Modding Arcanum: Character Backgrounds

Start here to get familiar with Arcanum's text files and create your very own character background!

Overview

This guide will open the door to modding Arcanum. Nothing fancy here, and no extra tools required besides DATBuilder[drive.google.com], which we'll get to shortly.

MES files are Arcanum's text files. They can be opened up in Notepad or any text editor. They contain ALL the game's text-based data, such as names, descriptions, buffs/effects, and the ID numbers the game engine uses to manage and link them. In this guide, I'll make sure you're familiar with MES files by walking you through the creation of a custom character background.

DAT Files

DAT files are the compressed archives containing all the game data for Arcanum. Extracted files will take load priority over the DAT archives, so if anything goes very wrong, you can simply delete the file and the game will use the one still archived. That being said, I still recommend keeping backups of your files, just in case.

If you (or something you installed) have already extracted the proper files, you shouldn't need to extract anything. To verify, open steamapps/common/Arcanum/Arcanum/data
And see if the following four files are present:

In the "mes" folder:
• description.mes
  
• gameback.mes

In the "rules" folder:
• backgrnd.mes
  
• effect.mes

If any of these files are not present, you will need to extract them. If they are all present, you may skip the rest of this section (though I recommend making backup copies of them somewhere).
For the purposes of this guide, you only need the "mes" and "rules" folders which if you're using vanilla Arcanum are contained in archives 3 and 4. If you're using the UAP[terra-arcanum.com] without any options, it'll be Arcanum5.dat, and if you installed the Race Mod option with UAP, you'll need to extract from ArcanumXRaces.dat instead. Failing to extract from the proper DAT file may cause other parts of UAP (or other mods/tools you're using) to function improperly. If you're not sure, just ask in the comments.

Note: If you plan to do any more serious modding and wish to extract all the files, extract them in order from Arcanum1 through to the ArcanumX files; the order is very important since that's how they're loaded by the game.

Start by downloading and running DATBuilder[drive.google.com]. It does not need to be installed in the Arcanum directory to work.
(Note: A Google update may have broken the link for many people, so let me know in the comments if it doesn't work for you so I can continue to troubleshoot it. There are other places that host it though, so you should be able to find it via a simple search.)
Then, simply 'Open' the proper DAT file from Arcanum/Arcanum, then 'Extract' it to a separate folder of your choosing - I recommend creating a separate "data" folder somewhere easy to get to and extracting the DAT files there to keep the same file structure.
Again, note that only the stated DAT files are required for the purposes of this guide, and should load and extract almost instantaneously. Arcanum1 and 2 are generally larger as they include art, sound, and other such files, and may take a few moments to even load.

Finally, verify that they have been properly extracted by looking at the your extraction folder and finding the four files mentioned above:

• data/mes/description.mes
  
• data/mes/gameback.mes
  
• data/rules/backgrnd.mes
  
• data/rules/effect.mes

Copy these files over to their proper place in the Arcanum directory in Arcanum/data, and then open them using Notepad or whichever text editor you'd prefer. Don't overwrite any files that are already present- they may have been added by another mod or tool you're using.
Once that's done, we may continue.

Description.MES

Regardless of what you plan to do with Arcanum, you'll need to become very familiar with description.mes. It is the file that contains all the names for every item, entity, and tile. We won't be modifying this file in this guide, but we will need it as a reference for later, so keep it open.

For now, just keep in mind that different types of items are separated by the thousands: weapon names start at 6000, armor at 8000, etc. Feel free to scroll around and see what the other sections contain before moving on.


Also, we can see here the standard layout for MES entries:

{ID#}{data} //comment

In all the MES files we'll be working with here, they follow this format. Keep it in mind as we continue.

