Putting the simulator on the shelf – for now

Though I haven’t made any updates to Deck Simulator for Hearthstone in several months, I’ve decided a bit more formally that I am going to stop development for the time being.

As my first app on the Apple mobile app store, it’s been a great experience and I’ve learned so much. In around nine months I’ve managed to get over 600 downloads, and though that number may seem small I accept it as an honor, and want to think every single person who downloaded and used this app.

There are several reasons I’ve decided to halt development, one of the main ones being I stopped playing Hearthstone. I still believe it’s a great game, and with the recent introduction of the iPhone client I think Hearthstone’s golden age has yet to come.

For those who have used the app recently you probably realized that some cards were missing. Though I have done my best to integrate almost all of the cards from the original sets, the process of adding new cards is unfortunately very tedious and time consuming. It involves manually inputing the card information, modifying the engine where new gameplay mechanics are introduced, modifying the AI to properly accommodate the new elements, and then running extensive tests to see the cards are working and being played in a reasonable way by the AI. Of course with a pretty complex codebase new bugs crop up which need to be fixed before release. I had a great time doing this for the first few hundreds cards, but the magic wore off.

And to be honest, the relative lack of downloads was a factor, although given the plain visual design, awkward visual interface, and missing cards, I’m not surprised by the lack of popularity.

Nonetheless, I am not promising to never work on the project again. If somehow the Hearthstone bug bites me again, I may very well go back to updating things. If you want the project to be continued (by me or someone else), please like this article to show your support. Of course comments on this blog, or reviews on the app store are much appreciated.

Alternatively, if anyone is interesting in purchasing the source code please free to contact me (Email: decksimforhs at gmail.com). I am a supporter of open source but the only reason I hesitate to give it away is the amount of time spent in it, and (what I feel) is potential to make money.

If you’re reading this and were considering downloading the simulator, go ahead and try it. For all the missing cards I still feel there are a wealth of experiments you can perform to help your gameplay, especially for beginning or moderate players. And I don’t know any other tool that provides all the same features, especially the one which rates relative card value.

I started this project with the idea “Hey, wouldn’t making a hearthstone simulator be cool?”, and in that sense it was a major success, without a doubt.

As for a final reason I decided to halt HSSIM, I have decided on trying to develop my own games for iOS. You can see my latest game here (a puzzle game influenced by games such as Go and Othello):


The game’s blog is here, and I am also planning to write about mobile game development in general.


Deck Simulator for Hearthstone Version 1.4 Released! (added all Rogue cards)

Version 1.4 of Deck Simulator for Hearthstone has been released on the Apple app store as a free iPad app.

The main highlight of this version is the addition of all Rogue cards (minions, weapons, and spells), and also the remainder of the Pirate-themed cards, bringing the total number of cards in the database over 400. I’ve added four new decks, three Rogue and one Warrior pirate deck.

Pirate cards (full list here) are one thing I was always curious about in Hearthstone. I didn’t want to spend my precious dust crafting these cards but I wondered how strong of a deck could be made which contained all of them. Though not entirely conclusive, using the simulator I got a strong indication that pirate decks really aren’t that strong (which was in line with my feelings on the matter). However if you know of a Pirate-themed deck that you think is especially good, let me know and I’ll test it out in the simulator and let you know how it performs.

One reason I had been hesitating about adding Rogue cards is because several of them contain a completely unique strategic element, “combo”, which is not used by any other class. Modifying the engine to handle the rules related to combo wasn’t too hard, but I had to do some tweaking of the AI engines to make them play Rogue decks with reasonably strong strategy.

In this release I also added the ability to copy the simulation log. This allows you to save the results of lengthy simulations you ran for later reference, or to save particularly interesting game logs for later. The logs are simple text so you can paste their contents into emails, blog posts, or anywhere else that accepts text. I hope to be showcasing how the AI works in future posts with the help of such logs.




Detailed card statistics in the deck simulator

In addition to the 50-some cards I added to version 1.3 of Deck Simulator for Hearthstone, I also included a new feature where detailed statistics are tracked for each card and displayed in the “Game log” window at the end of the simulation, organized by deck.

