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Turbo is a convention system for specifically 2-player Hanabi. It inherits most of its structure from Referential Sieve, with one major twist: Turbo is a discard oldest system.
Turbo's primary innovation is the Unloaded Chop Move, which essentially allows us to import the biggest benefit of discard-newest systems into a discard-oldest context. Namely, that cards on chop can be easily saved as a side effect of other clues. The result is a very strong 2p convention system that I believe outperforms all other well-known human-playable 2p convention systems as of January 1, 2026.
For those trying to learn the system from scratch, the first two sections should be sufficient to get started: Basic Terminology & Principles and Basic Conventions. Then when you start to run into situations that seem undefined, the Advanced Conventions (the bulk of the document) are there to help, and are conveniently organized by topic.
The prose in this document is meant to convey the most important aspects of a convention as concisely as possible. Often, this means intentionally underspecifying conventions to make their description simpler. However, if this choice proves to be unpopular or unwieldy, it may be changed in the future. Please feel free to give feedback on any conventions you find unclear, or whose wording can be improved.
If you are a returning player looking for a summary of convention changes, see the Changelog at the end of this document.
Huge thanks to everyone who contributed, knowingly or not, to Turbo's development!
Maintainers: Doodles (sjdrodge), sodiumdebt
Contributors: Estabir, florrat, hallmark, kimbi, Libster, Noah, timotree
Indirect contributors: Floriman, Lel0uch, pianoblook, piper
The card that a player is expected to discard once they run out of explicitly promised safe actions.
Usually abbreviated PTD. Once a player with a Chop is left without an explicitly promised safe action, they gain PTD for the card that is on Chop.
A player is considered Loaded when they already know about a safe action. PTD counts as a promised safe action.
Whenever a card is saved without being touched by a clue.
Giving a safe action to an Unloaded player implies that the card on their Chop might be good. In this system, we explicitly Chop Move that card. This is our most fundamental principle. Any situation where it doesn't apply will be explicitly noted.
Cards that have been touched by clues are generally assumed to be useful cards. See Good Touch Play Policy for additional information.
All the unclued cards have a discard precedence (used for interpreting otherwise ambiguous discard clues). To rank them from highest to lowest, start with the card on Chop, then proceed leftwards and wrap around until you get back to Chop.
aka CCC or Triple C. Once a card has been explicitly instructed to either play or discard, or given PTD, it is considered clued.
When a player has no cards that are safe to play or discard.
The most fundamental conventions. Enough to start playing.
Every card except the leftmost card in both player's hands starts Chop Moved.
Any clue that directly fills in a previously clued card as Trash or Playable is focused solely on the filled in cards and does not trigger any conventions other than Unloaded Chop Move Principle.
Number clues are left-referential discard clues by default. Meaning, mark PTD on the unclued card to the left of the newly clued card. If there are multiple such candidates, mark PTD on the candidate with the highest Discard Precedence that wasn't already on Chop.
Notes:
When all the cards of a particular number are playable (e.g. 1's at start of the game), cluing that number does not indicate a discard. Instead, it indicates that all the clued cards are playable.
Notes:
Color clues are play clues that "push" the previously-unclued card to the left of the newly clued card. If there are multiple such candidates, play the leftmost candidate.
Notes:
The rest of the conventions are organized by topic. Conventions in this section are assumed off in beginner games and on in expert games.
This section covers clues that only touch previously clued cards.
A reclue which does not fill in any new information calls for two plays. The first play is always the leftmost unclued card. The second play is chosen with the following precedence schedule:
Important notes:
If filling in cards reveals that another card is Immediately Playable while at least one of the reclued cards is Delayed Playable, then the clue is focused solely on the filled in cards and does not trigger any conventions other than Unloaded Chop Move Principle.
If a Reclue provides Negative information revealing 2+ Safe Actions, and a single direct Reclue could not have done the same, then the clue has no additional meaning and does not trigger any conventions other than Unloaded Chop Move Principle.
Filling in Unplayable cards that are either Critical or a 2 calls for a blind-play of the leftmost unclued card.
Note: Cards told to play this way are Immediately Playable.
Filling in Unplayable cards that are neither Critical nor a 2 Chop Moves all unclued cards and communicates a Lock. However, your partner will often immediately unlock themselves by discarding the clued card (or any other card).
