- Not to be confused with Reactor 1.0 or Reactor 2.0
If anything in this doc is unclear, please just ask on the Hanabi Central discord or edit it yourself!
ReactorZero emphasizes simplicity and clarity. It's powerful yet also one of the simplest convention systems.
No knowledge of Reactor 1.0, Referential Sieve, or H-group is required.
We first cover stable and reactive clues in 3-player games then discuss general conventions, 4/5-player games, and variants.
Later we include convention proposals/discussions (and a potential "learning path").
ReactorZero has only two types of clues: stable and reactive.
Every clue given to the next player is stable.
We name the player whose turn it is Alice and the subsequent players Bob, Cathy, Donald, Emily, and Fred.
ReactorZero uses the following terminology to describe the status of cards.
Card status (click to open)
A card is visible by a player if it appears in someone's else hand, in the discard pile or in the stacks or if it has full empathy. A card has full empathy if its empathy is reduced to only one card and contain only crosses derived from cards in the discard pile or in the stacks.
Playable cards are cards that can play immediately on the stacks. Playable cards can be:
- Playable-by-empathy: card's empathy, given by all combinations of ranks and colors visible on the card by pressing spacebar, only contains playable cards. For simplicity, only consider possibilities crossed out in the empathy by cards visible by all players (global empathy).
- Playable-by-signal: known to be playable by being play-signaled
- Obviously playable: playable-by-empathy or playable-by-signal.
- Playable-by-good-touch: Same as playable-by-empathy except that the card's empathy might also contain trash cards. Cards visible by the clue giver are additionally taken into account to determine which crosses are known for playable rank clues.
Trash cards are cards whose empathy only contain cards that cannot become playable in the future. A same-hand dupe is a card whose second copy appears in the same hand.
Play reveal: Any stable clue that touches a card and makes it become playable-by-empathy tells Bob that he may play that card. (No further meaning.)
Otherwise, the meaning of a stable clue depends on the clue type:
| Clue type | Meaning |
|---|---|
| Color (touching new cards) | Play leftmost newly-touched card |
| Rank (touching new cards) | In order of priority,
|
| Reclue with rank or color (touching no new cards) | Play leftmost touched card |
A locked player must not discard any card until they receive a safe action.
An unlocked player without a known or signaled action (play or discard) may discard their leftmost unclued card (their chop) instead of giving a clue.
If a card that was called to play is not immediately playable, the clue has no meaning beyond the information it provided to the hand (stall).
Every clue not given to the next player is reactive. (All of Alice's clues to anyone not Bob are reactive.)
For a reactive clue, the clue recipient is called the receiver; every player whose turn is after the clue-giver up to the recipient is called a (the) reactor.
The clue gets an action from the reactor(s) followed by an action from the receiver. When Bob takes that action, we say that Bob "reacts" to the reactive clue.
The type of action (discard or play) in both hands is determined by the type of clue:
| Clue type | Meaning |
|---|---|
| color | odd number of plays from the reactor and the receiver (1 discard + 1 play, or 1 play + 1 discard) |
| rank | even number of plays from the reactor and the receiver (2 plays, or rarely 2 discards) |
The value of a reactive rank clue is the numerical value of the rank clue. For example, if the clue were a rank 3 clue, the clue value is 3. If the clue were a rank 2 clue, the clue value is 2.
The value of a reactive color clue is red = 1, yellow = 2, green = 3, blue = 4, purple = 5. With additional colors, colors should be assigned missing values. If no colors are missing, start back from 1.
The actions (play or discard) will come from one of Bob's slots and one of Cathy's slots, respecting the equation
Clue value = Bob's slot + Cathy's slot (modulo 5)
Example:
The 5 in "modulo 5" corresponds to the number of cards in each hand.
In order for Bob to know which action he should take, Alice and Bob need to agree on which action Cathy should take. This is achieved by the following targeting priority.
Targeting priority in Cathy's hand:
Obviously playable: Whether a card is obviously playable is determined before the reactive clue is given.
Immediately playable: When Cathy is signaled a play, the targeted card in Cathy's hand must be immediately playable after Bob reacts.
Re-targeting: If the clue does not work (makes an unplayable card play or a critical card discard), the target is moved to the next possible target in the priority list. To compute the next possible target, consider what card would be prioritized if the impossible targets are ignored.
Plays (priority 1, 2, 3):
Finesses (priority 2): Only possible with rank clues as they require two plays.
Dupes (priority 4,5):
Leftmost Trash (priority 4):
Sacrifice (priority 6): To compute the furthest-away from playable, look only at the distance between each potential target and their corresponding stack. If multiple cards are furthest-away and equally far away, choose the card with the highest rank. If some of these have the same rank, choose the leftmost card. Moreover, do not sacrifice/target critical cards!
This section applies at all player counts.
Which cards are play-signaled?