Gameback.MES

The next file we'll be opening up will be gameback.mes, which contains the actual name and description for character backgrounds. This will appear when you create your character, and in-game in your journal. Keep in mind there is a size limit for the text, so writing one that is too long will be cut off in the creation screen (and, to a longer extent, the journal).
You'll want to scroll all the way down to the last entry, which in Vanilla should be #1076, Dark Sight, or with UAP's Race Mod, #1083, Malek. After the last bracket, hit enter a few times and add another entry:

{1084}{}

Then, in that second set of brackets, type the name for this background, then hit enter twice, like so:

{1084}{Sexy Ninja

}

Like in the above descriptions, write out a summary of your background. You can simply describe what has happened to them, or you can detail the stat and skill changes (we'll be getting to that next) that will be applied when the background is chosen. The double line break isn't strictly necessary, but it ensures none of the description is accidentally shown in the name.
After you are satisfied with your description, we can move on to the effects this background will have on the character.

Effect.MES

This next file may give you a bit of a headache to look at, but effect.mes is arguably the most fun MES file, as it contains all the buffs, curses, and stat modifications that can be summed up without the usage of scripting. Likewise, it also contains the effect data for the backgrounds.

Like in gameback.mes, scroll all the way down to the bottom and make a new set of brackets:

{365}{}

Inside those brackets, think of the stat modifications you'd like your background to impose on the character. Stats? Skills? Increased experience gain? Do you want everyone you meet to instantly hate you? Or perhaps you just want to max out your magickal/technological affinity? All of this and more is possible, but for now, lets keep it simple. Stat modifications use the same abbreviation as the character sheet window, so they should look something like this:

{365}{be +5, dx +4, ch +4, st +2, cn +1}

Here I have added the following:
+5 Beauty
+4 Dexterity
+4 Charisma
+2 Strength
+1 Constitution

The syntax is very important here. A space or comma in the wrong place could cause the effect to be skipped, or the entire background to not show up in the creation menu. I have yet to experience any crashes because of it, but going through and painstakingly looking for a single tiny error just isn't worth our time.

Keep in mind that you can only add 12 points to any stat, both within the game and from background effects. Only race modifiers and buffs/blessings can push it further than the base 20.
It's also worth noting that, just as it says at the top of the file, only five of each 'category' of effects can be applied. The categories, as I've been able to figure out, are as follows (there may be others, but it requires extensive testing to figure out, since many of the more advanced effects, like XP gain, aren't spelled out anywhere in the game):

• Stats
  
• Skills
  
• 'Derived Stats' (carry weight, etc)
  
• Miscellaneous/game effects (XP rate, etc.)

So I'm sorry to say you cannot max out every single stat and skill from the outset. I also should warn you that the categories are not clear. I've experienced some things that are listed in Derived Stats, but that are counted among the Misc. category, and things that aren't listed that are counted under Derived.

Continuing on, let's add some skills to the mix:

{365}{be +5, dx +4, ch +4, st +2, cn +1, prowling +8, armtrap +4, spottrap +4, melee +8, dodge +8}

Which is summed up as:
+2 Prowling
+1 Disarm Traps
+1 Spot Trap
+2 Melee
+2 Dodge

It's obvious there is a difference here, mainly that the skills seem to be 4x the actual amount. This is because, when you put a level-up point into a skill, it raises that skill by 4 points. You'll notice in the default backgrounds that raise skills, when they only add one or two, it shows as a tiny, useless sliver. I'm not sure if this is intentional, but it seems to be unbalanced as far as the game goes, so I've always done multiples of 4. Like the stats, the maximum is 20, and if you provide a negative amount (as some of the magick-centric backgrounds do), you cannot raise it to 20 in the game, as you can only put five points into any one skill.

Another thing you may have noticed about the skills is that some of the names aren't the same. Disarm Traps and Pick Locks go by slightly different names. Refer to other entries in the file to see how they are spelled (and to see examples not explained here).

Lastly, let's add some other effects to really bring a unique feel to the background:

{365}{be +5, dx +4, ch +4, st +2, cn +1, sneak +8, armtrap +4, spottrap +4, melee +8, dodge +8, xpgain +30%, reaction min 70, badreactionadj *0, healrate +50%} //Sexy Ninja 1084

With that, I've added the following:

• 30% increase to all experience gain
  
• All reactions to creatures and people not forced into combat will be a minimum of 70 (which is 'courteous'). This may have an unintended effect on the game, as some enemies might not enter combat with you when they should. Some scripts may also override this effect, causing enemies to hate you or like you regardless of the limits you've set here. Keep in mind that any reaction that dips to 0 or below will cause that entity to enter combat with you no matter what.
  
