Mod structure

To create a mod for Europa Universalis IV, you need to replicate the directory structure of the files which will be altered, then create a .mod file which tells the launcher the location of the new files.

.mod file

Where this file goes depends on the platform:

• Windows: Documents\Paradox Interactive\Europa Universalis IV\mod
• Linux: ~/.local/share/Paradox Interactive/Europa Universalis IV/mod
• Mac OS: ~/Documents/Paradox Interactive/Europa Universalis IV/mod

It simply tells the launcher the directory it should look in, the name it should display to the user, and (as of Patch 1.8) the supported version of Europa Universalis IV. For example:

name = "My Mod version 3"
path = "mod/mymod_v3"
supported_version = "1.9"

The supported version must match the major version number of Europa Universalis IV (1.8, 1.9, etc.) being used by the launcher in order to be loaded into the game.

When uploading it to the Steam workshop include a picture and tags so it is more easily found while browsing, like so:

name = "My Mod version 3"
path = "mod/mymod_v3"
supported_version = "1.9"
picture = "mymod_picture.jpg"
tags = {
 "Events"
 "Historical"
}

The picture file should go inside the "mymod_v3" folder rather than the Europe Universalis IV\mod directory.

Since the launcher updated with patch 1.29, the picture file should be named "thumbnail.png" and needs to be a decently small size, assumed to be 1 MB or smaller.

Steam tags

The tags are the tags in use in Steam's system.

Currently any combination of the following works:

• Alternative History
• Balance
• Events
• Expansion
• Fixes
• Gameplay
• Graphics
• Guide
• Historical
• Loading Screen
• Map
• Military
• Missions And Decisions
• National Ideas
• New Nations
• Religion
• Sound
• Technologies
• Trade
• Translation
• Utilities

General notes

• Audio file format

  As far as known, only OGG files will correctly play. While the engine doesn't crash or throw errors, it will not play MP3 files. Executing 'nextsong' in the console will print the console message "playing music/foo.mp3", suggesting that the file is read, but not actually played.

Mod folder

This folder goes in the same place as the .mod file. It should have the same directory structure as the contents of the Europa Universalis IV folder, minus the unchanged files. The game will load files from the root Europa Universalis IV folder, but if it encounters a different version of a file in the mod folder, it will load that instead.

This folder should also contain a "descriptor.mod" file that contains all the same information as your initial .mod file, but doesn't need to contain the "path = " line.

However, if to completely change a folder - for instance removing all missions from the game - add replace_path = "missions" in the .mod file. Any game folder that is added with this command will simply not be loaded.

name = "coolmod"
path = "mod/coolmod"
supported_version = "1.9"
replace_path = "missions"

Important: if to replace a folder with an empty folder - making sure nothing of that content is loaded - place a dummy file in the folder. Otherwise the empty folder in the mod won't be included when uploaded to Steam. [2]

Submod

Eu4 loads the mods in alphabetical order and does not honor the load order of mods in the launcher. To make a submod which overrides files of a primary mod, a dependencies section can be added to the .mod file:

name = "othercoolmod"
path = "mod/othercoolmod"
dependencies={
        "My Mod version 3"
        "coolmod"
}

This mod will override the files of both "My Mod version 3" and "coolmod".

Uploading The Mod

In the new Paradox Launcher, you should be able to quickly upload your mod to either the Paradox Mods service or Steam Workshop. From "All Installed Mods", there is an "Upload Mod" button where you should be able to select the mod you have been working on. If it's not visible, make sure you have a folder which contains only the mod files (eg. /common/tradenodes) and a file called 'descriptor.mod'. Also, make sure you have a .mod file in the ...\Europa Universalis IV\mod\ folder with a "path =" line pointing towards your mod folder.

