Echo Chess: The Quest for Solvability | Hacker News Reader

Echo Chess: The Quest for Solvability

samiramly.com

128 pointsjxmorris12106 comments

Hey HN! I'm sami, the creator of echo chess. This is the true story of diving way too deep into a rabbit hole of chess, ML, and puzzle design. Hope you enjoy the read.

Originally built this chess variant as a fun hack but it really escalated since then. It's a single-player puzzle game. You're playing white, there's no opponent, and you need to clear the board to win. Every time you capture a piece, you become the 'echo' of that piece.

There's also an 'endless' mode with infinite levels generated in real time and validated by ML to ensure solvability. Took forever to make it work but it now has 99% accuracy. You can play the 'classic' mode here: https://echochess.com/ and endless here: https://echochess.com/?endless

Happy to answer any questions.

You're welcome here and it looks like a good submission and a great game! but this post also got a ton of bogus upvotes and quite a few bogus comments. Those things are quite against HN's rules - this is in both the site guidelines (https://news.ycombinator.com/newsguidelines.html) and FAQ (https://news.ycombinator.com/newsfaq.html), and we ban accounts that do it (I've banned 5 of them so far.)

Please make sure that you and/or your friends don't do this on HN in the future! The community here is hypervigilant about this kind of thing and will use unkind words like 'astroturfing' and 'spamming' and email us complaints when they see it.

Thank you so much for bringing this up! Still new to the community (long time lurker, first time commenter). I'm very thankful for your input and I'm glad you're enjoying the submission and the game :)

From my understanding, the earlier comments on this post were all existing players - but I may be mistaken. In any case, all duly noted for us new posters. Thank you for your help in keeping the HN community so awesome!

By the way, how does the software calculate solicited votes? Does it omit upvotes from a user on the same IP as the story creator?

Alas I can't answer that because it falls in the bucket of things that would stop working if they were public.

This is one of the (fortunately somewhat rare) cases where the principle of "optimize for curiosity" is at odds with itself!

https://hn.algolia.com/?dateRange=all&page=0&prefix=true&sor...

Sorry to hear that, but thanks anyway.

Are you aware of Solitaire Chess?

https://www.thinkfun.com/products/brain-fitness-solitaire-ch...

I was not! Just checked it out, great to see other chess variants out there. This looks like a simple but fun ‘clear the board’ puzzle. Here are the main differences with echo chess as far as I can tell:

1) No echoing mechanism. In echo chess, if you capture a pawn, you become that pawn. That means the maze effectively changes at every capture. The post linked above has a thorough analysis (and visual examples) of the strategic implications and limitations of this simple twist, so I highly recommend checking it out.

2)Forced to capture at every move. Solitaire chess seems to require a capture at every move. While that may appear to be a more difficult setting at first sight, it can actually lead to a much lower search space complexity by heavily restraining the degrees of freedom. In small enough puzzle boards, backtracking can become trivial.

3) No white pieces, so no squads, and no sacrifices. In echo chess, it’s white against the world. In future levels (starting 9), you get a squad of white pieces to use. This quickly becomes a double-edged sword: your ally is also a blocker on your quest. Higher levels even require you to sacrifice an ally piece in your squad to solve the maze. This adds a whole new level of strategy and complexity to the game.

4) Endless mode with ML. The ‘endless’ mode of echo chess continuously serves procedurally generated chess mazes in real time that are guaranteed to be solvable (with 99%+ accuracy) every time you solve a prior one. You carry over your white piece and ending square as a starting position for the next level. This adds a tremendous amount of replayability, variability, and continuity for the game. It essentially becomes a strategic Tetris variant.

There are lots of other differences and nuances but I really think the post linked above does a better job analyzing them. If you’re an experienced solitaire chess player, I’d love to hear your thoughts on echo chess once you try it out!

Thanks for sharing this cool variant too. I’ll make sure to give it a try :)

*oh and obviously echo chess has obstacles. The mazes would be significantly easier if you just removed every obstacle from the board, like Solitaire chess seems to do it

Hello and thank you for the neat article. I have not finished it yet (I'm still partway through the ML bit), so ignore me if this is explained somewhere, but as far as I can see you only considered "generate and test for solvability" approaches. But isn't there a direct way to generate puzzles by solving the board "backwards"? Start with a single white piece on the board. Then, pick a random predecessor of that state; either the piece moved there normally or it was a capture. In the first case just move the white piece back, in the second replace it with a matching black piece and place a new white piece in a spot that could have captured it. Do this a few times until you are satisfied with the number of black pieces.

The biggest issue I can see right now is matching up the starting piece with the previous puzzle's ending piece, but I feel that should be manageable with some heuristics and brute force. And one would have to test whether the puzzles generated like this are actually "random-looking" enough.

100% exactly. This is a very smart observation and is actually one of the main approaches I attempted first when tackling the creation of 'endless' mode. There are a few nuances and adjustments that would actually turn what you're suggesting into a somewhat viable approach, but I think in general you're on the right track with both the hypothesis and its limitations.

A lot of the early playtesting I did for 'endless' kept indicating, much to my initial dismay, that the continuity of the carryover white piece is pretty much essential. In hindsight, it kinda makes sense. Imagine playing Tetris or Temple Run but where every 30 sec you essentially start from scratch. I guess maybe that's why people are more likely to binge-watch a whole season of Breaking Bad back-to-back than a full season of Black Mirror?

If we didn't have that constraint for echo chess, we could've easily just saved the crowdsourced pre-labeled solvable levels into a big 'test bank' db, and randomly served one of them any time a player needs a new level to play. Think SAT/GRE questions that are all pre-curated beforehand but that get 'generated' at random for every participant.

Thankfully the ML classification approach I ended up going with completely sidesteps the carryover piece dilemma. It's like you said: you simply "generate [incl. carryover] and test for solvability". Plus it works, with 99%+ accuracy, and in real time. So I think we're good for a bit :)

you don't need to run the puzzle backwards to generate solvable positions, you run it forwards and generate the pieces from the solution moves.