• All negative reaction adjustments (such as insults in dialog, or disreputable actions) will be multiplied by 0, effectively negating them (though this may not prevent them from entering combat if a script calls for it).
  
• Natural healing rate is increased by 50% - this includes both Health and Fatigue, though Health is way slower by default. (The total healing rate is listed under Derived Stats, and represents Fatigue/10s)

Here we see more advanced application of the effects- things like min and max, multiplication, and percentages. Many of these can be applied to all the other stuff too, like stats, skills, even the magick/tech aptitudes. The results are still bound by the game's hard-coded maximum for each adjustment, but it opens up a lot of possibilities.

Also note that I added a //comment at the end, with the background's ID and name. I recommend this for all the effects you add, just to make this file easier to read, especially when dealing with the backgrounds.
Now that we've got our effects lined up, we can start assembling the background for the game to process.

Backgrnd.MES

This last file is where the game actually looks when lining up the backgrounds to display during character creation. Here in backgrnd.mes, we will assemble all the pieces from the other three files into something you can use in the actual game.
They did a good job describing the format in the file itself, so I shouldn't need to go into too much detail.

Let's start by lining up the pieces we have. Note the following from the previous sections:

• The ID from gameback.mes
  
• The effect ID from effect.mes

Now note that the first set of brackets is offset by 10 for every new background, and unlike the other files, you can't skip any- they must be numbered consecutively. The last vanilla one was in the 780s, and the last Race Mod one was the 850s, so ours should use either 790 or 860, respectively:

{860}{1084} //Sexy Ninja
{861}{365}
{862}{}
{863}{}
{864}{}

Which covers the first two lines. The third, {##2}, is the race/gender combination for which this background will be visible. List all the race/gender combinations you want this background to be selectable for, separating them with spaces. Leaving it blank or putting "ANY" makes it available to all race/gender combos. The other possible combos are listed at the top of the file, usually two letters for the race and a third for the gender:

{860}{1084} //Sexy Ninja
{861}{365}
{862}{HGM HAM}
{863}{}
{864}{}

An excellent application for this is if you want to give different races/genders different equipment, such as Ogres large armor, or elves magickal items intead of technological ones. You'll have to create multiple entries in this file, but you can re-use the gameback.mes and effect.mes IDs.

The fourth line is the amount of starting money. It's just the amount; you don't need to do anything special for it. But the last line will be the items the game gives you at the start. This is where the description.mes file I had you open earlier comes in handy. Scroll down to the items you want, and copy the ID into the last line, again separating multiple items with spaces:

{860}{1084} //Sexy Ninja
{861}{365}
{862}{HGM}
{863}{1000}
{864}{8087 6121 6168} //Lg. Oiled Leather, Finely-Crafted Dagger, Serrated Chakram

After you've finished that, it's ready for testing!
A warning though, the ID numbers in MES files are a bit fickle. If you create so many backgrounds that you start to number them in the {1000}s, the game may not recognize them (it may even crash). My guess is it causes overlap with either description.mes or gameback.mes. The other files have limits too, but the exact number varies and I don't know the limit for each one off-hand. It's just something to keep in mind for troubleshooting.

Testing and Troubleshooting

The last step is to test your background. Assuming you followed my examples to the letter, you should be able to find the background under the correct race/gender combination you specified in backgrnd.mes, as the last entry (simply click the left arrow from 'No Background'):
Take the time to confirm that all the stats, skills, and effects have been properly applied/represented, and make adjustments to the effect.mes entry as necessary. Note that editing the files while the game is running may cause it to crash upon changing menus.

If you cannot find the background, I would check backgrnd.mes first to ensure the proper race/gender combo was applied, and effect.mes second for syntax errors. Triple-check that the IDs are all correct and in the correct place, and ensure that the numbering in backgrnd.mes is correct. Remember to check that the ID numbers in all files are correctly counting from the last entry. If you're using a mod that changed those files, they might not be the same as my examples.

If you notice some effects aren't being applied, check to make sure you didn't exceed the limit of 5, and that you spelled the entries in effect.mes properly; the game will only recognize the first five in a given category, and may ignore everything following a misspelling. If you want to test where a problem might be, move one of the modifiers from the same category after other entries and see if it applies. If it does, the problem lies after it.