Note: Since Locking a Loaded player doesn't make sense, giving this kind of clue to a Loaded player is a Loaded Fill-in Bluff instead.
Cluing color to a PTD card means play if the card could have become playable since it was given PTD. Otherwise, it revokes the PTD and calls the leftmost unclued card to play.
This section covers giving number clues to previously unclued cards.
When all of the cards of a particular number are trash, clues using that number are treated like Color Pushes.
Any number clue to a new card which reveals an already clued card as playable via Empathy + Good Touch Principle, then the clue has no additional meaning and does not trigger any conventions other than Unloaded Chop Move Principle.
This section covers situations where a player has multiple known Safe Actions to choose between.
If you have both a known play and a known discard, choosing to discard causes a Chop Move.
Notable Exception - If your only playable card just became playable by Good Touch Principle due to your partner's blind-play, you are allowed to take a signaled discard without triggering this convention. This gives your partner an opportunity to fix a card that they couldn't predict was going to bomb.
Players may freely choose between cards with different Empathy without conveying information. However, players are expected to play cards with identical Empathy in "Focus first, then 15432" order, unless they are 1's, in which case 1's Play Order applies instead.
As an exception to Play Order, players are expected to play clued 1's with identical Empathy in "Chop first, then left-to-right" order.
Note: Chop only comes first if the 1's clue is given to an Unloaded player.
Players are expected to discard Empathy trash first, conventionally promised trash second, and PTD last. Within these categories, players are expected to discard right-to-left.
Note: With multiple PTD, players are allowed to discard whichever card they believe is most likely to be trash.
When choosing between multiple plays or multiple discards, skipping forward through the order causes a number of Chop Moves equal to the number of skips.
Note: Playing 1's out of order does not Lock a player if it can give PTD instead. Specifically, the Excessive Chop Move PTD convention is triggered by one fewer Chop Move than usual.
When a Free Choice convention would indicate more Chop Moves than the number of unclued cards that can be Chop Moved, it Chop Moves all of them, but it also gives PTD to the previously Chop Moved card that is n-th in Discard Precedence where n is the number of excess Chop Moves. There are two conventions that can reduce the number of Chop Moves required to be considered "excessive." See Unlocked Starting Hands and Order Chop Move for details.
For example, suppose Alice has y5 b5 (g4) (g2) [r4] (g4 and g2 are Chop Moved and r4 is clued), and Bob takes an action which indicates four Chop Moves. Alice will Chop Move both y5 and b5 and mark PTD on the g4.
When a player knows about a safe action that has not been conventionally promised, demonstrating this private knowledge generally doesn't trigger Free Choice conventions. Notably, it can still trigger Unlock Promise and Zero Clue Safety Promise.
This section covers conventions that uniquely apply near the beginning of the game.
If a player has multiple 1's in their Starting Hand and all of them are good, it is expected that they will receive a 1 clue instead of a Color Push. When a player later finds out that they held starting hand 1's that were not clued this way, they should assume at least one of them is Trash.
We pretend that the first turn of the game is not an eight clue turn, and therefore no Eight Clue conventions apply.
Note: This means that Unloaded Chop Move Principle applies even though you are forced to clue.
There is an assumption that each player's Starting Hand cannot be Locked. This means that a Number Discard targeting Chop on the first turn of the game just means to discard Chop instead of indicating a Lock. It also affects the Excessive Chop Move PTD convention. Namely, it takes one less Chop Move to trigger the convention.
Cluing 4 to a Starting Hand is not usually a Number Discard. Instead it just means to discard the 4 that was hardest to target with a Number Discard. However, if none of the 4's could've possibly been difficult to target, then the clue should be interpreted as a regular Number Discard after all.
y3 is played and you hold two yellow cards, one of which has Negative 4.)Note: As described in the Shout Discard section, you can give your partner a turn to Fix if their blind-play suddenly creates one of the above situations.
When a player has 2+ clues on their turn they must not give PTD to the following:
This has the following consequences:
Notes:
Discarding an immediately playable card promises that card in partner's hand: either among the cards that are already queued to play, or in the rightmost possible position.
Note: Unloaded Chop Move Principle does not apply to Gentleman's Discards.
It is generally assumed that cross-hand duplicated 2's are treated as trash, while 3's and 4's are not. Players are allowed but not required to discard duplicated 3's and 4's.
If a Number Play only touches the leftmost previously unclued card, then it was usually possible to give a Color Push instead. Therefore, such clues gives PTD to the second leftmost previously unclued card. This does not apply when a PTD card is already present, because color may have been avoided purely to avoid revoking.
Giving a clue that reveals the Connection of an Immediately Playable card you are globally known to hold asks your partner to Lock for one turn while you play the Connector.
Note:
This section covers clues given to a player who already knows about a safe action.
Number clues to Loaded players are right-referential play clues by default; that is, they indicate a play on the previously-unclued card to the right of the newly clued card. If there are multiple such candidates, play the rightmost candidate.
Notes:
When a player is loaded only with PTD, Right-Referential Number Clues that target cards which were drawn after the PTD was issued indicate a discard (marking a new PTD) and revoke the existing PTD.
If the PTD card itself is touched by a number clue, it nominates the leftmost previously-unclued card drawn since the PTD was issued. If there is no such card, it nominates the previously-unclued card to its right instead. Include these nominees along with any Right-Referential nominees. The rightmost of the nominees is the target of the clue.
When the target of a Right-Referential Number Play cannot possibly be playable, but at least one of the newly clued cards can, it should be interpreted as a direct play signal on the rightmost newly clued card instead.
You cannot give a Fill-in Sacrifice to a Loaded player, so any fill-in Reclue to a Loaded player calls for a blind-play of the leftmost unclued card.
Note: Cards told to play this way are Immediately Playable.
Cards with PTD are treated as clued per CCC and are therefore skipped over by all referential clues. See Direct PTD Revokes for clues that touch a PTD card.
This section covers situations where the team has zero clue tokens.
At zero clues, choosing to discard a clued or Chop Moved card instead of a known safe discard or known play causes a Chop Move.
At zero clues, if you have the opportunity to perform a Shout Discard or a Sacrifice Shout using a known Non-critical card, declining to do so gives PTD to your partner's Chop.
When you choose to spend the last clue token, you should have a plan for how to exit zero clues safely. This requires that one player discards or plays a 5 to gain a clue token while their partner has a known Safe Action.
If exiting zero clues safely might require your partner to perform a Shout Discard, then your clue promises that they hold a Non-critical card. If your partner has a new Chop (after Unloaded Chop Move Principle is applied), it is given immediate PTD. Otherwise, your partner is given permission to sacrifice their clued or Chop Moved card that is least likely to be Critical.
This section covers situations where one player is signaled that they have no Safe Actions.
Unloaded Chop Move does not apply to any clues given by a Locked player.
Intentionally playing known Trash or a card with PTD when your partner is Unloaded communicates that they are Locked.
When your partner is Locked, if you play a card that might unlock them while you have an alternative Safe Action that definitely doesn't, you promise that the Connection is in the rightmost possible position in their hand.
Certain actions never Unlock Promise:
- Discarding a card.
- Playing a 5.
- Playing an unknown card.
- Playing a card whose Connection is known to be in your own hand.
- Playing a card whose Connection is guaranteed not to be in your partner's hand.
Other actions are candidates to unlock promise; however, for the convention to work, the unlocked player must always have at least one available action that does not Unlock Promise. Therefore, when all actions are potential candidates, the card that became known Playable earliest is treated as though it were not a candidate.
Players are expected to Unlock Promise their partner ASAP. Therefore, both players are expected to write notes based on declined opportunities to Unlock Promise. For example, if a player could have Unlock Promised by playing y3 but chose not to, both players should mark the card that would have been Unlock Promised as !y4. Future Unlock Promise opportunities with y3 will therefore signal information to another card.
When you are Locked, there are two ways to get your partner's leftmost unclued card to play:
Other color clues are considered Stalls.
When you are Locked, Right-Referential Number Clues are turned off. Instead, number clues to previously unclued cards are interpreted as Number Discards, with three exceptions:
When you are Locked, a reclue that only touches cards that are Critical, a 2, or already known to be Non-critical should be interpreted as a Stall, and therefore has no meaning beyond giving PTD to Chop. However, a Reclue that reveals a card as Non-critical should be interpreted as a normal Fill-in Sacrifice.
Note: Declining to fill in a card while Stalling can prove that it is Non-critical and/or not a 2 for future Stalls.
When you are Locked, discarding a useful non-duplicated card from your hand after having already given at least one Stall clue communicates that your partner is Locked and should Chop Move their whole hand.
This section covers situations where the team has eight clue tokens.