Starting with the piece and square from the previous board, mark all squares but this one as unknown. Make a random move. Any unknown squares passed through get marked blank in the current board and in the puzzle. Randomly choose to keep the same piece (making this square blank in the puzzle) or switch (marking the chosen piece in the puzzle, but now blank in the current board). Continue making random moves (biasing slightly towards choosing unknown squares), eventually stop and randomly assign the remaining unknowns as obstactles or blanks. Because you've said you don't care if there's only one solution, this gives you solvable puzzles trivially.

This isn't a new idea, eg https://www.snellman.net/blog/archive/2019-05-14-procedural-... talks about generating solvable puzzles using the forward moves, you'd generally pair it with a filter that weeds out puzzles that are not fun for some reason (eg, solutions that random walk blank squares; these can be avoided at generation time by having a budget for move-to-blank)

That's a brilliantly simple approach. You could even have an estimated difficulty score that updates based on number of moves, switches, etc. and ramp up target difficulty as the random run progresses.

Yep. Even the boring, topology-agnostic 'macro' variables can be good proxies for difficulty: obstacles count, empty squares count, counts per piece type, etc. I don't have a direct source for this but the original echo chess post has a good EDA section (+ feature importance plots) covering the impact of such variables on solvability. At scale, average solvability of random levels might be a half-decent proxy for how the difficulty of individual ones would fluctuate.

It's weird that I almost immediately had the thought for essentially exactly the same approach while reading the article. Not that this reflects on OP; flashes of solutions like that I think are often mostly random.

But I wonder if this is a sign of things to come - rather than needing to find explicit deterministic solutions to many problems that might actually have one, because ML is getting much more powerful and accessible instead we'll just use ML models and get 99.9% accurate solutions, but say, well that's good enough.

> I wonder if this is a sign of things to come - rather than needing to find explicit deterministic solutions to many problems that might actually have one, because ML is getting much more powerful and accessible instead we'll just use ML models and get 99.9% accurate solutions, but say, well that's good enough.

You're not alone: http://www.incompleteideas.net/IncIdeas/BitterLesson.html

For a more echo chess specific answer, see my answer above to @bazzargh

Very valid take - few thoughts to share on this. And thanks for linking the writeup about Linjat's procedural generation. That was a great read. Many interesting insights on the approach the author used for finding solutions to the puzzles in his logic game. The solver method with its conceptual layers seems particularly interesting. I think the challenge with this type of 'forward' puzzle generation, however, is that it tends to lead to more trivial levels by default. The Linjat author actually admits this limitation in the same post, shortly after introducing the neat solver:

> "This process will not always produce a solution, but it's pretty fast (on the order of 50-100 microseconds) so it can just be repeated a bunch of times until it generates a level. Unfortunately it'll generally produce a mediocre puzzle. There are too many obvious moves right at the start, the board gets filled in very quickly and the solution tree is quite shallow."

This tracks well with my own earlier experiments and my intuition about the (in)consistency of generating interesting echo chess levels by solution-tracing one random walk at a time. That said, could this forward-pass procedural generation be improved upon by adding some discriminator/scoring system after it to make sure we're not falling for the most trivial of solutions? Absolutely. In fact, the author continues by explaining how Linjat does that as well.

> "The above process produced a mediocre puzzle. In the final stage, we use that level as a seed for an optimization process. The optimizer sets up a pool of up to 10 puzzle variants. The pool is initialized with the newly generated random puzzle. On each iteration, the optimizer selects one puzzle from the pool and mutates it. [...] We then run the solver in the special level-generation mode [...] to make it solvable again. After that, we run the solver again, this time in the normal mode. [...] The new puzzle is then added to the pool. If the pool ever contains more than 10 puzzles, the worst one is discarded. This process is repeated a number of times (anything from 10k to 50k iterations seemed to be fine). After that, the version of the puzzle with the highest score is saved into the puzzle's level database."

In other words, what we'd truly be doing is: (1) some iterative process to generate a (trivially) solvable walk, (2) add random mutations to make the (solvable) level interesting, (3) readjust to make the (interesting) solvable again, (4) rinse and repeat until we have a (hopefully) interesting and solvable level.

To be clear, there's nothing wrong with this approach - it could even give us more granular control of difficulty curving explicitly. Indeed, with the right tweaks, I bet some solid solver + optimizer process could be devised to generate non-trivially solvable echo chess levels starting from a forward random walk.

Philosophically, in fact, the last step of the Linjat optimizer sounds actually pretty similar to the way the current 'Endless' mode in echo chess selects a level to be served to the player. 50 random gens get evaluated by the ML ensemble, they get ranked by majority-voting of solvability first, and probability of being solvable second, and the level with the highest score is the one that gets committed to the game.

Granted, the current echo chess generator directly starts from a parametrized random pool of 'mutations' before running them through its solvability discriminator, as opposed to starting from a definitionally solvable forward walk kernel to be mutated. Mutations first, solvability second. But the result is the same. And given that the starting pool is parametrized, there is still ample control (implicitly at least) in adjusting the distribution of components like obstacles, piece types, topology, etc. to vary the expected difficulty of the seeds.

TL;DR: we can start from random weights or fine-tune promising ones. But we still need to do something to get non-trivial levels generated.

Fun write up and interesting game that repurposes known mechanics. I paused reading to solve your first fictional example and ended up using the exact strategy that you explain in the next few paragraphs. I don't play chess, but your write up and simple rules made the strategy part really intuitive (for the simple example). Excellent nerd sniping!

Yes! So happy to hear this. One thing I was really aiming for with the echo chess gameplay design is the ability for anyone to pick up the game without any prior familiarity with chess or other strategy games, while also offering a pretty exciting challenge for chess GMs and strategy veterans.

The fact that you directly got the solution to that fictional example kinda proves the point that 'type 2' folks (as described in that section of the post) can actually be at a disadvantage compared to the newcomers given their preexisting intuitions and heuristics. Curious to know if you ended up solving some of the main levels in 'classic' mode too.

