Saturday 20 February 2021

Nothing at the Bottom: MOSAIC Strict RPG Design

This blog post describes an experimental RPG design principle, Mosaic Strict. I'm defining this principle because I'm curious what kind of games result from applying it. (I have no idea!) I'm defining it very carefully because we live in a fallen world and shared understanding is fleeting.

MOSAIC is a set of criteria that might be true of an RPG text:

  • Modular
  • Optional
  • Short
  • Attested
  • Independent
  • Coreless

If all the criteria apply, then that text is Mosaic Strict. If only some (or none) of the criteria apply, then it's not Mosaic Strict. There are no partial points, it's all or nothing.

(If you use a hash tag for some reason, please use #MosaicStrict capitalization so screen readers handle it properly.)


Mosaic Strict RPG texts are meant to be used together with other RPG texts; each text only describes a portion of the rules that will probably be in use. One might describe an initiative system, another how combat works, another how gutter mage rituals work.

Anyone trying to have a pleasant evening of gaming will probably need to use several of them.

Modular: Any game text that explicitly claims to be
an entire, complete RPG is not Mosaic Strict.

This doesn't mean that all Mosaic Strict texts necessarily work well together! Any given pairing might be hot garbage. That's fine, because they're all..


Mosaic Strict RPG texts are all optional; you don't have to use them. Each play group will decide for itself which one(s) they are using. If a game text describes itself as mandatory, or necessary for the use of a certain gaming experience, it is not Mosaic Strict.

Optional: Any game text that describes itself
as necessary for play is not Mosaic Strict.

Please note that the modular and optional tests aren't about the rules of a text and whether they're "really" modular or optional; this rule is about how the text describes itself.


Mosaic Strict optional rules are concise enough to fit on a two-page spread, no more than 1500 words.

Short: Mosaic Strict game texts are no more than 1500 words.

This includes any and all words that are part of the publication, such as words in illustrations, the document's title, subtitle, headings, subheadings, byline, copyright notice, Mosaic Strict attestation (see below). If the text is longer than this, it's not Mosaic Strict.


If the game text doesn't explicitly say that it's Mosaic Strict, it isn't.

Attested: Mosaic Strict texts say they are Mosaic Strict.

This rule exists for three reasons:
  1. Mosaic Strict game designers, if there ever are any, have a slim chance of finding one another if their work is labelled
  2. It might help confused readers of your Mosaic Strict optional rules understand why it refuses to use the term saving throw for no good reason
  3. It makes the acronym work


Now the easy stuff is out of the way, here's a tough one, the rule that is really what Mosaic Strict is all about:

Independent: Mosaic Strict texts do not refer to the mechanics
or quantified state in any other game text.

By mechanics I mean any procedures (do this, then do this next, roll these dice, use dice at all) that tells you how to play. By quantified state, I mean any use of numbers, tags, attributes, binary or multi-state conditions (alignment, prone, not prone) to characterize what's going on in the game world.

Mosaic Strict texts don't refer to any rules whatsoever from other documents. Mosaic Strict texts do not build on one another, they don't assume you're using alignment or levels or that you have a Strength stat described in another document, none of that. There are no mechanical connections whatsoever between Mosaic Strict documents.

This means that a Mosaic Strict game text that describes a turn order for combat cannot assume that characters have Dex scores, or that the game is using 2d6. The combat turn order document could define those things

Now, game worlds have things that can be counted or quantified: money, a PC's height in inches; light switches flip on and off. A game text can refer to quantified things that exist in a setting and still be Mosaic Strict.

A two-page spread about being a wizard could say that you need $13,333 to join the magic society and that you must devour 13 white cats to be able to cast a tree-climbing cantrip up to three times a day and could still count as Mosaic Strict; these are all in-game quantities.

A game text that references any mechanical quantity from another text is not Mosaic Strict.


This isn't a separate rule, but a consequence of Independence that I need to be really clear about: There are no core rules and no character sheet at the bottom of Mosaic Strict, no standard interface of compatibility.

Coreless: assume nothing else is in use beyond free-form play

A game text could define a character sheet and still be Mosaic Strict, but any other document that requires its use is not Mosaic Strict.

A game text could define a universal resolution mechanic and still be Mosaic Strict, but any other document that references that resolution mechanic is not Mosaic Strict.

There's no central document or required rule at the heart of it all, only free-form play role-play and whatever assumptions a particular group brings with it.

A Few Clarifications

Q. Is this gatekeeping bullshit?
A. No! Or at least, I hope not. I intend this in the spirit of the 200-word RPG contest: a very specific set of rules to see what comes out of it. My first few conversations about this convinced me there's a powerful temptation to do almost what I'm describing, slithering back into much more normal game design, so I want to be really, really clear about what I'm talking about.

Q. This sounds stupid, how does this make a better game?
A. I doubt it will!

Q. Is there any Mosaic Strict actual play so I can see what the fuck you're talking about?
A. No. The Mosaic Strict criteria are meant to apply only to RPG game texts. They don't apply to play styles or culture, design aesthetics, genres, or anything else—just the text of the RPG.

This means that if a bunch of people get together, grab three Mosaic Strict documents (one for being a wizard, one for stealing things, another for driving too fast in a jalopy) but bring along their 5th edition play assumptions and experiences and use a d20 for everything, the criteria of Mosaic Strict have nothing to say about their play experience. If a group is playing Call of Cthulhu mashed up with cool take on slime infection in a Mosaic Strict two-pager, we don't say that their session was Mosaic Strict or not.

All play experiences incorporate elements from the players that are not in the rules. Mosaic Strict only applies game texts, not play experiences.


  1. You're a mad man! Seriously though, this is a really interesting idea. It would not be as strong if you didn't define it so exactly so i appreciate what you are trying to do. This set of constraints could produce some really interesting design!

    This is the kind of thing that feels really perfect for an game jam if it can grab some steam. Then players could have a menu of different modules to grab for a Mosaic Strict game.

    1. That would be fabulous! I think if this ever goes anywhere it will have a slow start. :)

  2. A bunch of Levi Kornelsen's stuff, especially Situations for Tabletop Roleplaying, would fit (minus the Attested, of course, because he's not a time traveler). Even more are semi-Independent, in that they might tell you to apply a typical bonus to the core RPG's action adjudication mechanism, but it's up to you to adapt what that means in your system (might be Advantage in 5e or a +1 in PbtA or a +2 in Fate, etc.)

    1. Very cool, Robert; thanks for the reference.

  3. Regarding the "S", how would you rate text that is partially obscured, for instance a javascript generator on a blogpost?

    Whatever the case, this is fascinating, M O and C are the most interesting elements to me. It also isn't hard to see how things can be made broadly compatible - "Strength 15" becomes "as strong as a bear"

    1. For code, you need to count each token, so:
      { "class" : "Ranger", }
      count as as ten words! In all seriousness, I don't think this test can apply properly to software or dynamic documents.

      But yes, using qualitative measurements of things seems like a solid way to go to bridge the gap between different MOSAIC Strict rulesets.

  4. This is an interesting concept to think about, almost like the unix software philosophy, where all programs should be simple and focus on doing only one thing. From a game design standpoint it seems a fine way to focus down on the core of the idea without worrying about implementing it in a specific broader system.

    It does seem like however that it's gonna add some amount of "player overhead", for lack of a better term. If every subsystem implements their mechanics of different resolution methods, the resulting system will be more harder to learn than a similar holistic system. I suppose that's helped by the simple requirement.

    Similarly while using something like spwacks mention of "as strong as a bear" to keep the concept of strength broadly compatible works fine for simple uses, I think it's gonna be harder if you want to make something like a drain strength spell. Of course one could go the route of just making it something like "you become as strong as a mouse." But it seems harder to me if the spell should affect strong and weak people equally hard (Something comparable to a strength -3 spell).

    But since you're pitching this as a design constraint that may just be an area that get's constrained away.

    1. Yes, I think you're right. Not all designs are easy or practical to implement this way. The 3.5e-like approach where there's a standard resolution mechanic and everything latches on to it by adding modifiers, re-rolls, etc. becomes impossible. My guess is that strength drain type spells would tend to turn into instantaneous effects. "You drop d10 objects you're carrying," for instance.

    2. I think one way to solve player overhead is to take some prep time before play to "synchronize" the rules. If there are any overlapping concepts in each module then come to a decision about how to combine them and get going. There would still probably be some overhead thought.

      As far as strength draining there are other options. "Your strength is halved" does not mention other rules text. Another option "your weakened as you would be by a high fever" which actually has a distinct effect from something like "-3 strength". I don't losing the granularity of a spell draining -3 strength because fictionally, if your body is being drained what will probably make less coordinated and slower to think as much as it causes you to be less able to carry things. How the effect gets translated depends on if your modeling vampires sucking blood or everything withering and rotting under the sight of the evil idol.

    3. Player overhead wouldn't come into play if they are mostly or totally thinking within game world fiction, letting the referee decide what rules, if any, apply.

      Michael's idea here doesn't assume a game style where players are doing heavy lifting with rules. All the better, because the modularity and independence would make it easier for the ref to swap out 'subsystems' as the context demands it! And the players would not have to know or care.

      Page 22!

  5. I really like this idea. It reminds me of the "mini games" you'd see in some old modules ("Something Rotten in Kislev" is a good example, as it has a few) that exist only for a specific setpiece in the scenario. I always enjoyed those, and pushing this idea further (even further than things like AD&D thief skills or WFRP2e Magic system) would make for some cool, idiosyncratic experiences.

    Also, it would be a fun design challenge.

    If you ever host a jam - I'll be there :)

  6. This is pretty neat! I found your post through The Glatisant, and I happened to read it as I was thinking about how I run games when I don't have dice or paper. I wrote up my resolution mechanic using MOSAIC Strict as a scaffold.

  7. Hm. I like the idea. Feels like a convergent evolution to the GLOG.

  8. This is great - I just really love the idea of this taking off and then we have all these little modular stuff that fit together strictly through attention to the fiction.

