Converting Codex to 5E (and 5E into Codex)

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    Hans Hellinger

    From J. Scott:

    [in 5e]
    “(round as 6 seconds just as in 3.5, but it has a Movement, a main Action (which could include multiple attacks or just one, depending on the class and level) And both a bonus action (when applicable) and a reaction (depending on what happens to you not on your turn in the initiative). Which gives you versatility for what to use for your action and reaction, or however you use it.”

    I think Codex is actually much simpler than that. You just have your 3 or 4 MP, which can be attack, defense, movement, counterattack, or anything else you want to do. You don’t have to think about whether what you do is a move action or a first or reaction action, or an attack of opportunity, they are all the same. 1 MP lets you do one thing, or you can spend 2 or more and improve your odds. And then some feats give you an extra MP circumstantially.


    My group should be doing a 5e game starting up somewhat soon and we’ve made characters for it, so I’ve been digging into it a bit more and hope to have a better feel for it in play in a few months. From what I have seen so far of 5e the above should work well enough for just replacing the usual actions (Action, Movement, Bonus Actions) with Martial Pool (although the base rules effectively give you a bit more flexibility up front simply because you have more available to you than a single MP die will give you at 1st level in Codex Martialis, FWIW). That being said, I’ll have to dig into it a little but but MP would need to be based on something other than Base Attack Bonus, since that doesn’t really exist in 5e.

    Most everything is rolled as a straight d20+Ability Modifier (a bonus or penalty based on the Ability in question, such as Strength or Dex). If you are also Proficient in a skill being used for the roll you also get to add your Proficiency Bonus, which starts at 2 and increases by 1 every 4 levels, no matter class or anything else (even multi-classing, which in many ways is also simpler and easier to do in 5e).

    So arguably MP could be based on Proficiency Bonus (either equal to it or more likely by subtracting 1 from up up to your MP limit of 4.) This would mean that MP is strictly a level-based mechanic and would seem to be the closest analogy to BaB in 5e, it’s just that class doesn’t affect it like it would in 3.5. That’s probably not a problem because, as we both know, people are in many way a lot more flexible and capable than previous editions of D&D tend to imply with a strict class system. This does make it a little easier to deal with leveling up a bit higher than, say, 6th level as you’ve suggested elsewhere as a method for tamping down the usual power curve (or overpower curve, as the case may be). In essence at equal MP would hit 4 at 9th level (and sticking at that ceiling at 13th level when Prof. Bonus would go to 5) or maxing at 13th (and not going higher at 17th) if making it at -1.

    I think my personal take would be to make it equal to Prof. Bonus. That is 1 more die than normally available under the 3.5 version at the lowest levels, but it help to equalize it a little to the 5e rules in that it gives you a bit more flexibility in actions anyway than earlier rules did, but it will slow down MP gain a little (especially compared to, say, a 3.5e Fighter).

    Feats are largely still there in 5e, although the “Feat” system changed a bit. There are class “Features” and you only get “Feats” (if using that “optional” system) when the class would get a Feature called “Ability Score Improvement”, which is around every 4 levels (4, 8, 12, etc.). You may choose a Feat instead of improving an Attribute by 1 point. The rest of the “Features” are otherwise kind of set in stone, although some Classes have a little flexibility with an “Archetype” you choose at 3rd level which gives you a branch of Features you’d be getting in the future. So some Features all members of a given class will get at certain levels, whereas an Archetype patch will give different Features based on the Archetype at some levels.

    My take here is really the same as the BaB note for above, since CM simply adds “Martial Feats” as an addition to the standard Feats system in 3.5 linking them to BaB, although in this case they could be linked either to Proficiency Bonus (take one Martial Feat for Prof. Bonus, for example, which starts you with 2 instead of one, or Prof. Bonus-1 starting you with just 1 and getting a new one every 4 levels) or linking to the Feats system (you may also take a Martial Feat in addition to the usual “Ability Score Improvement” or Feat). The latter method would mean you start with none (unless you added a rule to allow for 1 or 2 MFs to start with) but would also mean you get a MF 1 level sooner than the former method (at 4, 8, 12, etc. for Ability Score Improvement rather than 5, 9, 13, etc. for Prof. Bonus).