> I paused reading to solve your first fictional example and ended up using the exact strategy that you explain in the next few paragraphs.

I did too, and really feel like it's the most natural strategy, even for regular chess players. I'm interested if OP has any anecdotal evidence that chess players would try to solve it by a "forward" algorithm rather than "backward." Even a natural chess player would get that this is a puzzle.

> anecdotal evidence that chess players would try to solve it by a "forward" algorithm rather than "backward"

I think the main point is less about the forward vs backward part, and more so about the assumed relative values of every piece, position, or configuration on the board. Anecdotally, playtesting did show that regular chess players tend to lean on preexisting heuristics that serve them really well in chess, but less so in echo chess.

Not sure how this data compares to other variants like Sovereign Chess. I bet there is a similar adjustment period required to unlearn some habits and learn new ones. Caveat to all this: after re-adjusting to the mechanics of a puzzle game and the specific implications entailed, I'm sure veteran strategy players would still outperform, on average. Even across broader genres like chess vs TBS vs 4X vs GS. There's likely some 'muscle memory' that the brain develops over time.

It would be great to include these links prominently in the article, fairly high up,

Great point, thanks. Will update.

I actually semi-appreciate being 'forced' to read through the great write-up.

Well done!

You, sir, are a gentleman and a scholar. Thank you for reviving the lost art of deep reading.

What a fun game and awesome write up! I've been considering building my own card game variation and this encouraged me to dive in and do it. I loved your balance of engineering/product/marketing/game theory throughout the article. Given the success, have you tried to monetize it at all?

Do it! If you build that game, I'd love to check it out. No plans for monetization. Just enjoying the quest atm. Glad you're enjoying it so far.

This was a lot of fun to read, really enjoyed the journey from game design to product design to ML. One thing I was hoping to ask was how come you felt the need to procedurally generate levels? I've often heard debates around whether content needs to be "hand-crafted" to be worth another human's time but curious to hear your take on this since it seems like you implemented both ends of the spectrum with endless and classic.

Also do you feel like you now have a general set of principles to procedurally generate levels that apply to games outside of echo chess? Puzzle games are great since they're well scoped for indie devs and I'd imagine a lot of would be puzzle designers would burn out before they create a few dozen-hundred levels.

> how come you felt the need to procedurally generate levels?

Three reasons: (1) demand for new levels was too high - game traction exceeded my laziness threshold as a designer; (2) puzzle lovers suffered from lack of replayability - game was effectively punishing core users who engage with it the most; (3) designing a 'good' difficulty curve required me to quantify a level's difficulty objectively - anytime I design a puzzle or strategy game, I also try to design an algorithm that can solve it to get a general sense of how the different levels compare in difficulty; (4) I tend to get obsessively curious about stuff - wasn't sure if it's feasible to have a 100% real-time procedural gen of chess mazes so I decided to do it to find out.

> I've often heard debates around whether content needs to be "hand-crafted" to be worth another human's time

LLM jokes aside, I think this is a great point and I'm not sure exactly what the right answer is here. I ended up keeping both Classic and Endless modes for this exact reason. If there's enough interest, I'll add a manual level generator for the community of 'humans' to submit their own hand-crafted creations for others to play.

> a general set of principles to procedurally generate levels that apply to games outside of echo chess?

Good question. I think it really comes down to this: (a) can you formalize the concept of a 'level' and its components for your game in a way as to encode/decode every game state (at a minimum) easily and efficiently? (b) can you parametrize this formalism in a way as to connect malleable randomizations to every meaningful component of a level to generate (hypothetical) infinite variability? (c) do you have a confident way to make sure whatever generation of a 'level' you're churning out is as playable, achievable, and as fun as the manually crafted one? The fun part is the hardest one to automate. That's where I think you need a very strong grasp of what actually make your puzzle game fun. All the rest can likely be generalizable to other games.

> puzzle designers would burn out before they create a few dozen-hundred levels

Tell me about it.

can you please implement click&click controls, like on lichess?

hold&drag is almost unusable on the phone

(and/or you need to resize the website, as it doesn't fit the screen neither in phone- nor in desktop-mode of the browser)

Click and click support is coming soon! Is the board itself not fitting on the screen? If you don't mind, can you please share what device/os/browser you're on. Resizing is disabled by default on mobile.

android, Opera

if I hold'n'drag up-down, it moves the viewpoint (together with the board)

might be because of URL bar appearing/hiding, never encountered this before...

edit: even with "toolbars - never hide", it still scrolls a tiny bit (tho the game becomes usable)

Hmm that's interesting. The screen is supposed to be non scrollable, non draggable and non zoomable on mobile to avoid this type of issues. Unfortunately it might be a bug for opera on android. I'll see what I can do. Just to make sure, this is happening in a fresh browser tab, not within a webview from another app - right? In the meantime, hopefully you'll able to play normally on other mobile or desktop browsers. Thanks for your patience and support!

> Just to make sure, this is happening in a fresh browser tab, not within a webview from another app - right?

yep

> Thanks for your patience and support!

thank _you_ for a great game

I implemented a partial generator based on the idea in my previous comment. It was quite a fun challenge.

At each step it determines the reachable squares for the given piece, that are not occupied or block past moves, and chooses one at random, then it computes the shortest path to that square. This procedure is repeated until there are no squares available.

Only pawns, knights and kings are supported so far.

https://gist.github.com/oessessnex/bc617095675da44f857216f98...

Great game btw :)

Glad you enjoyed the game - and the generator metagame. Thanks for pitching in and sharing your partial gen implementation!

> the reachable squares for the given piece, that are not occupied or block past moves

The last part is key. There's a similar discussion related to level generation here: https://news.ycombinator.com/item?id=37334186

If you do check it out, I'd be curious to hear your thoughts on the Linjat approach and the limitation around trivial solvability of gens without an optimizer step of some sort. Still unclear at this stage where the debate of ML vs deterministic solvers will land on this one, though there are already several insights discussed that can be meaningful for puzzle design in general.

Let me know if you end up expanding the code and/or going through the 'forward solver' tangent debate. Thankful for your efforts in taking a stab at this challenge!

I don't know if you still read this, but is there a chance to separate controls of sounds (piece selection, piece placement) and music (the score)?

I love the music, but a bit frustrated with the sounds

> I don’t know if you still read this

Certainly, feel free to drop a comment here any time.

> separate controls of sounds (piece selection, piece placement) and music (the score)

Not planned for the current minimalist version but I think that’s a good idea for a settings menu.

> I love the music, but a bit frustrated with the sounds

Sorry to hear that. Out of curiosity, is it the capturing sound in particular you’re referring to, or do you feel the same about the (less frequent) other SFX ones? Would be great to understand a bit more too what aspect in particular of these sounds you find suboptimal (genre, volume, frequency, specific audio, etc.)

> is it the capturing sound in particular you’re referring to, or do you feel the same about the (less frequent) other SFX ones?

Level end and level start are rare enough to not pay attention to, they're fine

Capturing the pieces is high enough note to not interfere with the music (and it sounds positive), but it gets boring(?) after a while

"Moving to an empty cell" on the other hand... I'd reserve it for errors, tbh. Something about that... sound of hitting a tin or glass, it feels unpleasant (and not neutral like simple maneuvering should be, imo)

Only now, after frantic replaying of sounds over and over, I understood that "wrong move" has different sfx from "move to an empty cell"... That's not obvious. | Also, I think that returning piece to its own place shouldn't sound like an error (especially since it is highlighted same green color as valid moves. I'd make this silent probably)

> Would be great to understand a bit more too what aspect in particular of these sounds you find suboptimal (genre, volume, frequency, specific audio, etc.)

Volume seem fine: my mouse is louder than sfx, but less loud than the song

And perhaps last nitpick, but does the song change bpm? I feel the urge to synchronize moves with the catchy beat, but I feel like I can't apply rhythm from the beginning of the song to its end (and vice versa)

Very helpful feedback. Thank you for that.

By the way, many have reached out asking about an echo chess community for future updates or feedback/discussions. I'm considering setting up a discord server for that.

Let me know if you're interested in future versions or levels of echo chess. I can add you to the early access list when the time comes.

Really odd to recognize we have a hard problem, but one that's very well specified & maps cleanly onto solvers (e.g. minizinc) and instead say this should be solved with a laundry list of sklearn.

This is one of the magical spaces where there is always a solution, the board space isn't that big & shrinks as you go

This actually isn't too hard to make a solver for. Especially in the single white piece case. I made a solver [0] that can solve level 8 (the hardest single white level) in less than 100 ms. I believe that it can solve every single white puzzle, but I haven't tested it thoroughly.

It works by reducing the state to currently alive pieces and the current white piece right after conversion. It computes the transversable squares and possible captures for each state and does a basic DFS. One neat trick I used is that for simple traversability, the queen and the king are the same piece.

Multiple white pieces makes the code significantly more complex, but it simply adds a little bit to the statespace.

[0]: https://github.com/TheThirdOne/assorted-examples/blob/master...

Nice work! I had a similar idea and also wrote a little solver in Rust [1]. I chose the same benchmark puzzle as is in your code, and it solves in ~25 microseconds on my laptop (i7-1165G7).

I haven't optimized my approach at all or even run it under a profiler, but it uses SIMD-within-a-register for computing the "flood fill" of which squares a piece can move to, which is a nice efficiency boost. For the simplest example, if you have a bit-vector `v: u64` of positions that a pawn might be in, then `v << 8` is the vector that denotes where it might be after one step, and `((v & can_move::LEFT) << 7) | ((v & can_move::RIGHT) << 9)` denotes what it might be able to capture.

I think the `Stepper` implementations and the way they flow into the top-level `captures` function is a cool and powerful approach; I encourage taking a look if it sounds interesting to you.

[1]: https://github.com/wchargin/echo-chess

Direct link to source:

https://github.com/wchargin/echo-chess/blob/main/src/main.rs

This is really neat. Thank you and @thethirdone for putting in the effort to tackle this! Love these creative takes to add efficiency boosts. You guys make HN awesome.

> Multiple white pieces makes the code significantly more complex, but it simply adds a little bit to the statespace.

That would be my guess too. Especially the sacrifice mechanic that needs to be timed just right after X moves/transformations of each white piece.

It's even simpler than that. You can randomly generate a valid sequence of moves (i.e you are a pawn at a2, move to a3, become knight, move to ..., move to ..., become ..., ...), instead of the initial board state and that guarantees the puzzle is solvable. The only thing you need to watch out for is that you are not allowed to touch squares that appear in previous moves.

This post has 5 astroturfed (flagged and dead) comments from accounts less than 2 hours older than this post all within 1 hour of this being posted, and all with only a single comment on their account. Hmmm...

Yes I got schooled by dang about this as a n00b in the community :') Long time lurker, first time commenter. See comment thread from dang above, he was super nice to explain to me all this stuff. Thank you all for being kind and welcoming.

Best post ever? The level of details is beautiful. Any plan in releasing an Android app? Thank you

Possibly soon. Should work fine on android mobile web in the meantime. Let me know if you run into any issues.

+1 for keeping the web version usable on mobile. I don't need something that runs in the background and tracks which IP addresses my phone passes through with a carbon copy to facebook via their sdk or whatnot.

Certainly. I'm always astonished how many games think turning into Cambridge Analytica is a prerequisite for doing basic ML on their own game-generated data.

A few comments on the game:

- would be good to support two tap moves like on lichens rather than only drag and drop

- drag and drop seems really buggy on my phone. Often had to repeat my move.

- accidentally clicked give up instead of try again, then my game was over? Not really sure why there is a give up button at all.

- the timer just adds stress instead of fun, for me.

- hated the music being on by default

- imho the obstacles should be symbols, not just a different square colour. I had trouble seeing them.

Great feedback, thanks for that! There's plans to support two taps soon. Same for an 'are you sure' button when giving up. The reason the button is there (aside from its psychological benefit to not give up in early playtesting) is that it allows players who get stumped at a certain level to save their high score to the leaderboard without finishing the game. As explained in the post linked above, puzzle games are, in some sense, different from arcade games in that you can never just die.

Which brings us to the next point: 'endless' mode handles the game over state with a countdown timer, ensuring a convergence toward an end game even in a (theoretically) infinite game mode. But that mode is purposefully designed to be more arcade-like and speedrunnable, versus 'classic' mode which is dedicated to strategic patient thinkers. If timing in games stresses you out, definitely feel free to stick to classic instead of endless mode. Many folks love the timing aspect, but if you've never been into things like blitz chess, it's totally understandable.

Thankfully, you'd be happy to hear that the scoring system is purposefully designed to minimize the impact of timing in classic mode for exactly that reason (check out the 'Scoring System' section in the post).

p.s. I'm surprised to hear drag and drop is giving you issues on your phone, sorry about that. Not sure any players have had that issue before. Do you mind sharing what device/os/browser you're using, and if you're accessing echochess.com in a fresh browser tab directly?

> it allows players who get stumped at a certain level to save their high score to the leaderboard without finishing the game

Have you considered saving the high score after every level automatically?

That approach could work too. There may be a few minor nuances here and there but it's workable. Each level currently does save the running score so far, and resets it to that value when the player restarts the level. It's just not saved as a high score on the overall leaderboard until the player actually ends the game session.

There's a section in the post about the ethos behind the scoring system and how it's designed to incentivize good gameplay while accommodating for speedrunners as a non-primary audience. It also ties in with the part about sawtooth difficulty curves and skipping levels. So some of these considerations can come into play here. In general I tried to reproduce the retro feel of arcade games without taking away from the strategy/puzzle solving kernel.

But yes, definitely. That's a valid approach too.

>As explained in the post linked above, puzzle games are, in some sense, different from arcade games in that you can never just die.

I didn't finish the post because it went straight into strategy tips before I had even had a chance to play!

Also personally I'm not really interested in arcade mechanics. I'm not interested in global leaderboards or whatever either. Just interested in playing puzzles in my own time on my own terms.

Your thing is very cool! I like the way it is so constrained it's often possible to plan 6-7 moves ahead without much effort.

>but if you've never been into things like blitz chess, it's totally understandable

I'm massively into blitz chess. But this is a puzzle thing, and for me, there is no need for a timer in a solo game.

> Do you mind sharing what device/os/browser you're using, and if you're accessing echochess.com in a fresh browser tab directly?

FF/Android. I didn't understand your second question.

Glad you're enjoying the puzzle exploration. Curious if you've tried levels 11+ btw? Planning 6-7 moves ahead gets trickier later on, especially when you reach the highest levels of 'Classic' mode.

I get your point about solo games vs blitz chess. Puzzle games aside, when I'm playing solo I tend to prefer Turn-Based Strategy games like HOMM, King's Bounty, Civ, Eador, AOW, etc. a little more than RTS games like SC2, Warcraft, AOE, BfME, DOTA, League, and so on. In multiplayer, RTS can be a lot of fun. Of course the best solo campaigns are always real gold, whether timed or not.

The nice thing about good strategy and puzzle games is that they can be enjoyed in different ways by all types of players who appreciate puzzle solving.

Currently stuck on level 10.

Btw it's a bit odd that there are no instructions anywhere on the site? I keep wondering if there's a rule I'm missing or something.

You have these rules in the blog post, but I find the language quite messy and imprecise:

> You are playing White, there is no opponent. You must capture all pieces to win.

> You become the "echo" of any piece you capture. Captured a bishop? Become that bishop.

> You can’t pass through red obstacles. Find the best move order to clear the board.

For starters, "you" is used to describe both the player and the piece. And the last rule contains two different statements, the second of which is redundant from the first rule. It also doesn't mention that there can be more than one white piece, or that white pieces can capture other white pieces.

Maybe something like:

1. The goal is to capture all the black pieces, which never move.

2. Move one white piece each turn, using the basic rules of chess piece movement. You can't move through red obstacles. Pawns don't promote.

3. When you capture a black piece, your white piece turns into the type of piece you just captured.

> I'm playing solo I tend to prefer Turn-Based Strategy games like HOMM, King's Bounty, Civ, Eador, AOW, etc. a little more than RTS games like SC2, Warcraft, AOE, BfME, DOTA, League, and so on. In multiplayer, RTS can be a lot of fun

For some reason, I'm the opposite - I hate RTS against humans.

Nice. That's a good way to rephrase the rules. Only thing to note is this part:

> When you capture a black piece, your white piece turns into the type of piece you just captured.

The echoing mechanism actually applies to any captured piece. You'll see this mechanic in action starting 12+. By "you'll see", I mean the game progression and level design will purposefully force you into following a path which illustrates the new mechanic that needs to be learned. The lack of explicit text instructions, tutorials or handholding in is a feature of echo chess, not a bug. See the 'difficulty curves' section of the post.

> Currently stuck on level 10.

Yes, this is one of those levels that feel incredibly frustrating until it just 'clicks'. In my playtesting experiments, users either smile/laugh audibly when they finally get the solution to level 10, or they let out a big sigh of relief. Let us know how it goes :)

>he lack of explicit text instructions...is a feature of echo chess, not a bug.

Personally, I don't care for it. To me the essence of a puzzle is a clear goal, and a clear set of constraints, within which you try to find a solution. If there are unspecified means available, it's something different, like a "a puzzle with a trick to it". Like one of those lateral thinking problems where it turns out you're meant to fold the paper or something, because they never said you couldn't.

It's easier to enjoy and get deeply into a puzzle when you know for sure it's solvable with the information you have.

>Yes, this is one of those levels that feel incredibly frustrating until it just 'clicks'. In my playtesting experiments, users either smile/laugh audibly when they finally get the solution to level 10, or they let out a big sigh of relief. Let us know how it goes :)

I got it just after posting. I had just missed one of the possible pathways for a knight to get to a certain square. Was going through the process of proving that the puzzle was impossible - often a good way to solve. :)

> I got it just after posting. I had just missed one of the possible pathways for a knight to get to a certain square. Was going through the process of proving that the puzzle was impossible

Nice :) That's the way to do it. I think you'll really like 11+.