I’ll give a few examples to explain what these statistics mean and how to interpret them:

  •  (Fireball): draw = 72%, play = 54%, att =  0%, died =  0%, dam = 3.268232

I think most of you already know “Fireball”, but just in case it’s a neutral spell that deals 6 damage to any minion or player for a cost of 4.

“draw” here represents the percentage of games in which a Fireball card was drawn. This includes even if the card is redrawn initially, or if the card is drawn and not used. Generally speaking, this number is a function of the number of the card in the deck (either 1 or 2) and how long the average game lasts. It doesn’t mean too much on its own, but is useful when combined with the other stats.

“play” here represents the percentage of games in which Fireball is played (cast). It must be less than or equal to the “draw” figure, since you can’t typically play a card without drawing it (except for a few special cases). If this figure is much lower than “draw”, then that usually means there wasn’t frequently enough mana to play the card or a good opportunity to play it.

“att”, “died” represent the number of times this card attacked or died in a game. It only applies for minions and is therefore 0% for spells like Fireball. “att” can be higher than “play” since a minion can attack several times a game if it stays alive or has windfury.

“dam” represents the total amount of damage this card dealt on average in all simulated games in the current run. For cards like spells you can sometimes figure this out from the other statistics (i.e. for this card we see that 6 x 0.54 = ~3.2), but for minions this number is a bit tricker since it includes damage both from battlecries, deathrattles, as well as attacking.

  • (Ragnaros the Firelord): draw = 71%, play = 52%, att =  0%, died = 21%, dam = 7.480020

Ragnaros, one of my most favorite cards, is a unique case since it is a minion but can’t attack, and so “att” statistic is 0%. However, since it does deal 8 damage at the end of your turn, the “dam” statistic is non-zero (around 7.5).

If you think about these statistics can you can draw some conclusions. For example, Ragnaros deals 8 at the end of each turn, yet it dealt around 7.5 on average. Putting this together with the fact that it was only played around half of games (52%), this implies that it dealt damage roughly twice per game, and was alive about two turns.

However, since it only died less than half of the time it was played (21% vs 52%), why didn’t it typically live more than two turns? Easy – this means that the game tended to end around two or three turns after Ragnaros was played, and I’m betting it was often in favor of the player who managed to play this great card.

  • (Elven Archer): draw = 64%, play = 63%, att = 38%, died = 58%, dam = 1.183317

In the case of Ragnaros, the card was played roughly 73% of the time (= 52%/71%) it was drawn, which is actually pretty high considering it costs 8. But if you look at Elven Archer (1 1/1 for cost of 1 with 1 damage during battlecry), it was played roughly 98% (= 63%/64%) of the time. This makes sense because it’s cost is so low.

With only a one in toughness, it died most of the time (58% / 64% = 90%) and only managed to deal 1.18 damage per game. This translates to 1.18 / 63% = 1.873 damage when it was played, and 1.0 of that is from the battlecry. However you shouldn’t jump to conclusions that this card was useless since it did so little damage-wise, because that would discount the preventative effect it might be having to kill enemy attackers or other minions that are part of dangerous combos.

You may be wondering why the draw rate is not higher than Ragnaros, the reason is because I have only one of this card in the deck (same as Ragnaros).


These stats take some time to understand but I’m hoping many people will find them useful or at least interesting. For starters you can use the damage stat to see which cards are pulling their own weight and which are slacking, and tweak your deck to improve your overall win rate. And if you get creative, the sky is the limit!

Deck Simulator for Hearthstone 1.3 released (more cards)!

I’m very pleased to announce that version 1.3 of Deck Simulator for Hearthstone iPad app has been released on the Apple App store.

Since I’ve released this app I’ve gotten feedback from several people that there needs to be more cards added to fill out the entire set of Hearthstone cards. Adding cards is a time consuming process but I decided to focus on this for this release. I’ve added all Shaman-class cards as well as all Naxxramas cards, around ~50 new cards for a total of 366 in the database.  Though there are still some cards missing, this brings the percentage of total cards much higher and should make it a much more productive tool.