    In essence probably the biggest change here is that Class in 5e is disconnected from what had been BaB, and BaB is used as a core point of reference in CM. The biggest “Class” this effects, then, is Fighter since they would gain a BaB at every level, so they would be getting a lot more MFs (and gain MP very, very quickly) compared to what they will get using CM in 5e when linking it to Proficiency Bonus or to when you get Feats. So I think that may have to be considered for what seems to play well when using CM with 5e. (Not to mention dealing with the Class “Features” to see what is appropriate for use with CM or if any should be modified in some way). Advanced MFs would need a modified BaB requirement as well, of course.

    I will say that so far I’m liking what I see in 5e. In some ways it uses a bit of a mechanic not dissimilar to CM in the sense of loading the details onto the sheet before play so it’s just a quick check of what to add or subtract from a roll and comparing it to a target number. Any table lookups and such are done beforehand to just get that bonus to use. Situational modifiers to a die roll generally come down to a single mechanic of having “Advantage” or “Disadvantage” (and if you have both they cancel each other out so you just make a straight roll). Having either just means rolling 2d20 instead of 1d20 and taking either the higher (with Advantage) or lower (with Disadvantage) roll. In essence what you kind of do with saying you want to give yourself and advantage by rolling 2 dice from your MP for, say, attack or defense in CM, but this same mechanic could be used for situational modifiers to CM as well, such that you take an extra die when rolling with Advantage (already a CM mechanic, after all), it’s just if you want to use Disadvantage to, say, remove a die (or add a die if down to 1 and take the lower result) as a way to use the same mechanic in CM.

    Outside of that some pre-requisites may need to change just because some reference regular Feats that aren’t as freely available (or might not even exist now) as they might have in 3.5e.

    Those seem to be the main concerns of trying to use CM w/ 5e, I think, from going through things so far. Superno may need some tweaking as well, but I THINK maybe a lot of that will be less affected by 5e changes than CM itself would be.

    Hans Hellinger


    Thanks a lot for your interesting and detailed analysis here. I have also been talking to two of our playtesters about this specific issue quite a bit as well.

    The good news as far as integration is that as I mentioned in the first post (which was copied from an email discussion with one of those playtesters) the MP system should rather seamlessly replace all the different kinds of actions (attack, counterattack etc.) in 5E, and is actually simpler. It also rather seamlessly replaces Advantage to some extent, as most Feats and some other basic mechanics like aiming with support or using cover just add MP – though applying it in some other circumstances might still need to be looked at. To be honest I think they stole the ‘Advantage’ mechanic from me.

    The general issue is one of simplification. The plan is to remove the 3.5 Feats, BAB, and some other 3.5 ‘baggage’ and thus make the whole thing a bit more manageable and familiar for 5E players. This is going to be first tested with our new Star Szkola variant (next on my list after I finish Codex Baltic Volume II).

    However there is a slight conundrum, a cultural difference if you will, which is that Codex is I think going to need to keep more options including in the form of Feats and Skills, than 5E players are used to. I’ll need to figure out how to handle that. This is in part due to the way the character generation works.

    Doling out MP and To Hit bonuses and so on is also tied closely into Character Generation. I have posted a limited preview of the character generation system “Codex Ingenium” in this thread here

    Codex Ingenium Discussion

    This doesn’t quite get at the meat of the issue though because I couldn’t post the tables and it doesn’t include the specializations (similar to the subclasses in 5E, but historically based). However, the basic goal of simplicity is still there. There is no need for PC’s at least to understand all the skills. The approach is just different. Instead of hand waiving the idea of training or skill acquisition by focusing on ability score checks, Codex is meant to allow a lot of specialization based on your life experiences, but the central conceit that keeps it simple is just that, you don’t have to worry about the specifics so much. If you have a skill which sounds like it might be applicable (or you can spin it that way to the DM) then you can use the bonus on your die roll.

    In other words, you might have a scholar with a Knowledge: Geometry +4 or an Artisan with a Knowledge: Engineering +4 or a soldier with a Knowledge: Fortifications +4, but any of these skills could be used to enhance a skill check for trying to figure out how to sneak into a castle.


    The Skill thing isn’t necessarily an issue. Even the SRD under has a section for “Variant Skill List”. Alternately you might consider just stating that the lifepath generated at a certain point gives you “skill in blah-blah, which give you Proficiency in Athletics”, or whatever is appropriate. Per standard rules if you get Proficiency (or a Tool, don’t forget you have those as well) a second time it just means you get to choose a Proficiency (or Tool, if it’s a Tool) in its place. I’ve mentioned before (I think in that thread) that my concern with lifepath generators is if they constrain a player too much then they can be problematic so having situations arise where a character might already have a Tool Proficiency of, say, Smith’s Tools because of an apprenticeship, or something, but then ended up with, I don’t know, a merchant thing that would give them the same tools for some reason, then letting them say “You know what, since I already knew smithing and had those tools, during that time I actually took the opportunity to learn some of the Masons art!” and get that as a Tool Proficiency seems just as good, IMHO.

    And definitely don’t forget that while Skill Proficiencies are broad and seemingly limited, all of those Tool Proficiencies are where a lot of the old “Skills” actually went to! So you definitely still have all of that flexibility there.

    I think the difference is you’re effectively creating a more granular version of the standard “Backgrounds” system is all, IMHO. Nothing wrong with that at all, I don’t think, especially if you use that to kind of make up for the whole BaB disconnect, if you will.

    I largely do agree that the Martial Feats need to stay, however. I’d probably suggest that, like they are for the 3.5e version, they should be an add-on to the Feats system and not integrated directly into it anyway. And that should cover it. After all the main thing to consider is always balance and as long as both the players and the NPCs they face are using the same system then you naturally have that largely built in, so I don’t think it would be a problem.

    Hans Hellinger

    Thanks, I didn’t (and still don’t fully) understand what a Tool or Tool proficiency was. I’m still learning 5E

    The lifepath character generation system I have now is a bit different from the old one in several ways. One is that as you make your character you get kind of abstract points that you distribute to specific things when you are done. This was in part to make the whole process move a lot faster, but it also means that whatever you end up with will make more sense. In other words, you wouldn’t pick up skills, feats or kit at age 17 during your apprenticeship as a smith, you’d gain the potential of something which you would “spend” later when your character is finished (maybe at age 25). So you can pick whatever makes sense to you at that point, based on whatever other jobs you had.

    And yes, I think the Specializations in Codex Ingenium line up fairly well with the “Backgrounds” in 5E.

    Right now I’m in the process of removing as much of the 3.X stuff as I can, the only limitation to that is to make sure all the books line up so that things don’t get out of synch.


    So, to be perfectly honest, it doesn’t seem to me that there is any real difference between a Skill Proficiency and a Tool Proficiency, they just seem to be categories of Proficiencies and Proficiencies seem to just be equivalent to 3.5e Skills. Arguably the main difference being that in order to use a Tool Proficiency you need to also have a piece of gear, the Tool, used for that proficiency, is all.