Somehow I found 11 easier than 10. But then, it also felt a bit guessier - harder to systematically try each path.

Interesting. I think that's tied to the degrees of freedom linked to bigger boards with fewer obstacles. Coincidentally, the EDA section of the post finds similar indications for the 1,000s of procedurally generated levels segmented by board size and obstacles ratio.

Similar to them, I also noticed some weird issues on iOS where it would sometimes drag the page when moving pieces and, other times, prevent seeing either the top or bottom portion of the UI. I ended up moving to PC for that reason. I also recall not being able to type in a name for the score at the end (on iOS).

One other thing I noticed was that submitting a lower score (at least in endless) still overrides your old one. (My scores went 860.5k -> 314.7k -> 446.9k -> 136.7m, overriding every time.)

Question: when you say iOS, do you mean navigating to echochess.com directly on a new window in a browser like safari? The only time I've seen that weird behavior you're describing is when a webview is being loaded for the game from within some other app. The second part sounds like a bug - thanks for the heads-up!

I'm still not over how you casually dropped that you reached 136.7 MILLION btw. gg.

Both. I don't recall if this is necessary to cause it to start happening, but as soon as you pinch any amount with two fingers for zooming in/out (or to scroll down to see the rest of the cut off UI), the behavior sticks around for a while.

I'm not entirely convinced that this is anything on your end, as I have run into similar issues with my sites, and all the "answers" online don't really fix it. I believe the only real solution is some combination of setting viewport, disabling certain scrolling/finger gestures*, and ensuring that the content on screen doesn't go off the page. I'm no expert though.

*: I don't recall this being absolutely necessary, and it is generally not recommended for accessibility reasons. I believe that I mostly fixed it with just setting the proper viewport meta tag and ensuring content doesn't go off the screen.

Interesting. I'll look into it. Thanks for letting me know and for sharing what worked for you before.

what's wrong with music on by default?

flash games operated like that from the beginning till the end

I guess it's normal in the arcade world, but not in the puzzle world.

Actually most well-reviewed puzzle games on Steam and mobile do come with some killer background tracks. The echo chess track has been surprisingly popular - anecdotally, one of the early playtesters mentioned they routinely run echo chess in a background tab while working to get into deep focus mode. Granted, the board game version of the puzzle word does music differently for obvious reasons.

Just like you, I accidentally hit "give up" at one point by mistake. I actually found the music quite good.

In a somewhat similar vein, I found the endless mode to be a bit tiring, since you have to keep up the pace to maintain enough time. It could be nice to have a pause button for endless mode (or both modes). Of course, it would defeat the purpose if someone could just pause right after seeing each board, but I feel like having a pause button with some sort of multi-minute cooldown could be an interesting addition. For some people, this might defeat the purpose of endless mode, but it's just a thought!

I also ended up playing endless long enough to get a score that was too large; my score overlapped with my name on the leaderboard. (I reached level 157 with 136.7m score, then I let time run out due to my hands getting tired.)

> I actually found the music quite good.

I'm not expressing an opinion on whether the music is good or not. I just really don't want (or expect) any music to play. It's particularly annoying when I play on my phone in a quiet moment, and suddenly music is blasting out. It doesn't seem to remember the setting.

That's fair.

Side note, unrelated to echo chess - which of these (very eclectic) TBS or puzzle games would you say have soundtracks that are more of a fit for the solo puzzle-solving experience you'd find ideal: Tetris (tanaka), HOMM (romero), Civ (knorr), or small indies like Monument Valley, Into the Breach, etc.?

Silence would be my preference, honestly. Then I can listen to my own music if I want.

Lightweight puzzles are likely to be something I do while doing something else. It's pretty presumptuous for a puzzle to think that there is no other music that it could conflict with.

Interesting perspective. Most people I know who are into strategy games listen to their favorite OSTs in their daily life. Personally, my Spotify playlists are mostly filled with composers like Paul Romero. There’s nothing like a good track to set the ‘right’ ambience (if there is such a thing) envisioned for an audience.

I agree that music is a super personal thing, though - in games or beyond. That mute button in echo chess is as old as the first SFX audio file I playtested. Point taken on its default state and persistence. Thanks for sharing your candid thoughts throughout.

I wouldn't say I'm all that into strategy games. I find them a bit addictive so tend to avoid them. I did play a bit of Grand Ages: Rome recently. The music was ok, but it obviously gets repetitive.

I have tried the thing you mention and listened to computer game music in other contexts, but really, it's not my thing. I'd rather listen to classical, or jazz, or pop, or...almost anything.

Understandable take. I also recognize that “strategy games” is such a broad umbrella term. Back in the OG board game era (pre-neo-renaissance of tabletop gaming these past pandemic years), we had abstract grand strategy like Risk, old-school tactical wargames, and crossword-type or rush-hour-like puzzle games. Nowadays, if you take MOBAs, TBS, RTS, 4X, GS, or even any TRPG or RTT, odds are it can viably be categorized as a “strategy” game to some extent or another.

Even the new strategy board game and analogue CCG scene is so stratified these days. Which one of these games would count as the “true” archetype of a strategy game: Mage Knight, Terraforming Mars, Agricola, Sovereign Chess, Dune Imperium, Gloomhaven, Azul, Catan, Theomachy, or MTG? They each seem to have increasingly more “strategic flavor” differences separating them from each other than similarities. Same goes for table-top RPGs of the 2020s.

All this is to say, if the strategy genre itself can’t be painted with the same brush, then it sure can’t be optimally paired with the same universal type of music.

No, but I would distinguish between immersive games that expect to be run full screen, with your full attention and casual games that you might flip back and forth between. It's much more forgiveable for the former to play music at you, I think.

