Hanabi is a cooperative card game for 2-6 players with mechanics similar to solitaire. The trick is that you can't look at your own cards and have to give clues to each other to convey information. A more detailed explanation of the rules are here.
Hanabi is one of my favourite games. It's surprisingly complex and involves a lot of higher-order thinking: stuff like "I think they did this because they thought I thought this was happening, but is it?" I've been playing it regularly for a few years now and have spent a lot of effort developing a bot, so I have a lot of thoughts on the game. This will hopefully be the first post of a series.
Personal History
I first discovered Hanabi while solving Board Games with Shrek in the 2020 Galactic Puzzle Hunt (in 2021). That summer, I played it with my brother and got a perfect score with some homemade strategies. 2-player Hanabi is quite different from 3+ players, but we felt that we had "beaten" the game at this point and didn't return to it.
In Feb 2022, the H-Group guide was discovered by some of my friends. I offered some of my thoughts on the game:
Oh, how I was mistaken.
In March, I played 4-player Hanabi with some high school friends, and the game felt significantly more difficult. We played with intuition again, but the difficulty sparked some new interest, and we delved into conventions and started playing Hanabi online.
In April, I reintroduced it to the group that found the H-Group Conventions, and it exploded. We played Hanabi multiple times a week and I fell in love with the complexity of the game.
Conventions in Hanabi
A convention is an agreement between players about a particular action that signals more information than is explicitly given. Conventions are common in bridge for partnerships to reveal extra information about their hand during the auction.
There's a surprising amount of controversy around conventions in this game. Lots of people call playing with conventions "cheating", "making the game too easy" and "taking the fun out of the game". They point to the rules saying that "you can only communicate with your teammates when you give them information", so adding extra information through conventions isn't allowed.
Unless you have a very lucky deck, there aren't enough clue tokens to get a perfect score with certainty. Eventually, you run out of clues and need to "guess" either a play or a discard with partial information. This is what most players learn when they play Hanabi for the first time. The game can't be solved just by giving information-efficient clues, but if you understand your teammate's state of mind when they perform actions, you can act on them without needing complete information. This can be formalized into a "convention".
A simple example of this: from the rules, players know that cluing 1 at the beginning of the game indicates that at least one 1 can be played. But using colour clues to prove that the other 1s are also safe to be played is very clue-intensive. Eventually, you realize that after being clued 1s, you can just play all of them and trust that your teammates will do something if you shouldn't (or wouldn't have clued 1 in the first place). Now a 1 clue can get multiple cards to play, instead of just one.
Some people get hung up on the explicit agreement of conventions. "If you naturally discover such guidelines, that's okay, but agreeing to them before the game starts is cheating." Maybe during the game you discover that one person is very aggressive and plays cards right away, while another is very risk-averse and tends to always give clues on their turn unless they have complete information. This is meta-information that is also not covered under the rules, but is generally considered okay to act on as well.
Personally, I find the game to be quite difficult and luck-based without conventions. Perhaps the game is fundamentally changed with their addition, but the new game has its own interesting decisions. I'd say it also depends on the set of conventions you're using. Even among players that play with conventions, a particularly strong convention set known as "hat-guessing" which involves modular arithmetic is typically frowned upon due to being "too strong" and reducing the game to just math.
I think hat-guessing can be fun in its own way: it reduces the game more to sort of a puzzle where you have to find a sequence of actions that can get a perfect score. Not all Hanabi decks can get a perfect score due to the end condition, and some decks can only reach a perfect score if the players distribute important cards evenly between everyone's hands. The stronger the convention set is, the more the game becomes an exercise to prepare for and react to bad decks.
Addendum
Part of the online discourse on Hanabi is also centered around the unfriendly nature of players on BoardGameArena. Players there are matched into games randomly based on their ELO. Without playing against the same people over and over again, it's impossible to understand what the intentions of their actions are. It seems like conventions that are widely agreed-upon would be a great solution, but new players don't know about them and maybe are in the camp that don't want to play with conventions.
I haven't played there myself personally, but I hear reports of players criticizing others for their actions after the game. Some players expect their conventions to be followed exactly and ridicule others for giving "useless" clues. Obviously, this turns off newcomers who might not even undrstand why such a convention exists. In fact, I feel the same way about playing games like Town of Salem online. If you don't know the "meta", you're immediately shamed, which has to be one of the worst new experiences you could possibly have for a game.
I play Hanabi on hanab.live, which has quite a different culture. Stay tuned for a second post.