The Naxxramas cards are especially important since they can involve a lot of work to get hold in the actual game. With this app,  you can play around with the cards you haven’t had a chance to acquire yet.

Besides the new cards I’ve also fixed a bug which made the Planner AI weak in certain cases, and also added card level statistics which appear at the end of each simulation and give important information such as average amount of damage dealt by each card. I’ll write up on a post on this feature soon.

Here is the app’s page on iTunes:


You can also search for it in the app store with the keywords “Hearthstone Deck Simulator”  (without quotes).

Card Importance Testing in the simulator

This is the third installment in a series of three posts about the new features present in 1.2 which has recently become available on the app store.

The first two discussed the per-participant statistics and HELO (Hearthstone ELO), and this final post will focus on Card Importance Testing which is another new feature.

One of my goals in writing Deck Simulator for Hearthstone was to create a tool which would allow adjustment of existing decks to improve their overall effectiveness, or simply put, win rate. While it is possible to create a bunch of variations of a deck with different card variations and test them, doing so can be time consuming and tedious. Because of this, I decided to try and add a feature which would help guide how to modify a deck.

Because of the large number of cards available (a few hundred including neutral cards), rather than focusing on what card(s) to add, I decided to focus on determining which cards to remove. After all, since all legal decks in Hearthstone require 30 cards, if you want to add a card you must first remove one. (Note: Below you will see a reference to using a  28- or 29-card deck, which is a special feature only present in the simulator)

Imagine you knew which of your cards really were doing the lions share (helping win games) and which were just going along for the ride. This would be one major step to finding how to improve your deck, since you could replace those cards with other cards that might have a greater positive effect on the deck as a whole.

I’ve added this type of Card Importance testing via a single button available on the “Configure Simulation” screen, aptly titled “Test Card Importance”. To use this, simply choose a AI Player and Deck, and click the button. This will add several participants (AI + deck combinations) to the list of participants:

  • Two participants where the selected deck is added, unchanged.
  • One participant with a modified deck where all cards of a certain name are removed from the deck. This can be one or two cards depending on how many were in the deck, and these holes will not be filled with other cards. For example if your deck contains two instance of “Arcane Missles”, there will be one participant with both of these cards removed (down to a 28 card deck), and whose name will be of the form :(removed XXX) > original deck name (due to space considerations the player being used will not be shown in the name as it usually is).

The reason for the first unchanged deck is so you can play each deck missing one of the card names against the unchanged deck, and compare to see whether the removal of thiscard decreased or increased the overall win rate. Alternatively, if you want to compare against another deck you can add that deck first before clicking the “Test Card Importance” button, and all modified decks will play against that instead.

(The reason for the second unchanged deck is to help guide the right number of games per match. More on that below.)

To illustrate a real example, I did the following:

  • Selected “Evl. AI (strong)” as the AI Player (or just leave it as this is the default)
  • Selected the deck “Evolved Paladin 215” and clicked “Add to simulation”
  • Selected the deck “J’s Mage Deck” and clicked “Test Card Importance” (blue button on right middle)
  • Made sure Simulation Type was set to “All play first”
  • Changed the slider “Matches per pairing” to 1001 (maximum value)
  • Clicked “Start simulation”

Here is an excerpt from the results I got:

  • [1921] Evl AI (strong) < Evolved Paladin 215 < Win 80.9% of 23023>
  • [1121] (removed ‘Arcane Explosion’) > J’s Mage Deck <Win 24.2% of 1001>
  •  …
  • [1062] (Unchanged) > J’s Mage Deck <Win 19.4% of 1001>
  • [1018] (Unchanged) > J’s Mage Deck <Win 19.3% of 1001>
  •  …
  • [883] (removed ‘Ragnaros the Firelord’) > J’s Mage Deck <Win 15.4% of 1001>

The most important thing to know about reading these results is that they are backward from what you might usually expect. For example the fact Ragnaros is on the bottom of the results (with a 15.4% win rate versus an 19.3-4% one for the unchanged decks) actually means Ragnaros is one of the main contributors to this deck since without him it’s performance falls significantly. Conversely, the deck actually performed *better* with two Arcane explosions removed from the deck.