To avoid desynchronization (i.e. when different teammates believe different things), cards gotten by playable rank clues, whose playability relies on cards that are not visible to some players, are not considered play-signaled.
Play signals are not generally erased if the play-signaled card might have been duped. If it is deducible (by considering all the possibilities this card could have been when it was signaled) that the play-signaled card has been duped, the player marks that card as trash.
Play-signaled cards that were actually duped can be fixed by:
A player without playable cards can discard the card with the most recent discard signal. If no cards have discard signals, they can discard their leftmost unclued card ("chop").
Discard notes only last until you draw a new card or you receive a lock clue. After a player plays or discards a card or receives a lock clue, they erase all discard signals in their hand.
A player with multiple trash cards typically discards them from left to right. In the endgame, if a player does not discard from left to the right, the clue might be interpreted as a positional discard. In any other situation, a player may choose to discard another trash card than the leftmost one, for example to keep a omni trash card.
Discard of non-trash cards without discard signals do not have any special meaning beyond giving a clue back to the team. They can exceptionally be done to generate a clue.
A card that is playable-by-good-touch is not expected to play on its own unless absolutely necessary to get maximum score.
Hard information is any information that comes from the empathy of the cards.
Soft information also includes pink promise and the possible identities of a play-signaled card (without taking into account targeting priority).
The meaning of a clue can only be overriden by hard information.
It is not expected that players deduce any information beyond soft information. These extra deductions form contextual information (targeting priority, elimination notes, not given clues, ...). Players should in general refrain from taking any action (play/discard) from contextual information.
It is Alice's job to save Bob's chop.
Alice assumes that Bob might discard their chop (if Bob does not have a safe action) even if there is a critical card on Cathy's chop.
The endgame starts when the pace is strictly less than the number of players.
(At pace 0, everyone must play a card on the last round to achieve the maximum score; at pace x, x players don't have to.)
Positional discards are only possible in endgame and get the last possible player to play the matching slot. A card gotten by positional discard is not considered play-signaled.
A positional discard is not always possible, e.g. if it would look identical to discarding chop. Assume generally that Alice is discarding her leftmost locally known trash over a positional discard.
The players should try their best to avoid lines that do not get the maximum score. Reactive clues that lose on the spot should be reinterpreted to satisfy that condition. Playing a card from context might also be necessary.
Cards are targeted as if there would be more turns to play. If a hand has less than the maximal amount of cards, the slot numbers are counted from left to right starting at slot 1.
The next player must ignore the reaction and proceed as if they were locked for that turn. The entire reaction chain is off including the reactor and the reactor should not try to correct their mistake by reacting later.
The targeted card is no longer considered signaled.
If a player discards chop or a trash card when they have a play-signaled card, if it was an "obvious" mistake from that player, their play-signaled cards are no longer play-signaled otherwise the signaled is still on. This convention is subject to many interpretations on what could be considered an obvious mistake. Feel free to suggest alternatives in the convention proposal section.
While receivers occasionally delay their actions, only rarely should reactors delay.
The receiver can delay their action by giving a clue or by playing a different card. In this case, the targeted card in the receiver's hand is signaled.
A reactor can delay their action by giving a clue, but in this case, the signal to later players is lost (e.g. Cathy does not try to figure out what was the meaning of the clue when Bob reacts later).
The reactor marks their card and is expected to react to the clue later, but the reactor's card is not considered signaled for targeting purposes.
When a player delays with a play-signaled card, it is mandatory for that player and the player positioned before them to remember/mark all playable possibilities for that card (omitting targeting priority inferences). This information should be used later to determine if the card is still playable, became trash or needs a fix.
Only the most recently given reactive clue, if there are multiple reactive clues given before your turn, is "active".
This section is only applicable when playing a game with special suits. For more on variants, see the variants page.
On hanab.live, to attempt to play an inverted card, drag it to the stacks: the card will discard. To attempt to discard an inverted card, drag it to the trash: it will play.
4p and larger games can be significantly harder than 3p games.
As in a 3-player game, Alice's clues to Bob are stable.
Alice's clues to Cathy are reactive like in a 3-player game. Since each hand contains 4 cards in a 4-player game, the equation involving the clue total is changed to
Clue value = Bob's slot + Cathy's slot (modulo 4)
All clues to Donald are double reactive. They get an action from Bob (the first reactor) followed by an action from Cathy (the second reactor) followed by action from Donald (the receiver).
| Clue type | Meaning |
|---|---|
| color | odd number of plays (3 plays or rarely 1 play) |
| rank | even number of plays (2 plays or very rarely 0 plays) |
The equation is
Clue value = Bob's slot + Cathy's slot + Donald's slot (modulo 4)
The target in Donald's hand is fixed before determining targets in other hands.
