Mod structure

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Mod File Structure[edit | edit source]

Local Mod[edit | edit source]

Local Mod files must be located in the folder ~/.local/share/Paradox Interactive/Hearts of Iron IV/mod or C:\Users\<Username>\Documents\Paradox Interactive\Hearts of Iron IV\mod, which must contain:

  • The '.mod' file, to tell the launcher what to do with the mod-folder (For local use only, any name possible; this file does not get uploaded, when publishing the mod via Steam Workshop)
  • The mod folder or zip containing the mod data. The mod data must have the same file and folder structure as the game's directory itself.
  • descriptor.mod file inside the mod folder - this file should contain the same information as the first .mod file (Note: The File must use the descriptor.mod name and must NOT be saved in UTF-8 BOM format)
  • Mod picture (optional) - a file named thumbnail.png in the mod folder, to serve as Steam Workshop mod picture (Note: Must use .png format and 'thumbnail.png' name; dimensions aren't important but should be 1:1 ratio)

The game launcher's mod config tool can create basic structure automatically. Just go to Mods tab, then click Mod Tools and Create Mod. Note that folder and file names are case sensitive on Mac OS X and Linux.

Steam Workshop Mods[edit | edit source]

Subscribed and downloaded mods from the steam workshop are in .../Paradox Interactive/Hearts of Iron IV/workshop/content/394360 or sometimes ...\SteamLibrary\steamapps\workshop\content\394360

Mods downloaded from the Steam Workshop are treated differently than those manually installed or created:
Though the mods .mod files will appear in the mod folder (represented by a remote_file_id), The content of the mod will be stored in ...\Paradox\Hearts of Iron IV\workshop\content\394360\<remote_file_id>
The remote_file_id is an ID given to mods from the workshop. The ID is displayed as the name of the mod's .mod and zip files, but is further represented within the .mod and descriptor.mod files as such:

name="New Ideologies"

Note: Newer mods, starting with game version 1.9.0 are no longer stored in a .zip archive

Creating a New Mod[edit | edit source]

General rules[edit | edit source]

  • Mods modify the game with the same file structure as in the vanilla game.
  • All appropriate files found in the folder are loaded
  • All .txt files should use UTF-8 without BOM format, Localisation files should use UTF-8 BOM Format
  • To overwrite the vanilla file, use the same file name
  • To add content without changing any vanilla files, use a different file name
  • The Game will not check any further than the file directory for changes. If one is trying to add a line to a text file, one must copy the entire text file and add the line within said text file.

Creating a simple local mod[edit | edit source]

For example, to create a mod called "Test1", create a new text file called test1.mod and a folder named 'test1' within ...\Paradox\Hearts of Iron IV\mod.

The contents of test1.mod should be as follows:

	"Alternative History"

This is done to provide the game launcher with information about the mod. This includes the mod's name, location (from the mod file), tags (extra descriptors), picture name, and supported game version.

Creating a Submod[edit | edit source]

Sometimes you will want your mod to depend on other mods, and also require a certain loading order. Mods will usually load in alphabetical order (so the mod last in the list will overwrite the earlier). But some things may affect this so if you need a certain load order and be clear that you have dependencies this needs to be specified by including its full name in the .mod file under "dependencies".


# this guarantees we load testmodA first before our testmodB is loaded
dependencies= { 

Adding Mod Content[edit | edit source]

For example, a simple modification could be changing the text that appears in the game.

To change the quotes that appear in the loading screen, copy the "localisation/loading_tips_I_english.yml" file from the base install of the game, ".../Hearts of Iron IV/localisation/loading_tips_I_english.yml" to a "localisation" folder you create in the new "mod/test1" folder.

The file structure now looks like the following:

 ...\Paradox Interactive\Hearts of Iron IV\mod
     test1 (dir)
       localisation (dir)

As "loading_tips_I_english.yml" is unaltered, the game will run the same as usual. However, if it is changed, the information will be used by the game instead of the usual "loading_tips_I_english.yml". Modify the "loading_tips_I_english.yml" file in the mod folder so that it contains this:

  LOADING_TIP_0:0 "Test1 mod"

When the game is loading with this mod active in the English language, the only quote shown will be "Test1 mod".

Tips[edit | edit source]

  • To understand how certain things in the code work, it can be useful to look into game files and search for things similar to what your mod is supposed to change
  • Alternatively, you can search the files of other users' mods in ...\steamapps\workshop\content\394360
  • Try to minimize vanilla file overwrites, this will make it both easier for you to manage your mod content to keep it up to date and reduce risk of conflict with other mods
  • When testing the mod, it can be very useful to look into Error log ...\Documents\Paradox Interactive\Hearts of Iron IV\logs\error.log to gain a clue when something isn't working
  • To keep your mod updated between smaller updates, replace the third number in your version with a *. For example, replace "1.5.4" with "1.5.*" to make that mod work with all versions of 1.5

See also[edit | edit source]

Depending on what your mod is supposed to do, you may want to visit some of these pages relating to some more basic game content modding: