Skip to content
A mod list downloader & installer for Skyrim/Oblivion and Fallout games
Branch: master
Clone or download
Latest commit daeaeb5 Sep 18, 2019

Wabbajack - An automated modlist installer for TES/Fallout games

The general idea behind this program is fairly simple. Given a Mod Organizer 2 folder and profile, generate list of instructions that will allow a program to automatically recreate the contents of the folder on another machine. Think of it as replication, but without ever distributing copyrighted files or syncing data between the source and destination machine. The end result is a program that recreate a modlist on a computer while respecting the rights of the game publisher and the mod authors.

Social Links

What Wabbajack can do

At this point you may be wondering how much of a complex modlist Wabbajack can handle. At this point it's more about what Wabbajack can't handle, but let's do a rundown of all the supported features:

  • Support for the following games is tested on a regular basis
    • Fallout 4
    • Fallout New Vegas
    • Skyrim SE
    • Skyrim LE
  • Support for automatic downloads from the following sources
    • Nexus Mods (Premium accounts only)
    • Dropbox
    • Google Drive
    • Mega
    • ModDB
    • Direct URLs (with custom header support)
  • Support the following archive types
    • .zip
    • .7z
    • .rar
  • The following mod installation types are supported
    • Files installed with our without fomod isntallers
    • Manually installed mods
    • Renamed/deleted/moved files are detected and handled
    • Multiple mods installed into the same mod folder
    • A mod split across multiple mod folders
    • Any tools installed in the MO2 folder. Want your users to have BethIni or xEdit? Just put them in a folder inside the MO2 install folder
    • ENBseries files that exist in the game folder
    • SKSE install
  • The following situations are automatically detected and handled by the automated binary patcher (not an exhaustive list)
    • ESP cleaning
    • form 44 conversion
    • ESP to ESL conversion
    • Adding masters
    • Dummy ESPs created by CAO
    • (really any ESP modifications are handled)
    • Mesh fixing
    • Texture compression / fixing The following BSA operations are detected by extracting or creating BSAs via Wabbajack's custom BSA routines
    • BSA Unpacking
    • BSA Creation (packing loose files)
    • BSA repacking (unpacking, fixing files and repacking)

That being said, there are some cases where we would need to do a bit more work to develop:

  • Manually downloaded files
  • LL Files (currently no plans to implement)
  • esp to esm conversion (there are hacks for this)
  • binary patching of non-bsa huge files. 256MB is the largest size Wabbajack can currently handle with the binary patcher

Creating a ModList Installer

Overview video []

  1. Download Wabbajack and install it somewhere outside of your normal Mod Organizer 2 folder (otherwise Wabbajack will try to figure out how to install itself and that might cuase a collapse in the time-space continuum).
  2. Make sure every archive you used in your MO2 profile has some sort of download information attached.
    • If the file was downloaded via MO2 you're good, no extra work is needed
    • If the file was downloaded manually from the Nexus, copy it into the MO2 downloads folder, go back to MO2
    • and go to the downloads tab. Find the file and click Query Info from the right-click menu. MO2 should find the download info for you
    • For other files (ENBSeries, SKSE, SRO, etc.) Look at the file
    • for instructions specific to your file source.
  3. Now load Wabbajack, and point it to the \<MO2 Folder>\mods\<your profile>\modlist.txt file.
  4. Click Begin.
  5. Wabbajack will start by indexing all your downloaded archives. This will take some time on most machines as the application has to performa SHA-256 hash on every file in every archive. However the results of this operation are cached, so you'll only need to do this once for every downloaded file.
  6. Once completed, Wabbajack will collect the files required for the modlist install and begin running them through the compilation stack.
  7. If all goes well, you should see a new <your profile name>.exe file next to Wabbajack.exe that you just ran. This new .exe is the one you want to hand out as a auto modlist installer.

Installing a ModList

  1. Get a modlist installer, it's a .exe file that was created by Wabbajack
  2. Run the .exe, the install folder defaults to the same folder as the executable, change it if you want.
  3. Click Begin to start installation. At some point you will be prompted for SSO authorization on the Nexus, files will be auto installed and downloaded
  4. After installation has completed, run Mod Organizer 2.exe, select Portable and your game type.

How it works

At a technical level the process is as follows.

  1. Hash and cache the contents of every archive in the \downloads folder. This lets Wabbajack know of all the possible locations where you could have installed mods
  2. Apply the resolution stack to every file in both the game's root folder and in the MO2 folder.
  3. Take the install directives and required archives and write their metadata to a JSON file.
  4. Attach the JSON file to Wabbajack itself, creating a new Auto-installer for the profile

The Resolution Stack

Every file analyzed by Wabbajack is passed through a stack of rules. The first rule to match the file creates a Install Directive or a instruction on how to install that specific file.