For targeting purposes, the status of cards in Donald's hand (playable,one-away,etc) is determined before any reaction occur (see discard re-targeting). For example, as Cathy, a one-away card in Donald's hand remains a one-away card even if Bob's reaction makes it playable.
If Donald's target is an X-away card, Donald's target forces connecting targets in other hands to make Donald's finesse work. The connecting target(s) is(are) assumed to be the leftmost copy on the latest player(s).
The clue is then reduced to a reactive clue between hands with unassigned targets.
Re-targeting refers to changing the card you target.
A play target is a card that would be signaled to play. This includes X-away cards. A discard target is a card that would be signaled to discard.
A card in a hand H that has just been targeted by the current clue prevents targets of the same suit from being play targets in hands occuring before H. Skipping over these blocked targets does not constitue re-targeting.
Do not re-target a play target for another play target to the right in any hand except Cathy's hand. If the clue does not work (makes an unplayable card play or a critical card discard) or if there are not enough plays remaining to make the target play as a finesse, try re-targeting on Cathy. If no re-targeting on Cathy make the reciever play their targeted card, change the reciever's target directly to the discard target with highest priority.
When re-targeting, preserve in priority the targets of the player that are the furthest-away from you.
A playable different hand-dupe is considered playable. As an exception, the card has the same priority as trash cards if its copy has just been play-signaled by the current clue in the hand of a later player.
6-player games follow the same guidelines in principle.
Clues to Bob, Cathy and Donald have the same meaning as in a 4-player game.
Discard re-targeting, playable different-hand dupe from 4-player games also apply in larger games.
All clues to Emily are triple reactive. They get an action from Bob (the first reactor) followed by an action from Cathy (the second reactor) followed by action from Donald (the third reactor), followed by an action by Emily (the receiver).
| Clue type | Meaning |
|---|---|
| color | odd number of plays (3 plays or very rarely 1 play) |
| rank | even number of plays (4 plays or rarely 2 plays or almost never 0 plays) |
Clue value = Bob's slot + Cathy's slot + Donald's slot + Emily's slot (modulo 4)
The target in Emily's hand is fixed before determining targets in other hands.
For targeting purposes, the status of cards in Emily's hand (playable,one-away,etc) is determined before any reaction occur (see discard re-targeting). For example, as Cathy, a one-away card in Emily's hand remains a one-away card even if Bob's reaction makes it playable.
If Emily's target is an X-away card, Emily's target forces connecting targets in other hands to make Emily's finesse work. The connecting target(s) is(are) assumed to be the leftmost copy on the latest player(s).
The clue is then reduced to a reactive clue between hands with unassigned targets.
This space is reserved for optional conventions and proposals so they can be referred to before the game.
(obv=non-obv): Drop the distinction between obviously playable cards and non-obviously playable cards.
(highest sac): Sacrifice highest non-crit instead of furthest-away from playable.
(no finesses): Disallow finesses.
(slot for color/rank): the value of a reactive clue is the slot number of the leftmost touched (newly or not) card, ignoring slot 1; if slot 1 is the sole slot touched (newly or not), the value is 1.
(ptd): Alice is not allowed to discard if Bob does not have a safe action and Bob's chop is playable or critical. Alice determines if Bob has a safe action and if Bob's chop is playable at the moment Zelda (the player before Alice) took her action. This means that if Zelda plays the same card as Bob's chop, Alice does not have PTD unless Alice can determine that Zelda knew about her card.
(gentleman/sarcastic discard): Discards of known cards without discard signals follow the same conventions as in Referential Sieve.
(zscp): zero clue state promise from referential sieve.
(referential play clues): stable color clues (touching new cards) mean play the first unclued card left of the leftmost newly-touched card, pretending the clue didn't touch slot 1; if it touched slot 1 only, play the rightmost unclued card.
(slot 1 finesse priority): Prioritize slot 1 on the reactor's hand over leftmost on the reciever's hand.
Level 0: Play a 2-player game with the variant 4 Suits. Only stable clues are required.
Level 1: Play a 3-player game of No Variant with the simplified targeting priority in Cathy's hand: <uplay leftmost playable play leftmost one-away discard leftmost trash or same-hand dupe</u.
Level 2: Play a 3-player game of No Variant with the standard targeting priority in Cathy's hand.
Level 3: Play a 3-player game of Omni (5 Suits). Familiarize yourself with pink promise for play clues and locks and the fact that lock has precedence over playable rank in pinkish variants.
Level 4: Play a 4-player game. Learn the targeting priority in Donald's hand, how to compute finesses dependencies in Bob's hand and Cathy's hand. (If Donald has a one-away card, it is almost impossible to make Donald discard. Learn the discard re-targeting convention.) Different-hand dupes are much more common in 4-player games.
Level 5: Play a 5-player game. Learn the targeting priority in Emily's hand and continue finding dependent targets for finesses and following the discard re-targeting convention for targets in Donald's and Emily's hand.