This blog post is also published at nethack4.org.

Strategy headroom in roguelikes

Tags: roguelike strategy balance | Written by Alex Smith, 2014-07-07

This is a blog post I've been meaning to write for a while. I frequently see the same mistakes made in discussions about roguelike balance, where people are asking for things that are incompatible with each other. Here's my attempt to explain the issue of roguelike balance as I see it, via giving a method of describing how a roguelike is balanced: its strategy headroom. (This concept applies to other game genres too, but I'll focus on roguelikes here, because it's likely less interesting in other contexts.)

The basic idea is this. Suppose your character comes up against some situation in a game where they have multiple options for which strategy they're going to take. An obvious example is character creation: I can play a spellcasting character, or a melee character, or maybe a hybrid, in the vast majority of roguelikes, and most roguelikes allow this choice to be made at character creation. This is going, at least for a while, to affect what options are open to my character in combat. In NetHack, for instance, playing as a Samurai, I have an excellent weapon for the start of the game (a katana); playing as a Wizard, I have an inferior option (a quaterstaff), but I also have the ability to cast 'force bolt' on occasion and defeat dangerous enemies that way. One of these choices is going to give me a better chance at winning the game. The question is not "which choice is it", but "how much difference does it make to my victory chances which option I pick?".

There are two possible extremes for the scale here. One is "no matter who you are or which choice you make, it won't affect your odds of winning the game". There are two ways to look at this situation. One is that the game is "perfectly balanced" with respect to character creation. The other is that the choice is entirely meaningless; if nobody gains an advantage from either choice, then either success or failure has nothing to do with the skill of the player, or else the various options play so similarly that the choice is entirely cosmetic. This situation has a very high headroom; the player can mess around with their strategy at will without any risk of the game limiting their experimentation.

The other extreme is "one of these choices will guarantee you victory; the other will guarantee you are defeated". This is definitely a meaningful choice, now! However, it can be seen as unsatisfactory for other reasons: the choice is meaningful, but it's a false choice, in that only one option is reasonable to take. An unspoiled player may pick the wrong one, and lose, if the choice is not well-signposted. Or a player might want to pick one choice (because it fits in more with how they want to play the game, for instance), but be forced to take the other in order to have a chance of success. This situation has zero headroom; a player must follow the path that the game dictates for them in order to have any chance of survival.

There are plenty of other situations where players have to make this sort of choice. Suppose that I decided that I preferred to play a spellcaster this game, than a melee character, but a few rooms after starting, I found some otherwise highly desirable armour but that blocked spellcasting. A typical example in NetHack would be a dwarvish mithril-coat, which is in fact often found by early-game wizards, meaning that this situation is far from hypothetical. Many NetHack players would recommend me to wear the armour, at least if all I wanted to do was to win the game; an early-game wizard benefits more from the defensive boost than they hurt from the lack of access to their meagre spell selection (in NetHack, at least; other games may be different). Many players would refuse, however; after having made the decision to play a spellcaster, changing to a bad melee character would not really fit in with the way they wanted to play the game. Game designers have to make a choice here: do they want their players to have to wear the armour in order to get a good win rate, or should the game forgive this sort of technically suboptimal choice? This really plays into the distinction between low and high strategy headroom.

High headroom versus low headroom

So, knowing what strategy headroom is, we can look at some standard requests that players make in roguelikes. None of these requests are inherently implausible, and they all seem reasonable on the face of it. However, many of them are requests for higher headroom, and many are requests for lower headroom. It's not going to be possible to keep all these people happy at once:

Classifying roguelikes in terms of headroom

A long time ago, in the early history of roguelikes, there were two major roguelike "families", typically known as "hacks" (after Hack and/or NetHack) and "bands" (after Angband), and mostly dependent on whether the roguelike was initially inspired by Hack or Moria. Coming into the field of roguelikes more recently (probably around 2008), I found that this classification had mostly broken down, and strategy headroom gives us an insight as to why.

The thing is, that NetHack and Angband are both high-headroom games. In NetHack, the focus is on ensuring that players can play the game the way they want to, using features such as wishes, a variety of escape mechanisms, and enough interactions between items that there is normally some way to achieve whatever you want. I'm less familiar with Angband, but I know that it's possible to play the game in a very safe way (as seen, for instance, by the Angband Borg), and that most Angband players choose not to, which are likewise signs of a high headroom. (In general, the non-persistent levels of the original Angband, combined with its weak clock, mean that there's nothing really to prevent players from grinding any generatable item, if they really want to; choosing not to do so is a sensible choice, but it's just one valid option among many. This is not true of many later games based on the Angband engine.)

If someone's roguelike world were just NetHack and Angband, the distinctions between them would have to be made on fairly superficial grounds. The truth is, that these games are more similar to each other than many other roguelikes. Angband's levels can be infinitely regenerated. NetHack's can't, but randomly-generating items on the ground also drop as monster deathdrops, and after the first few dungeon levels, monsters generate fast enough and drop food fast enough that NetHack has no relevant clocks but the (very very slow) extinction clock, so you can farm almost indefinitely even without the use of any particular exploit. (Roguelike-playing bots are a good example of this. The Angband Borg had a policy of never moving on to a new depth until it already had all the items it needed to guarantee survival there; this is, obviously, very slow, but computers don't get bored. Meanwhile, saiph, a NetHack bot, got stuck in a delicatessen once, and rest of the level was entirely full of monsters by the time she eventually starved to death; if it hadn't been for the chokepoint that was the reason she'd got stuck in the first place, she could likely have survived on the level almost indefinitely.)

However, this is no longer a world of just NetHack and Angband, and so we have many other choices to look at. Where, on a scale from Angband to NetHack, do we place DCSS (commonly known as "Crawl", but the original Crawl was somewhat different strategically)? Or Brogue? Or some of the newer "roguelikelikes" such as FTL?

The answer is, that all those games lie way, way off the NetHack end of the entire scale; they're all much more different from NetHack or Angband than NetHack and Angband are from each other. DCSS has a classic low-headroom tendency of nerfing or removing effects that are generally useful to almost all characters; for instance, it intentionally has very few to no high-quality escape items. In Brogue, if you want to play a particular character, you're going to have to resort to start-scumming; the items you need to build, say, a casting character won't always generate. In FTL, which upgrades for your ship are sensible largely depends on what items you find; deciding that you're going to choose a particular pattern of upgrades from the outset of the game would make it much harder.

And, of course, the hack/band distinction was in trouble when it started, simply due to the existence of Rogue, which is by definition the original roguelike. Is it like NetHack, or like Angband? The answer is "no". Perhaps the clearest sign of this is that the game is often unwinnable because not enough resources are generated to survive to the end; this means that it is also sometimes winnable only with perfect play, because the player is so tight on resources that a single mistake would leave them unable to finish.

Instead, I propose "high-headroom" versus "low-headroom" as a more meaningful way to classify roguelikes. We can have NetHack and Angband at one end, and Brogue and Rogue at the other. (Incidentally, this is why I often recommend Brogue to players who ask me about which roguelike to play, even though I like NetHack to the extent that I'm trying to unofficially maintain it; if it's clear to me that a player wants a low-headroom game, NetHack is not going to be a good recommendation for them, so I may as well recommend a good low-headroom game for them.)

Consequences of a high-headroom game

Maintaining NetHack 4 has left me in a good position to understand the implications of a game with high headroom, because NetHack is one of those games. In fact, this is arguably the reason that I originally started AceHack, one of NetHack 4's predecessors, rather than contributing to another variant; I felt that the variants that made more radical changes to the gameplay were making mistakes in the way that they went about rebalancing the game, in a way that I couldn't quite put into words at the time. I can put it into words now, though: the reason I dislike many changes made in SporkHack and UnNetHack is that they reduce the headroom of the game without sufficient compensation. In SporkHack, if you want a good weapon, you sacfest at an altar; most of the methods of obtaining good weapons have been removed, but not that one. UnNetHack doesn't have anything quite as glaring, but its limitations on wishing mean that players are forced into more traditional (i.e. less resource-intensive) ascension kits, reducing variety in the game, because weirder strategies are too resource-intensive. (Incidentally, Slash'EM does not suffer from this sort of problem specifically; its problems are entirely different.)

Still, though, even though I dislike this sort of change, many other players like them; and if someone asks me for a NetHack variant with changes made to the game balance, fewer exploits, or the like, I won't hesitate to recommend DynaHack or UnNetHack. Having a higher or lower headroom is not necessarily a good or bad thing. A good practical example is that NetHack has lost many players to DCSS over the last 10 years or so, and the players that I talk to about the issue mostly give headroom-related reasons for the change.

There are several advantages that low-headroom games, which is what leads players to search such games out, and which can equivalently be seen as issues with high-headroom games. I'd like to look at these issues, and ways to mitigate them:

Consequences of a low-headroom game

There are many challenges with high-headroom games that lead players to seek out, or at least to think they want, lower-headroom alternatives. So what sort of things can go wrong as the headroom reduces?

Thinking about headroom

Finally, here's a list of questions for aspiring roguelike developers to help them focus on what their game is about. This post has hopefully highlighted why it's impossible to keep everyone happy, and why some apparently reasonable about when creating a new game, to help you focus on the philosophy. These questions don't have right answers, in general. But I feel that for any particular roguelike you design, you should know what the answer is.

  1. If players choose a character concept and stick with it all game, what happens? In particular, are they punished for their inflexibility?

  2. If a player makes a mistake (i.e. fails to conform to optimal strategy), what happens to the character as a result? What if the strategy's only slightly suboptimal?

  3. How many viable strategies are there for winning any given game? How much do they vary from each other?

  4. What is the reward, or punishment, for experimentation with what is possible in the game (either out of interest, or because the player is new/unspoiled and does not know better)?

  5. How consistent is the optimal strategy for your game? What conditions might cause it to vary?

  6. What (if anything) can the player do to influence which strategies will be viable in any given game? What about after the game starts (i.e. not during character creation)?