Currently the Resolution stack looks like this:

  1. Ignore the contents of logs\
  2. Directly include .meta files int the downloads\ folder
  3. Ignore the contents of downloads\
  4. Ignore the contents of webcache\
  5. Ignore the contents of overwrite\
  6. Ignore any files with temporary_logs as a folder in the path
  7. Ignore .pyc files
  8. Ignore .log files
  9. Ignore any files in profiles that are not for the selected MO2 profile
  10. Ignore any disabled mods
  11. Include any profile settings for the selected profile by including them directly in the modlist
  12. Ignore "ModOrganizer.ini", it will be re-created when MO2 starts on the new machine
  13. Ignore "Data" in the Game directly (in your Steam folder)
  14. Ignore "Papyrus Compiler" in the game folder
  15. Ignore the "Skyrim" folder in the game folder
  16. Ignore any BSAs in the game folder
  17. Include all meta.ini files from all (selected) mods
  18. Include archive and file meta information for any file that matches a file in an archive directly via a SHA256 comparison
  19. Rip apart any .bsa files and run a mini resolution stack on the contents to figure out how to build the .bsa from the input files
  20. Generate patches for files that may have been modified after being installed from an archive (see section on Patching for more info)
  21. Include dummy ESPs directly into the modlist
  22. Ignore files in the game directory
  23. Ignore .ini files
  24. Ignore .html files (normally these are logs)
  25. Ignore .txt files
  26. Ignore HavockBehaviourPostProcess.exe this seems to get copied around by tools for some reason
  27. Ignore splash.png it's created for some games (like FO4) by MO2
  28. Error for any file that survives to this point.

So as you can see we handle a lot of possible install situations. See the section on Creating a Modpack for information on working with the installer

Wabbajack Flags

The if the following words are found in a mod's notes or comments they trigger special behavior in Wabbajack.

  • WABBAJACK_INCLUDE - All the files int he mod will be inlined into the installer
  • WABBAJAC_ALWAYS_ENABLE - The mod's files will be considered by the compiler even if the mod is disabled in the profile


Wabbajack can create binary patches for files that have been modified after installation. This could be .esp files that have been cleaned or patched. Or it could be meshes and textures that have been optimized to work better in a given game. In any case a BSDiff file is generated. The output of this process is copied directly into the modlist instructions. However! It is important to note that the patch file is 100% useless without the source file. So original + patch = final_file. Without the original file, the final file cannot be recrated. This allows us to distribute arbitrary changes without violating copyrights as we do not copy copyrighted material. Instead we copy instructions on how to modify the copyrighted material.


How do I get Wabbjack to handle mods from X

Look at the file, we keep a knowledgebase of how to deal with given types of mods in that file.

Why does each modlist install another copy of Mod Organizer 2?

Self-contained folders are a cleaner abstraction than dumping tons of modlists into the same set of folders. It's easy to uninstall a modlist (simply delete the folder), and MO2 really isn't designed to support lots of disparate modlists. For example if two modlists both wanted a given texture mod, but different options they would somehow have to keep the names of their mods separate. MO2 isn't that big of an app, so there's really no reason not to install a new copy for each modlist.

Why don't I see any mods when I open Mod Organizer 2 after install?

Make sure you selected the "Portable" mode when starting MO2 for the first time. In addition, make sure you haven't installed MO2 in a non-portable way on the same box. Really, always use "Portable Mode" it's cleaner and there really isn't a reason not too do so. Make the data self-contained. It's cleaner that way.

Will Wabbajack ever support Vortex/other mod managers?

I'll be honest, I don't use anything but MO2, so I probably won't write the code. If someone were to write a patch for the functionality I wouldn't throw away the code, but it would have to be done in a way that was relatively seamless for users. Since Wabbajack treats all files in the same way it doesn't know what mod manager a user is using. This means that if the modlist creator used Vortex all users of the modlist would have to use Vortex. This doesn't seem optimal. It's possible perhaps, but it's at the bottom of the priority list.

Where is the modlist? Why am I just given an .exe?

When Wabbajack creates a modlist, as a final step it copies itself (the wabbajack.exe) and tacks onto the end of the file the modlist data, and a few bits of magic text. When Wabbajack starts it looks at itself to see if it has this extra data tacked on to the end of the executable. If the data is found the app kicks into installation mode. This means that Wabbajack acts a lot like a self-extracting installer.

Do you know that some mod authors don't like their mods being automatically installed?

Yes, I've heard this, but they chose to host their data on a public site. And no, they don't have the right to dictate what HTTP client is used to download a file. We're using official Nexus APIs for nexus downloads, so any downloads Wabbajack performs are correctly tracked, and MO2 encourages users to endorse mods. It's 2019, we can have better tools than manually clicking links.

How does Wabbajack differ from Automaton?

I (halgari) used to be a developer working on Automaton. Sadly development was moving a bit too slowly for my liking, and I realized that a complete rewrite would allow the implementation of some really nice features (like BSA packing). As such I made the decision to strike out on my own and make an app that worked first, and then make it pretty. The end result is an app with a ton of features, and a less than professional UI. But that's my motto when coding "make it work, then make it pretty".

Thanks to

Our tester and Discord members who encourage development and help test the builds.

Patreon Supporters

Daedra level Patreon Supporters

  • Ancalgon

Patreon Supporters

  • Druwski

License & Copyright

All original code in Wabbajack is given freely via the GPL3 license. Parts of Wabbajack use libraries that carry their own Open Sources licenses, those parts retain their original copyrights. Note: Wabbajack installers contain code from Wabbajack. Therefore, selling of modlist files is strictly forbidden. As is hosting the files behind any sort of paywall. You recieved this tool free of charge, respect this by giving freely as you were given.

You can’t perform that action at this time.