Saturday, 20 February 2021

Nothing at the Bottom: MOSAIC Strict RPG Design

This blog post describes some experimental RPG design constraint, MOSAIC Strict. I'm defining it because I'm curious what kind of games result from applying them. (I have no idea!) I'm defining them 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.


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 itself, but it can't import them from another document and make use of them.

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.

  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 :)