    Hans Hellinger

    Gotcha, makes sense. I’ll look at it! Thanks for helping me decipher another part of this …

    Hans Hellinger

    Does anyone know if 5E uses the term ‘DC’ as a target number for skill check rolls? I’m wondering if that’s another thing I need to remove like ‘BAB’


    Yes. From the book to reference the general DC comparisons:

    Typical Difficulaty Classes

    Task Difficulty | DC
    Very easy | 5
    Easy | 10
    Medium | 15
    Hard | 20
    Very hard | 25
    Nearly impossible | 30

    Probably the better (base) SRD site to reference the above would be at

    • This reply was modified 3 years, 3 months ago by zarlor.
    Hans Hellinger

    Awesome thanks


    FWIW I’ve been doing a really deep dive on 5e lately and I really think it may be the way to go here. I mean OSR isn’t some kind of pre-defined rules you can plug into or anything, but 5e is. While I have many pages of notes I think most of it really boils down to minor tweaks.

    Classes in 5e do a lot of the heavy lifting for “Features” so something between Classes and Backgrounds would probably be where you would truly create a Codex Integrum “flavor”. That heavy lifting, though, may also be where you need to do a bit of tweaking for folks using the core Classes. In essence, though, I think the big thing would be to say something like “Use the Martial Pool mechanic in any situation in which you are using combat rounds”. Then modify the SRD definitions of Advantage to just be adding a Free Dice and Disadvantage as removing a die from the MP (or current MP roll? I wasn’t sure on that) unless doing so would bring the MP to 0, in which case roll 2 dice and take the lower result. Unlike the SRD you might add that you can have more than 1 case of Advantage or Disadvantage for a roll. Then for consistency sake you can replace using the phrases “add a Free Dice” or removing them with just saying you have Advantage or Disadvantage for the roll. Easy. MAYBE a review of how a 5e “Bonus Action” fits in may be helpful, but largely I think the above covers any situation where you have one that would affect the MP.

    The term BaB in CM can probably be straight up replaced with Proficiency Bonus. (Proficiency Bonus is just level-based, so every Class just gets it the same way). But 2 things are based on that, MP size and when you get Martial Feats. So is a standard MP of 2 at 1st level, 3 at 5th and 4 at 9th good enough for that? Ditto for Martial Feats? Personally I think the former might be fine (depending on if you level cap or not, although 5e is a bit different here, too, but I’ll need to do some playing to definitively say if level capping is still needed to keep some of that feel to it or not), but I think the latter may be more problematic and may need to be linked in some other way. (If you linked it to Feats, of which the SRD only has 1 anyway, you would get those first at 4th, then 8th, 12th, etc.) I kind of think that will need to be addressed. Maybe one every other level? So 1, 3, 5, etc.?

    You will need some slight revisions for any “negative hit points” statements you have, since you bottom out at 0 now (the only thing below 0 is if that last blow would be negative enough to equal your hit point total, in which case its insta-death. Otherwise you’re at 0 and either making saves to avoid death, or someone has to, well I guess we used to call it “bind your wounds”, basically.

    Criticals should probably be reviewed compared to 5e, but changing the CM version may or may not be needed. I have some notes about it, but they may be worth reviewing, is all. Same with some of the equipment lists (mainly to either get rid of some fields no longer used in 5e or to just make sure you define them in Codex if they are still needed there anyway) and maybe a little review on Mounted Combat, but overall Codex Martialis should be a relatively easy plug-in to just use the SRD for 5e and you’ll be good to go (and have a game system a WHOLE lot easier to deal with.)

    Less important, though still referenced in a few Martialis spots, would be “Skills”, in essence these are just Proficiencies in 5e and there are 3 types, Skill Proficiencies, Tool Proficiencies, and Languages. Most of them are granted by either Class or Background and having them just means you get to make the roll with your Proficiency Bonus (so just a level-based modifier, if you will). Tool Proficiencies just mean you have to have the “tool” kit for that Profciency to even be able to roll. Otherwise it’s just noteworthy that the Proficiencies are simply broader in scope now so you’re not drowned in a bazillion little “skills” to choose from. Considering that a common problem I’ve long had with skill-games like 3.5e is that historically people are a lot broader in skill than you could usually be by those rules I’d say this is another big advantage to broad proficiencies over focused skill lists.

