moon shuts off Urborg, but only limits Volcanic Island, which still taps for red, and Dryad Arbor, still a creature. A trigger that watches other creatures dying counts too: Hushbringer and Rest in Peace shut off Blood Artist (under Rest in Peace nothing dies at all, tokens included: each is exiled instead, CR 614.1a and 700.4). Activated abilities that can't be activated rest on CR 602.5. A kind it doesn't read is never a "no": the page says the Oracle doesn't read every lasting effect and points to the rulings, and the rulings that name both cards come first.

Working together

For the same side of the table, the Oracle reads both cards' rules text sentence by sentence into a profile: the types it names and what it does with them (pumps, counts, triggers on, tutors, makes cheaper), its mass effects and what they spare (a type, a card type, a size, flying, indestructible), what it costs and what can cut that cost, its enters and dies abilities, what it does to itself (sacrifices itself, comes back from the graveyard, has madness or cycling), and what it waits for. Then it matches one card's profile against the other's, both ways, and names each link by its kind, listed in this order:

• a two-card combo listed by Commander Spellbook;
• a cost one card cuts or skips;
• a trigger one card feeds or repeats (tokens, life, cards, counters, lands, deaths; a flicker, a copy or a doubler for an enters or dies ability);
• a wipe one card survives;
• a loop: one card uses itself up and the other brings it back;
• a type one card names (a lord, a tutor, a count);
• an ability one card gives the other;
• something one card supplies and the other uses (cards in the graveyard, mana, an untap).

The page doesn't grade links: it says what each one is and shows the sentences it was read from, and how much a link matters is yours to judge. Where the findings chain, the page lays out the line of play in order. It also lists where two cards get in each other's way on the same side: a wipe that takes yours too, a symmetric lock or tax, a flicker that misses a cast-only enters ability, graveyard hate against your own graveyard.

Pick one card and the Oracle runs the same match against every card on the site (in your browser, about a second) and lists every card with a link specific to the pair, by kind in the order above: two-card combos from Commander Spellbook first, the ones in the most EDHREC decks (Spellbook's count) first; within the other kinds, cards with more links first, then the cards more played in Commander (EDHREC rank, which counts Commander decks only). Links most cards of these types share (a card type named, as in affinity for artifacts, or a keyword given) show only when you pick both cards.

How it was checked, misses first. A set of 40 known pairs written after the first version caught 27 on its first run; the 13 misses (Entomb into Reanimate, Teysa Karlov doubling Blood Artist, and others) became new patterns, and it now catches 38 (the two left, Arcbound Ravager with Ornithopter and Sanctum Weaver with Utopia Sprawl, show only as links most cards of those types share). A probe of 80 famous pairs finds a link specific to the pair in 68; of the other 12, 5 are pure combos that Commander Spellbook finds instead, 3 show only as links most cards of those types share (Cranial Plating with Ornithopter is a known pairing the reader reaches only that way), 3 have no link in their text, and 1 name didn't match. 22 unrelated pairs (Doom Blade and Murder, Opt and Consider) show no false link, and 36 gold pairs with exact expected answers, clashes included, all pass. Because the patterns were tuned on these sets, real-world coverage is lower than these numbers.

What feeds a card: the database's join

The card database says, for each card, which classes of thing it produces (makes a token, sacrifices, destroys, gains life), what its triggers want (a creature entering, a creature dying, a life gain) and whose action a trigger watches, and what it spends as a cost. Its join table (data/layers/satisfies.json, written for this data version by the database's builder) has one hand-checked row for each produced class and wanted class that the rules connect: a trigger row (making a token causes a creature to enter), a cost row (a sacrifice paid as a cost is still a sacrifice) or a supply row (a token can pay a sacrifice cost). Each row carries its rule in words, the Comprehensive Rules numbers it rests on, whose side it reaches, the conditions under which it doesn't hold, and the pairs it was checked on by hand. Of its 76 rows, the 71 that the class facts can apply are shown; 5 need a cost read ability by ability from the card's text (a {T} cost, a mana cost, a copy being cast) and are left out.

Pick one card and the page lists what feeds it and what it feeds, one line per row, with how many cards in the chosen format (and colors) carry the other half and the list of them, most played in Commander (EDHREC rank) first. Lines stay separate by class and are never added together: Blood Artist's "a creature dies" is fed by sacrifice outlets, edicts, destroy effects, sacrifice costs and end-of-turn sacrifices: five lines with five counts, because every removal spell triggering it is true and says little on its own. A count holds only cards that pass the row's check. Each row names the checks it needs, and most can't be made from the classes alone ("When this creature enters" and "Whenever another creature enters" are one class; so are scry and surveil), so feeds_build.py reads each card's own oracle text in the database for exactly those checks: whose side an output reaches and whose action a trigger watches (a cost or a sacrifice outlet is always yours, so it never feeds "whenever an opponent sacrifices"; damage to you is not an opponent's life loss), whether a trigger watches the card itself or other permanents (a token feeds "when this creature enters" only as a copy of that card), which tokens fit ("a creature", "an artifact", a named subtype), "cast or copy" (a copy isn't cast), scry or surveil, what a damage trigger's source must be, where counters land and of what kind, which lands a land-fetcher can put, lifelink, and infect. A card whose text doesn't settle a check is not counted, and the line says how many. Pick two cards and each row that joins them, in either direction, joins the page's own links: as the rule under a link that already says the same thing in the cards' words, or as a line of its own; one interaction is one line.

A row is a fact about the rules at class level, checked on each card's words; it is not a loop search. The database's loop finder, which checks each link ability by ability, is not used here: of 3,993 known two-card infinite combos it finds a loop through 679 (17%), and in a hand-checked sample of 40 new two-card loops it reported, 2 repeat as stated, 2 more need something the record doesn't state, and 36 don't repeat. Loops stay off the site until that improves. Data version: the card database's, printed under the lists; rules: the Comprehensive Rules effective September 25, 2026.

Limits worth knowing

This is card facts and rules text, not a rules engine: layers, timestamps, replacement effects and the stack aren't simulated, and a card that targets in one mode but not another is read as targeting. The synergy reader knows patterns, not every card: an unusual wording can hide a real link, and a finding is a fact about the two texts, not a claim that the pair is worth playing. That's why each finding shows its sentences and each card's official rulings sit on the page: they're the word to check against.

The lasting restrictions are read the same way, from words: a Blood Moon row says what the rules make of Urborg, not what every later effect does to it, and a kind of lasting effect the reader doesn't know is never shown as "Doesn't reach it".

Sources

• Card facts: the site's card data (how each card answers, its defences and limits).
• Rulings: Wizards' official rulings, from Scryfall's rulings file (October 22, 2026).
• Lasting restrictions: both cards' rules text, read by the synergy reader (SY.apart), with rule numbers from the Comprehensive Rules effective September 25, 2026.
• Combos: Commander Spellbook.
• What feeds a card: the card database's join table (data/layers/satisfies.json), applied by feeds_build.py to the database's class facts and each card's oracle text in the database; rule numbers from the Comprehensive Rules effective September 25, 2026.