Checksum

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Checksum location

A checksum is a means by which a computer confirms the contents of a file. If, when the computer runs the checksum test over the file, it comes to a different checksum value than what is suspected, it lets the computer know that the file is modified in some way from what is expected. (Such mismatches in a checksum could be due to corruption of the file or even computer viruses.)

In the case of EU4, Paradox uses checksums to let players know their games have been installed correctly, and also as a way to ensure players are using compatible versions when playing in multiplayer games.

Finding the checksum[edit]

The checksum will appear in the lower left corner of the main screen next to the version number. For instance, the EU4 manual shows an example of "EU4 v1.00b (ce94)". The version is "v1.00b". The checksum is "ce94."

Usage in installation[edit]

Players can check the checksum to ensure their games were installed correctly. If, after launching the game, a different checksum is shown compared to what is expected, the player knows that their copy of the game may be missing key components or is corrupted in some way. The player may need to reinstall the game in order to achieve the correct checksum.

Use in multiplayer[edit]

Players using the multiplayer game features need to compare their games to make sure that all players share the same checksum. If any of the players have a different checksum, their games are incompatible and the multiplayer game cannot be started.

The quickest way to verify that you are both using a compatible version is to consult the “checksum,” that four letter code following the version number at the bottom left of the main screen. In the picture here, the checksum is ce94. If your opponent’s checksum matches yours, then you are ready to play. Note that a checksum of XXXX indicates you have entered single player and backed out to main menu. To resolve this, you must exit and restart the game before attempting to play multiplayer. — EU4 Manual, page 17.

Use in 'Ironman' mode[edit]

See also: Ironman

Nowadays it's possible to play a game in Ironman mode even though your checksum isn't identical to any of the official game versions' (for example because you play the game with one or several mods that change the checksum). This was different in the past [when?]. However, if you want to get achievements you need to not only play in Ironman mode, but also have the checksum that's the correct one for your version of the game.

What affects the checksum?[edit]

The checksum is created by EU4 looking at certain files in its file-structure, and generating a unique key for the contents of those files. However, some files and folders are ignored by the checksum generator, which allows us to tinker with certain aspects of the game in mods, via the mod folder system.

Following files are used for the checksum calculation:

  • common:
    • including sub directories
    • all .txt and .lua files
  • events:
    • including sub directories
    • all .txt files
  • missions:
    • including sub directories
    • all .txt files
  • decisions
    • including sub directories
    • all .txt files
  • history:
    • including sub directories
    • all .txt files
  • map:
    • all .txt, .map,.csv and .bmp files
    • all .lua files in map/random
Modding
Information ChecksumCommandsConditionsConsole commandsJoroDox mod making toolMod structureScopesThe Validator
Guides AdvisorsCasus belliColonial regionsCountry creationCultureDecisionsDefinesDisastersEventsFactionsGovernmentIdea groupsLocalisationThe mapMissionsModifiersMusicPoliciesReligionScenarioTechnologyUnit models