So, from this little experiment we learned some information about one card that we probably wouldn’t want to remove from the deck (Ragnaros) and one that is a good candidate for swapping out for something else (Arcane Explosion).

The reason for the two unchanged decks is to determine how stable the simulation results are based on the number of matches per pairing. Ideally, since these decks are the same, you should get nearly the same win rates, and in my simulation with 1001 matches per pairing you see only a 0.1% difference, which means the results are generally valid. However if you were to run a solution with only 100 matches per pairing, you might get a variation of 5-6% between these two win rates, which tells you there isn’t enough data to properly capture the decks’ strengths. If you have the time and can wait for the simulation to finish, more matches is always better.

I choose “Evl. AI (strong)” here instead of the stronger “Evl. Planner (med)” because it’s significantly faster, but once I narrowed down to a few candidate cards to remove I suggest running another test with the planner type to further validate things. Also because in “All play first” games the statistics tend to be a bit less stable,  you may want to run one or more simulations with “All play all” to see how your modified deck(s) do against a few different types of decks. For these follow up runs, you can simply delete the participants  you don’t care about and re-run a different simulation as needed.

Remember, each time you run one of these simulations you should expect to get slightly different results just because the random number generator will be a bit different. But if you have enough matches per pairing, you shouldn’t see the win rates change more than few percent points between runs. You’ll find a clump of cards which are consistently on the top (the weak ones) and another clump that are consistently near or at the bottom (the strong ones).

Deck Simulator for Hearthstone is currently available on the Apple App store for $0.00, and you can see the details of it here:


Deck Simulator for Hearthstone’s “HELO” rating system

Initially I thought it would be fun to write a simulator which implemented all the rules of Blizzard’s excellent Hearthstone game, and allowed me to experiment with different types of strategies. But the more I work on this project the more I try to think about how others might use this app to enhance their Hearthstone experience.

Playing virtual games of various decks is interesting, and can help you tune a deck to perform better in actual games. But I have a feeling that many people don’t want to execute several runs of simulations and then try and compare the results, since this can be a tedious process with various levels of interpretation. The deck simulator is an experimental workbench for Hearthstone cards, after all.

However, I thought it would be nice if there was an easy way to grasp a deck’s strength, something which would allow a ballpark understanding of it with a single glance.

What I came up with is “HELO”, which stands for “Hearthstone Elo”, where “Elo” is the rating system commonly used in many competitive games, such as chess.

The actual algorithm and it’s analysis can get a bit complicated, but in a nutshell it works by maintaining a rating of strength which decreases when you loose and increase when you win. The amount of ratings adjustment is proportional to the rating of the opponent, and the number of games played by both also factors in.

Deck Simulator for Hearthstone manages this rating for each deck in the system, which is updated after each game and stored for later. The rating is displayed in three places:

  • On the ‘Edit Decks’ screen (bottom right), where it is listed next to the total number of games played in parenthesis (Ex: 1568 (10000)).
  • On the ‘Simulation’ screen’s game results, on the far left in brackets (Ex: [1805])
  • On the Participants detail window which appears when you click on a specific participant on the Simulation screen.

For all decks which come with the app when you download it I’ve already ran some simulations and generated their HELO score, and also configured things so they don’t change much. If you create a new deck it will start with a default rating of ‘1500’, and for the first few hundred games it can change greatly depending on how it performs in the simulator. The most important thing is not the number itself, but how it compares to the existing decks in the database.

One of the challenges with this feature is that the performance of a deck depends on not only the deck composition but also the strategy used by the AI player. I could have added separate ratings for each AI player as well and combined ratings, but to keep things simple I just have generated the existing ratings using only ‘Evl Planner (med)’, which is usually the strongest AI. You can use any AI you like, but for direct comparison you should use the same AI player to the extent possible. If you want to reset a deck’s rating you can simply copy that deck (use the green “Copy Deck” button on the “Edit Decks” screen) and it will start over at a rating of 1500 and 0 games. Another thing to keep in mind is that the rating is not reset when you modify a deck, so if you planning to make serious modifications to a deck you might want to copy it first you can compare the before and after, and have a proper rating for both.