Once you've confirmed all the effects have applied correctly, move on to the inventory screen to make sure your gold and items are there.
This one should be pretty easy. If it's not the right item, or the item is missing, it can pretty much only be a problem with what you put in that last line in backgrnd.mes. Triple-check that the ID numbers match and that they're spaced properly. If you're still not seeing an item, or the game is crashing upon reaching that screen, try different items. Some items were cut from the game and you may have chosen an invalid description.mes entry.

If you're having weird, unrelated issues, such as with graphics, dialog, or a part of another mod or tool you're using isn't functioning properly, it might be that the extracted files have overwritten theirs. In that case, you will need a fresh install, and re-install UAP and anything else you were using, then return to the DAT Files section and extract everything to a separate folder. Only copy the files over that you're modifying (making sure to put them in the right place), and remember not to overwrite existing files.

After all looks good at this point, your final test is the gameplay. Until you've confirmed it works, don't waste time creating a perfect character with your background; just do something quick to test it.
In my examples, I added an effect that caused all creatures to have a minimum 70 reaction to my character. Things like that can only be tested in the game:
After it passes this final test, you should be good to go!

Finally

Barring unforseen problems, you should have just created your first functional arcanum mod, and a brand new background for your character! It only gets better from here, as you learn to modify DLG, ART, and PROTO files. There's even an official world editor, though the Steam version doesn't seem to include it (it is a bit buggy).
I'm not sure when or if I'll get around to discussing those, but I do have the tools I used to use for them. If you're interested, let me know, and I'll dig up the download or just upload my copy. I hope this guide has helped you, and if you have any suggestions or questions, leave them in the comments for me to address.

Lastly, thanks to Cygone and David.Burnside.ZF for making me realize the UAP contained some potentially.... complicating features.

[Anubis 1101]

Yea some mods will already extract it, that's why I have you check first to see if the files are there before extracting them.

[Coffeepyromaniac]

If anyone doesn't want to (or isn't comfortable doing it) extract the DAT-files, there's a relatively simple workaround: if you're using the multiverse edition patch (I'd assume the UAP too, since it contains that, but the ME version is what I'm using and can confirm to work), it should have already done the extraction of gameback.mes, effect.mes and backgrnd.mes for you. As for the description.mes, you don't need to extract it. This https://arcanum.fandom.com/wiki/Description.mes website has a list of all the item codes.
Other than that, thanks for the tutorial.

[Anubis 1101]

That's definitely curious. It'd be neat if Drog removed that limitation, intentionally or otherwise.
Might have to check the patch notes and do some testing myself.

[Mighty Mangler of Bork]

So weirdly I got the game to accept more than 5 stat changes per category, or at least I got it to accept the main stats, but only on the newest UAP version, the multiverse edition repack which should have the newest UAP in it doesn't accept more than 5, I'm wondering if there's some change somewhere they missed or what, anyway it's very curious behaviour.

[Anubis 1101]

I'll keep trying different things on my end to fix the broken DATbuilder link, so keep telling me in the comments if it's not working.

[Anubis 1101]

I've suspected the link was broken, but I'm not getting much feedback. I'm trying to figure out how to fix it, but at this point I think I'll have to host it elsewhere.

Dunno why Google randomly decided to break everything like that. I've read all the documentation about the update that broke it, and there's nothing helpful at all.

[Kashenkon]

I love your guide Anubis 1101! You won three prices.

This was help me much out, to create a background for an elf, what i planned to a technological playtrough. And this work very well.

The download links of the DATBuilder doesnt work.
I was found one on Terra Arcanum website.

[Anubis 1101]

try it now, should be fine.
google updated their security features for files on the Drive so of course it broke everything.

[xelzega]

Is the datbuilder file download not working anymore?

[Zalehov9]

Noticed in the changelog of Drog Black Tooth's UAP that he had some key bindings changed or added, curious to know how he managed that but couldn't see anything in arcanum5.dat related to keyboard characters. In the meantime I'll look into the autohotkey programs again, thx.