Unloaded Chop Move does not apply to any clues given while the team is at eight clues.
Reclues work identically to Locked Hand Stalls.
These work the same as standard Number Discards with two exceptions:
Discarding to eight clues does give your partner PTD if they are Unloaded.
Playing a card while at eight clues does not give your partner PTD. However, if your partner is Unloaded, it gives them permission to bomb their Chop so that they can use the Bomb Lock convention.
If you are at seven clues immediately after your partner spent a clue at eight clues, and you have no cards to play, you may give a Stall clue yourself as though the team were still at eight clues. This prevents situations where one player would be forced to clue repeatedly.
A card which can successfully be played. We use two different concepts of playability:
A card which can never successfully play, neither now nor in the future. This happens when a duplicate of the card has already successfully played, or when the card is unreachable due to the contents of the discard pile.
When there is only one remaining copy of a Non-trash card, it is said to be Critical.
Known Playables, Trash, and cards with PTD are always considered Safe Actions.
When the team is trying to avoid blindly discarding cards as they come out of a Zero Clue state, cards that are known Non-critical are also considered Safe Actions.
Refers to the information known about a card strictly from clues that did and did not touch it. The Empathy from clues that did not touch the card are often called Negative Empathy. The term is also often used in combination with other terms: e.g. Empathy Playable refers to a card which is known Playable without using any conventional knowledge.
A clue that proves a previously Good Touched card is actually Trash.
A clue that only touches card that have already been touched by previous clues.
A clue that is given primarily so that a player can avoid discarding or playing. Most relevant in Locked Hand and Eight Clue situations.
When one card plays into another card, we call the first card the Connector and the second card the Connection. e.g. y3 is the Connector for y4, and y4 is the Connection for y3.
The cards that are dealt to you and your partner at the beginning of the game.
Notes that are written on candidate cards when an action promises a player that they hold a card somewhere in their hand, but doesn't promise a specific location. Players are expected to "lock in" the identity of a card once there is exactly one card left that could possibly match the Elimination Notes.
This section includes common questions about the system and clarifications about the interactions between conventions that are unwieldy to put in the main document.
Coming Soon
This section includes principles that are useful for designing the conventions, but are not necessary for playing them.
The two most played chop policies in Hanabi are discard-newest and discard-oldest.
Discard-newest has the following advantages:
g1. There are now two other copies of g1 that have just become trash. Are they more likely to be among the cards that were already in your hand, or are they more likely to still be in the deck?Discard-oldest has the following advantages:
We have tried to create a new chop policy that combines the best of both worlds. We do this by picking a policy that is fundamentally discard-oldest and then building in mechanisms to get the two advantages of discard-newest anyway:
Coming Soon.
Coming Soon.
Many other systems have a policy that clues are focused on newly touched cards even when they fill in previously clued cards in an immediately actionable way. The upside of such an agreement is that clues have a higher raw efficiency in terms of cards played per clue given. However, experience has shown that being able to communicate immediately actionable information without your clues getting blocked is on balance more important than raw efficiency in 2p.
Many other systems require players to play known cards in a specific order so that deviating communicates something specific. We think most formulations of this convention are far too restrictive and too frequently force players to play suboptimal cards.
However, we do play a very restricted form of this convention in Locked Hand situations, i.e. Unlock Promise. It is possible other suitably narrowed versions of this convention could be added later.
Many other systems have a convention where telling partner about a known Unplayable card calls for the Connector to be played from among the already clued cards. We prefer to use such clues to call for potentially unrelated blind-plays because this means the convention simply comes up more frequently.
Many other systems have a Good Touch Principle that comes with much stronger guarantees than ours. Examples include:
r3 is played and a player holds two red cards, many systems have a specific location from which the r4 should play in the absence of a Fix Clue.We prefer our weaker Good Touch policy for a few reasons:
This is an age-old debate in 2p. We do not like being obligated to save 2's in every position. Here is a non-exhaustive list of scenarios where you might not want to save a unique 2:
As a result we do not automatically write conventional elimination notes for unique 2's. This does not strictly forbid players from making reads related to discarding a unique 2. However, they do so at their own risk.
This section covers ideas that have not been incorporated into the system yet.
We use the following priority for interpreting color clues (locked hand):
None of these color clues chop move, however they may save the chop if they touch it.
A history of convention changes since "release" in January 2026.