    Integrum would need a bit more of a deeper dive to get it jibed up, but that’s mostly just because of things like Spells being case from a level slot rather than always based on the caster’s level, so even that isn’t a huge deal. In other words Magic Missile is no longer automatically adding bolts because you’re a higher level caster, instead you have to use one of your higher level spell slots to do it, an that greatly reduces the damage some of those things did, too, since it’s not about caster level anymore but about spell level instead. That and cantrips are just always available to cast as an Action. There are a lot more little things including reviewing the new spell lists (remember you only need to address what is in the SRD, though, as nothing in the PHB would be something you’d bother with).

    Still, while I have many pages of notes it took me only maybe 6 hours of solid work, if that, to essentially prove to myself that 5e is likely going to be the easiest way to go to fill in a game system for what CM doesn’t cover with really just some relatively minor tweaks to CM and, IMHO, fill in plenty enough of what OSR does anyway (besides just making sure to explicitly state that Rule #1 in CM is to “just wing it when you need it” practically covers the biggest thing OSR is supposedly trying to pull back into gaming). I’d be happy to sit down (or conference/phone call it if you’re still more COVID-averse right now, since I haven’t gotten the shot just yet) and go over these some day if you really want to see what I’ve got figured out with it.

    Hans Hellinger


    Thanks again for digging into this. I’ve been looking at 5E as well. The short version of my reply to the above is, now that Medieval Baltic Vol II is finished, I am pivoting back to the Codex rulebooks and have already started work on ‘modernizing’ them. Certain decisions have been made, but the TL:DR is as follows:

    1) We are making a streamlined 2021 edition of Core Rules (et al) with most of the 3.5 specific Feats, rules and terminology (like BaB) removed, and some additional role playing rules (as distinct from just combat rules as current) added. This will also have some terminology which is ‘5E friendly’ like using the term proficiency. The 2021 version will be basically ‘system agnostic’ and ‘system lite’ so as to be easier to adapt to 5E or OSR RPG variants.

    2) The adventure module, Road to Monsterberg, has already been adjusted somewhat along these lines based on playtest feedback, and will be brought further into sync with this general system reform.

    3) Once this is complete we will begin to look at layering in some of the rest of the 5E terminology and rules (by either including them or more often, explaining where they are replaced by Codex rules) so as to be in full compliance with the 5E OGL contract. The goal is to include this in a somewhat modular manner rather than the way 3.5 was tightly integrated into Codex previously. That way whenever the newer version comes out we won’t have this same problem.

    4) Then we are going to finish and release the Character Generation book, Codex Ingenium, which will be designed to be 5E compliant (though obviously, it’s different in many ways). Some of the philosophy of the approach we are taking to this has been discussed in some detail here.)

    I’ll be glad to bounce this off of you and consult with you on the revisions as they come out, I can definitely use all the help I can get.

    As for OSR vs. 5E, that is more of a gamer culture thing. The mainline 5E audience seems to be wedded to some ideas like automatic overnight healing, player character death being frowned upon, automatic spell casting and spell recharge, and so forth, and an overall emphasis on high-magic, high-level play which isn’t really compatible with Codex or the idea of historical gaming. That said, if people want to try to adopt it for that I am 100% ok with it! But I’ve found that whereas 10 years ago Codex was made for people who liked to tinker with rules and fold them in to their own house systems, now days it seems like a lot more of a soup to nuts level of completeness is required for a lot of gamers. So as far as a complete seamless system, we will be adapting to 5E rules, but leaning more toward an OSR game style. Some people do run OSR campaigns in 5E.

    Culturally, OSR seems to be a better fit with Codex – at least that is our current conclusion. This is because it’s more typical to have low-magic, low-fantasy settings, without very high level game play or comic -book style super powers and so on, and the idea of player mortality is not a third rail.

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