An interesting thing about HELO is that sometimes it doesn’t match up with the overall win percentages of a simulation run (even if all the decks started fresh). The reason for this is that a higher win percentage (say, when comparing two decks) means “this deck won more overall games than this deck”, but a higher HELO means “this deck beat other decks with relatively higher ratings than this other deck”. So you can imagine a generalist deck that is designed to win as often as possible (versus any opponent), versus a specific counter deck targeting the stronger decks, and these would have different HELO vs win rates.

Please try out the latest version (1.2) on the Apple app store (link here) and let me know what you think of the rating system.

If you happen to find a deck over 1900 or so (the highest in the database at present), drop me a line as I’m curious to see it’s composition.



Deck Simulator for Hearthstone – iTunes – Apple

Detailed per-participant statistics in the HS deck simulator

One of the new features in Deck Simulator for Hearthstone 1.2 is the ability to look at statistics for individual participants on the ‘Simulation’ screen. This can be done by clicking on the participant’s name in the bottom table either during or after the simulation finishes.

If you click on one of these you’ll see a window which gives this type of information:

  • Details for ‘Evl. Planner (med) > R’s Paladin Deck 1’ [deck rating 1805]
    • 62 % [avg turns 10] VS Evl. Planner (med) > Evolved Paladin 205
    • 30 % [avg turns 9] VS Evl. Planner (med) > Evolved Paladin 215

I’ve bolded the important information in the above excerpt and will describe these below:

  • Win rate against a specific other participant, which is listed as “VS XXX” on the same line.
  • Average number of turns the game lasted before the game ended

The first of these is useful if you are running a simulation in ‘all play all’ mode because the percentage you get on the simulations screen is the average number of wins vs. all other participants, so clicking on that participant will give you information about which decks/players it is strong against and which is is weak against. Another way to check this is just run a ‘all play first’ mode in which the first listed participant plays each other.

The average number of turns the game lasted is interesting since some decks are designed to win after a long, drawn-out game and others to crush quickly, so you can use this number to get some feel for that.

One thing to keep in mind is that if you view the detailed stats while a simulation is in progress it will continue running (and update behind the window), but the window’s stats will not update in real time.

In the future I may add some more information here about each participant. If you have any suggestions, please let me know.

In my next post I’ll talk about the ‘deck rating’ which was mentioned in the above example.


Deck Simulator for Hearthstone V1.2 Released on Apple App Store!

I’m very happy to announce Deck Simulator for Hearthstone‘s 3rd version (1.2) is now available on the Apple App store!

For this release I decided to take a break from adding new cards and focus on adding a few features that will make the tool easier to use and more productive.

For example, I’ve added a very cool feature that allows you to evaluate to what extent each card in a deck is contributing to it’s overall strength, and also added a rating system for decks to easily compare them (HELO = Hearthstone ELO).

For full details of the release please see the app’s page here:


The app is currently completely free, with no ads, though will only be this way for a limited time.

I’ll be writing some more posts in the feature highlighting some of these new features and discussing how to use them.

Deck Simulator for Hearthstone V1.1 released!

I’m very happy to announce V1.1 of Deck Simulator for Hearthstone has been approved by Apple and is currently available on iTunes as an iPad app.

The main purpose of this release was to address a few crashes that I discovered, and also reduce memory used by the simulator. This allows longer simulations to be run without them being stopped due to lack of memory.

One of the crashes occurred when attempting to play a simulation with a deck containing 29 or less cards. I fixed this so it doesn’t crash, but instead gives a warning so you know you are testing a non-legal deck. I decided to allow this because making decks with less than 30 cards can be fun, and even useful when doing deck construction. I’m sure some of you wondered what would happen if you could create a small deck with only a few cards, and now you can actually see how strong such decks would be.

Another bug I fixed was where the default simulation type was “All play all”, even though the button showed “All play first” selected.

I decided to add an extra bonus which is all the cards for the Warlock class (previously they were not in the database), as well as three sample Warlock decks to play around with.

I’m already working on the next release and hope to have that out in a few weeks, but in the meantime try out the latest version and enjoy!