What is in each folder

common

advisortypes

Defines the different types of advisors which can be hired: their traits, associated monarch power, and what modifies the chance of getting one.

ai_attitudes

Defines the attitudes AI countries can have to the player and each other, such as Neutral, Friendly, Hostile, Protective, etc., along with what modulates the chances of having these attitudes.

ai_personalities

Defines the overall "personalities" that AI countries can have, such as Administrator, Militarist, Diplomat, etc. There isn't much that you can change in here; it's practically hardcoded.

bookmarks

Defines the bookmarked dates that appear in the scenario selection screen, along with the suggested countries to play.

buildings

Specifies what buildings can be built and their associated costs and benefits.

cb_types

Defines the Casus Bellis (CBs) a nation may use to declare war. It is important to note that wargoals are not defined in this file, and that incorrectly defining either may cause strange bugs.

church_aspects

Defines Protestant church aspects and benefits of them and blessings for Coptic nations.

client_states

Defines the preset client states which a nation may create upon reaching technology level 22.

colonial_regions

Defines the areas where colonial nations may spawn in. You need 5 provinces in a colonial region to spawn a colonial nation.

countries

Contains a list of text files describing some of the properties all countries, such as their historical idea groups, ruler names, leader names, ship names, their color on the map, and so on.

country_colors

Ordinarily the colors of a country's soldiers' uniforms are determined by the engine looking at the dominant colors of their flags. However, for certain countries it is sometimes needed to override this.

country_tags

Defines a unique, 3 letter code, or "tag", for every single country, and points to the file in common\countries in which it is defined. It is important that every single tag defined herein has a corresponding file in common\countries, or else the game will crash at launch. Check to make sure it is spelled correctly.

cultures

Defines cultures and culture groups.

custom_country_colors

Defines colors that can be used by custom nations.

custom_ideas

Defines ideas that can be used by custom nations.

defines

Defines the bonuses to players and AIs with different difficulty levels.

diplomatic_actions

Defines diplomatic actions and requirements for completing them.

disasters

Defines disaster types, triggers, and modifiers.

dynasty_colors

Defines the colors of dynasties on the dynasty mapmode.

estates

Defines the estates that you can interact and give provinces to.

event_modifiers

Defines modifiers which may give bonuses or maluses to a country, which are activated by event. These can be for either provinces or countries. The duration of the modifier is not specified in here, but in the event which triggered it.

factions

Defines the factions used in Ming's Celestial Empire government, merchant republics, and revolutionary republics. It is possible to define new factions in here too, for other countries. This requires many other files to work in tandem. For more information see modding factions.

fervor

Defines use of fervor and related bonuses.

fetishist_cults

Defines the cults that you can choose from when playing as a Fetishist nation.

government_names

Defines the names that will appear in events and decisions depending on your government rank and type.

governments

Defines the different types of governments and under what conditions the AI will switch to them.

great_projects

Defines Great Projects and associated modifiers.

hre_reforms

Defines the reforms the Emperor can pass, from Reichsreform to Renovatio Imperii

ideas

Defines the ideas unlocked through spending points, as well as unique country (and group) National Ideas and Traditions.

institutions

Defines institutions, bonuses for supporting them, as well as their spawn province.

leader_personalities

Defines personality traits that generals and admirals may acquire after battles, and their associated bonuses.

native_advancement

Defines native ideas and other properties.

natives

Defines what type of natives live in different unoccupied provinces according to region, and their numbers, aggressiveness, and ferocity.

on_actions

These are triggers for events which fire when the game engine reaches certain conditions. These conditions do not seem to be documented well anywhere (though see this forum discussion) Some of these conditions are based on a game event like losing a siege, which can trigger event #9206, an event about tribal armies looting. Others are triggered via "pulses", as in "on_bi_yearly_pulse" which has a chance to trigger one of several events every two years.

opinion_modifiers

Defines the modifiers to countries' opinions of each other, and how long they last for.

parliament_bribes

Defines the required bribes for Parliament to increase the chances of passing legislation.

parliament_issues

Defines the issues that you can choose from in the Parliament menu.

personal_deities

Defines personal deities and associated bonuses for each for Hindu and Norse religions.

policies

Defines policies (acts) and associated modifiers granted by enabling each of them.

powerprojection

Defines fixed, dynamic, and ticking sources of power projection, their decay, and their maximums.

prices

Defines the prices of tradegoods, and what alters the demand for them.

province_names

Defines dynamic province names; used if setting is enabled.

rebel_types

Specifies the different types of rebels, what their demands are, when they spawn, how hard they fight, etc.

region_colors

Determines the color of each region in the region mode, not labeled.

religions

Defines the different religions ingame along with their associated heresies, province and country bonuses, what they call their wars, and so on. More more information see religion modding

religious_reforms

Defines religious reforms for the Nahuatl, Inti, and Mayan religions.

revolt_triggers

Determines if a country will become independent from rebels.