    Some offerings:

    dream interpretation

    I think I'll keep on making more of these, but the best part is that if what I make sucks, it doesn't ruin anything else. (You can even have two "general" combat systems in your pocket and choose based on whether you want combat as war or combat as sport based on a read of what your players are feeling, say.)

    1. Hey, great stuff, Matthias—I'll put up a blog post soon summarizing all the rule sets I'm aware of, and I'll include these.

  9. Is it Mosaic Strict to elaborate on or give suggestions for how the module might interface with other modules?

    e.g paragraph 3 in this toy example:
    "Attribute Generation: You have 3 attributes: Strength, Dexterity, and Will. Assign the scores [2,1,0] to them in any order.

    "To make an Attribute Test, roll 1d6 and add the relevant Attribute Roll is 1d6 + Attribute. 5+ is a success.

    "In addition, Str, Dex or Wil scores may add that many extra dice to a dice pool, extra pulls from a card pack, or extra narrative currency to spend on a nonrandom game procedure."

    1. No, that's expressly prohibited. The rule against this is arguably the most important thing in all of Mosaic strict. :) From the spec:

      Independent: Mosaic Strict texts do not refer to the mechanics or quantified state in any other game text.

      Mosaic Strict texts don't refer to any rules whatsoever from other documents. Mosaic Strict texts do not build on one another, they don't assume you're using alignment or levels or that you have a Strength stat described in another document, none of that. There are no mechanical connections whatsoever between Mosaic Strict documents.

    2. It makes sense to draw a bright line like that, I just wasn't sure how literally (or, uh, strictly) to read the Independent rule.

      But I can see now how you mean "Mosaic Strict texts do not build on one another" to mean no references or suggestions, not just no dependencies.

  10. Would it be Mosaic Strict to make several modules that do not directly reference each other but are designed around the same resolution system, but each module describes the resolution system independently?

    On a similar but not exactly identical question, would it be Mosaic Strict to make design a set of modules that are meant to work well together, if they also perfectly well independently and don't make references to the other modules?

    I'm thinking of the idea of taking a game and breaking it apart into a set of Mosaic Strict modules, and I think you could be able to do it but it would result in unnecessary redundancy, and the requirement of everything being Optional could change how and when rules are applied.

    1. To be somewhat pedantic, it's only the individual modules that are or are not Mosaic Strict. The criteria don't apply to games, collections of modules, game play, etc.

      So yes, you can write multiple Mosaic Strict modules that redundantly explain the same resolution system, that doesn't make them not strict.

      As for "meant to work well together," that's totally fine as long as that means that they're complimentary, orthogonal, and perhaps jointly cover enough areas for a complete game experience. If they build on one another by direct reference, then no, whichever modules do that aren't Mosaic Strict.

      Writing a module that only makes sense in context of another, specific module breaks the spirit of Mosaic, but not the letter of the spec.

      One extreme end of this would be two mosaic sets - one describes a set of holy prayers and their mechanical effects. Another has the same list of holy prayers (these are in-world things, like monster species, not mechanics) and describes something else mechanical about each one, such as the required components. Apart from being inconvenient for gamers, this is really not what I was going for with Mosaic Strict, but it's totally legal per the spec.

    2. I'm asking for a somewhat niche elaboration so a somewhat niche clarification makes sense.

      That's what I assumed the implications of the specs were, thank you I think I understand it.

  11. Hm, this is extremely fuckin neat, and touches on some thoughts I've had about a tome of independent rules modules, might try to attempt that while making use of these specs.

  12. Seems like you would run afoul of Gödel's theorem of incompleteness at some point. Maybe you can take your work in for some Maths credit. :)

  13. Howdy. Paul Czege turned me on to this, and I gave it a whirl:

    1. Skirting close to the edge by calling it a game, I see! How do you want to be credited, as 'Luck of Legends'?

  14. Eek! Not sure why it posted me as Unknown - I'm Michael Low (please use my name, thanks!), and it's a pleasure.

    I started with a simple chargen system, then thought to offer some quick-play stuff I'd used ... it spiraled. If it doesn't qualify, let me know and I'll remove attribution!

    FWIW, I find the ethos completely compelling. I've tried making a game which had "Story LEGOs" as a design goal, and this seems more modular, creative, and functional - it acknowledges no gap between the rules and the experience they create, while celebrating mashups.

    It's very inspiring. I dig.

  15. Made a MOSAIC Strict doc for playing duels between mechs: Cheers!

  16. One of my buddies (Wafergix,) made a lot of MOSAIC Strict works - in Polish and English :

  17. This is great! I have launched a jam for this at:

  18. Just found this — very cool, Michael. Although it hurts my heart to see "Independent" used in this way when since the late 90s it's meant independent in the way comics and music use the term — creator-owned content. Sorry, not content. That's a bullshit term. Art. Creator-owned art.

    Anyway, "Coreless" seems to fit the bill by itself, so I'd throw the suggestion to you to make Independent mean creator-owned. YMMV. Your stuff continues to be great.

    1. Creator-owned comics and music are great, but words have lots of meanings, it's all contextual. As a coder with a statistician parent and a therapist spouse, 'creator owned' doesn't even crack my top 5 strongest associations for the 'independent'!