You make me realise I'm not sure what makes a game "strategy" per se. Games like Agricola don't feel very strategic to me, in that there is not much scope for long term planning, or predicting what other players will do. Instead, you just react to the situation in front of you, trying to make the most +EV play.

> You make me realise I'm not sure what makes a game "strategy" per se.

The business world can’t even agree on this one. There are maybe as many HBR rants swearing by Michael Porter’s definition as there are indignant talking heads criticizing it. Same for all the flavors of Nash economics or ESS in biology.

For a game to be ‘strategy’, I’d say some element of deductive reasoning or foreplanning being a prerequisite for (better odds of) success is necessary, but not sufficient. A min decision space complexity that makes the former non-trivial is likely sufficient.

Some might argue that decision making under uncertainty, or some version of stochastic optimization is necessary too. Or that strategy (as opposed to logic) is only relevant when more than one agent is decisioning at some level - making a clearer distinction with puzzle solving, PvE, emergent gameplay or meta strategy. Are they right? Maybe. Does it make any difference beyond gatekeeping? Probably not. Some of the best designers I know purposefully blur the lines between established genres when creating their games.

> Games like Agricola don't feel very strategic to me, in that there is not much scope for long term planning, or predicting what other players will do.

BGG often has heated debates on this point. I think it’s mostly a eurogame vs american-style thing (I’m a fan of both camps for different reasons).

Your outrageous high score is breaking the endless leaderboard UI! Well done :)

I get your point about the pausing concern. I've actually thought about that in past playtests and I think the long-term solution for these things is likely even more drastic: increasing the difficulty of the procedural gens incrementally more after X levels have passed. And/or capping the winnable time back from solving every consecutive level after the first Y. There are lots of interesting things that can be explored in this area - see the last section of the original echo chess writeup.

Awesome to hear you reached LEVEL 157 in one run! Curious if you got taken by the 'one more turn syndrome' [0] in that session, or if you had embarked on this run with a clear goal of surpassing 100,000,000?

And please make sure to ice those fingers. echo chess cannot be held liable for finger damage.

[0]: https://en.wikipedia.org/wiki/Civilization_(series)

Increasing the difficulty over time sounds fun! As an idea, there could also be multiple endless modes which either have faster/slower ramp-ups, start "further into" the difficulty, or just have fixed "easy," "medium," "hard," and "ramp-up" (curve).

To be honest, at first, it was less of an urge to get "one more turn" in and more of an urge to make sure I had beat my original high score. Once I surpassed it, I was trying to see how long I could survive without running out of time. It was at that point where I realized I could keep going forever without running out of time (I could recoup more time than I spent, and I would regularly hit 99 capped time). After this revelation, I set a goal of going until my hands got tired. Once my hands got tired, I almost succumbed to the "one more turn syndrome," but after moving (I believe) one piece, my score had a nice 3-digit repeating pattern and was a round number, so I called it quits.

Luckily(?), my hands have made it through games that are far more torturous on the fingers (though it has been a while).

This reads like the incident history chart of a new patient of hand therapy. Love it.

Sami is brilliant. He demoed Echo Chess at a recent San Diego engineer event and everyone was blown away and asking tons of questions. A lot of love and intelligence went into building this game.

thank you for the support, glad you're enjoying echo chess. it's been a ton of fun building a chess variant with ML. happy to answer any questions.

aside: i always hear about cool events like this after the fact.

i have tried to find sites that have listings of hacker/engineering/conference type events, but most of them are very spammy, or low signal. is there a good resource for finding these?

Yeah, you're right it can be tough. We started our own organization (https://sdx.community) centered around hackers/builders because it felt like it was missing, exactly as you described!

We share on Twitter, Luma, LinkedIn, and try to get other community groups to amplify, but there's a lot of noise out there, so we likely miss a lot of cool people.

Sometimes you get lucky and there's a good community slack/discord (for example the San Diego Startups slack) where you'll see most events posted. Otherwise, startups that are hiring engineers tend to sponsor and share events. Beyond that you have to just find out from other hackers where they're speaking or joining something.

Where do you live?

quite a drive from San Diego, i'm afraid, but I'd love to make a trip of it if non-natives are welcome!

Got addicted to this game over the summer. Fun twist on chess puzzles and the upper levels get increasingly sophisticated. I think I got stuck on Level 13.

Glad you're enjoying it. Making it to Level 13 is pretty awesome. I remember one of the early playtesters calling it 'the level from hell'.

Are you sure that level 13 is possible?

There doesn't seem to be a way to both take the f2 king and the a1 pawn. The b6 bishop can't reach either. The d1 pawn can only reach one or the other.

Absolutely :) It has more than one solution, with the optimal one using 35 moves. Have you tried solving level 12 first? The 'aha' moments in echo chess build up on each other one level at a time.

I have! It was a light and fun level. c:

Perfect. So the same mechanic learned in 12 can be leveraged in 13+. Obviously here timing is everything. I think 13 is a good example of a level where 'forward' or 'backward' passing alone won't be enough. It's almost like the best strategy to solve these mazes is 'middle out' (not to be confused with the infamous algorithm by Richard Hendricks).

Spoilers: Work your way to the a1 pawn, then a2 king can take the f2 king.

#nospoilers :')

I had that idea, but even with that, I'm still stuck. I get to a position with white king stuck behind the pawn on c3, with black pieces on a5, a6 and d6.

Or I start with dxe, take the white rook with the pawn, and end up with black pawn on a1 and white bishop on e6.

Another hint?

EDIT Oh never mind, finally got there. Just a slight tweak to the move order, which took forever to discover.

Most of the pictures are not displayed. (This seems to be because they are WebP format even though the file name is ".png".)

Do you have a full description of the rules, and do you have the FEN? I like to know the rules if I want to play game, and, it is not working so I made up my own, and if the levels is available then I can play game.

The below is I made up my own (I don't even know, if it is the real rules or not; but it is what I had understood):

  ; Echo Chess
  
  (InputXY)
  
  (Control
    Input
    (INIT $Cursor 1 1 0 0 Create =@cur)
    (KEY IgnoreKey)
  )
  
  ($Cursor
    (Image "Cursor0" "Cursor1")
    (DefaultImage ())
    (Density -10)
    (CREATE LOOP 0 1 50 Animate)
  )
  
  ($Tile
    (Image "Tile0" "Tile1")
    (Density 10)
    (INIT Loc + 1 band =Image)
    (CLICK @cur ,ObjBelow #Move Loc ,Send . 1)
  )
  
  ($White
    (Image "P" "N" "B" "R" "Q" "K")
    (CLICK @cur Loc ,MoveTo)
    (#Move
      fork
        Image (case
          (0 :pawn)
          (1 :knight)
          (2 :bishop)
          (3 :rook)
          (4 :queen)
          (5 :king)
        )
      then
      if
        Arg1 Arg2 MoveTo .
        Arg3 if
          From ,Image =Image
          From ,Destroy .
          (=P $Black) lnot if WinLevel then
        then
        @cur Loc ,MoveTo .
      then
    )
    (:pawn Yloc Arg2 1 + eq Xloc Arg1 Delta Arg3 eq land)
    (:knight Xloc Arg1 Delta dup * Yloc Arg2 Delta dup * + 5 eq)
    (:bishop Xloc Arg1 Delta Yloc Arg2 Delta eq if =:queen else 0 then)
    (:rook Xloc Arg1 Delta Yloc Arg2 Delta land if 0 else =:queen then)
    (:queen From Seek =%d Loc begin %d NewXY over over ObjTopAt dup From eq if . . ret then ,Class $Tile ne until . . 0)
    (:king From Chebyshev 1 eq)
  )
  
  ($Black
    (Image "PB" "NB" "BB" "RB" "QB" "KB")
    (CLICK @cur ,ObjBelow #Move Loc 1 ,SendEx . 1)
  )

Are you referring to the images in the post or the actual game? Looks good on my side, might be the unexpected extra traffic. Sorry about that! In any case, you can try the game directly here: https://echochess.com/

The rules are really simple:

1) You are playing White, there's no opponent. You must capture all pieces to win.

2) You become the "echo" of any piece you capture. Captured a bishop? Become that bishop.

3) You can’t pass through red obstacles. Find the best move order to clear the board.

You can play it on any device, just drag and drop the white piece to move around. Let me know if you have any issues.

p.s. love that you just made your own!

I can't "play it on any device". It doesn't work on my computer. (It is why I asked if there is some way to access the FEN, in case of it won't work and you want to play game on another computer, or by actual chess pieces on a board instead of on the computer, etc)

I read the rules like you wrote it here too, it is same thing, and I understand that. Nevertheless, it does not answer all of the questions (e.g. pawns promotion). From the example, it seems to not be check/mate, but I that short explanation won't explain everything. Capture all pieces? Do you mean capture the black pieces only? You cannot capture the white pieces, isn't it (otherwise there won't be any to capture it)? Is the code I wrote, the correct rules of the game?

Yes, I found those rules unclear.

My version:

1. The goal is to capture all the black pieces, which never move.

2. Move one white piece each turn, using the basic rules of chess piece movement. You can't move through red obstacles. Pawns don't promote. There is no check.

3. When you capture a piece (black or white), your white piece turns into the type of piece you just captured.

Yes, that is much better.

Then, the code that I wrote is OK (I think) except I did not implement capturing white pieces (although if white pieces can capture white pieces and change into the same piece, then effectively the white piece can become vacant if it can reach another white piece).

Here is the updated code. Push D to destroy the selected white piece (if it meets the criteria for being destroyed).

  ; Echo Chess
  
  (InputXY)
  
  (Control
    (INIT $Cursor 1 1 0 0 Create =@cur)
  )
  
  ($Cursor
    Player
    (Image "Cursor0" "Cursor1")
    (DefaultImage ())
    (Density -10)
    (CREATE LOOP 0 1 50 Animate)
  )
  
  ($Tile
    (Image "Tile0" "Tile1")
    (Density 10)
    (INIT Loc + 1 band =Image)
    (CLICK @cur ,ObjBelow #Move Loc ,Send . 1)
  )
  
  ($White
    Input
    (Image "P" "N" "B" "R" "Q" "K")
    (CLICK @cur Loc ,MoveTo)
    (#Move
      ,:movable
      if
        Arg1 Arg2 MoveTo .
        Arg3 if
          From ,Image =Image
          From ,Destroy .
          (=P $Black) lnot if WinLevel then
        then
        @cur Loc ,MoveTo .
      then
    )
    (:movable
      Image (case
        (0 :pawn)
        (1 :knight)
        (2 :bishop)
        (3 :rook)
        (4 :queen)
        (5 :king)
      )
    )
    (:pawn Yloc Arg2 1 + eq Xloc Arg1 Delta Arg3 eq land)
    (:knight Xloc Arg1 Delta dup * Yloc Arg2 Delta dup * + 5 eq)
    (:bishop Xloc Arg1 Delta Yloc Arg2 Delta eq if =:queen else 0 then)
    (:rook Xloc Arg1 Delta Yloc Arg2 Delta land if 0 else =:queen then)
    (:queen From Seek =%d Loc begin %d NewXY over over ObjTopAt dup From eq if . . ret then ,Class $Tile ne until . . 0)
    (:king From Chebyshev 1 eq)
    (#Destroy
      From Self ne if
        From #Move Loc 1 ,SendEx .
      then
      Destroyed lnot
    )
    ('D
      @cur Coloc if
        $White #Destroy Loc BroadcastAnd .
      then
    )
  )
  
  ($Black
    (Image "PB" "NB" "BB" "RB" "QB" "KB")
    (CLICK @cur ,ObjBelow #Move Loc 1 ,SendEx . 1)
  )

It is also possible to add more pieces e.g. Chinese cannon, or other kind of changes if desired.

Love this game!!

Glad you're enjoying it. What level did you reach?

This could be a good coffee table book.

Down to make a coffee table version if you know a good print shop. Can send you a copy for free.

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