ruler_personalities

Defines various ruler personalities, their effects, modifiers to chances of developing, and costs for custom nations.

scripted_effects

Scripted effects.

scripted_functions

Scripted functions.

scripted_triggers

Scripted triggers.

static_modifiers

Defines the effects of a large number of effects that don't change, such as prestige, legitimacy, and war exhaustion.

technologies

Specifies the different tech levels according to what monarch power is used for them.

trade_companies

Defines provinces required, naming, and colors of trade companies.

tradegoods

Defines tradegoods and what effects come from controlling their trade.

tradenodes

Defines which provinces are in what tradenodes, and how the nodes connect to each other.

triggered_modifiers

Defines things like the "Conquest of Mecca" modifier which hold constant so long as certain conditions are met.

units

Defines the stats and tech group of land and naval units.

wargoal_types

Defines wargoals for Casus Bellis (i.e. what can be taken in peace deals and what causes the ticking warscore)

achievements.txt

Defines achievements.

alerts.txt

This file holds your message settings.

defines.lua

Miscellaneous things. Searching this file can be useful for finding a number of settings.

graphicalculturetype.txt

Defines graphical culture types.

historical_lucky.txt

Defines lucky nations.

technology.txt

Defines tech groups.

decisions

These .txt files define the decisions a country can take, including its preconditions, effects and what determines whether the AI will pick it.

events

These files define events that can happen to players or AI countries: what triggers them, how often they happen, and their options and effects.

gfx

Contains the art assets used ingame. Most germane for modding are the flags and event_pictures folders.

history

advisors

Defines historical advisors (Machiavelli, da Vinci, Newton, etc.)

countries

Files in here define the history of every country in the game. The filenames must begin with the country's tag. At a bare minimum they must contain the preferred government type, tech group, religion, culture and preferred capital. Optionally they may specify historical monarchs, regime changes, religious conversions and the like.

diplomacy

Define historical alliances, royal marriages, vassals, etc.

provinces

The history of every single province in the game is specified here. Who owned it, the base tax, who had discovered it, the religion, trade goods, etc.

wars

Historical wars.

interface

These .gfx and .gui files define the structure of the interface, menus, and how the art assets are displayed.

localisation

Contains .yml files specifying what text is displayed ingame, optionally translated into other languages.

map

lakes

Contains the positions and elevations of lakes.

random

Base files for use in generating random new world map tiles

tiles

Files and images relating to new random new world tiles

terrain

Contains small image files specifying how things like the fog of war, border lines and so on look.

adjacencies.csv

Defines what provinces are connected to others via narrow straits that troops can walk across unless blockaded by an enemy.

ambient_object.txt

Tells the engine where to display flavor objects on the map, like bears and eagles and windmills and stuff.

area.txt/region.txt/superregion.txt

Defines the areas, regions and superregions for provinces

climate.txt

Defines the climates of provinces, like which ones get the attrition modifiers in winter.

continent.txt

Defines which provinces belong to which continent.

definition.csv

Defines each province by number and what RGB value they correspond to in provinces.bmp

heightmap.bmp

Grayscale image telling the engine how high each bit of the map should be elevated. Light is high, dark is low. Altering this does NOT alter whether provinces have terrain penalties during combat; that is specified in terrain.bmp.

minimap.base

The background of the minimap

positions.txt

The location of buildings and units in a province

provinces.bmp

The layout of the provinces, both land and sea, are defined here. Each province is a unique RGB color, which is specified in definition.csv. When editing this make sure to do so without antialiasing or blurred brush edges on.

region.txt

Specifies which provinces belong to what region.

rivers.bmp

The locations of the rivers in the game.

seasons.txt

Defines the start and end of the seasons and how the color filter on the map changes.

terrain.bmp

Specifies which areas of the map are mountainous, forest, etc. by color.

terrain.txt

Defines the penalties associated with terrain, and how they correspond to the colors in terrain.bmp

trade_winds.txt

Defines the trade winds for oceanic crossings

trees.bmp

Locations of different tree types

world_normal.bmp

It's a normalmap for the engine to handle lighting and speculars and stuff.

_canal_river.bmp

Shows the location of the canal named at the start of the file

missions

Defines missions for the player and the AI can attempt, including the requirements, conditions for winning and failure, and the reward.

References

Modding

Audio

Music • Sound