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About this mod

Mod Organizer (MO) is a tool for managing mod collections of arbitrary size. It is specifically designed for people who like to experiment with mods and thus need an easy and reliable way to install and uninstall them.

Permissions and credits

Mod Organizer v2.2.0 has been released, see the logs section for all the changes.
Mod Organizer 2 Full Changelog

For Wrye Bash to work with MO 2.2.0 you need to update Windows 10 to build 1809. You might have to use the Windows Update Assistant to get that done:

Mod Organizer 2 is a mod manager created by Tannin to support 64bit games like Skyrim Special Edition and Fallout 4 in addition to all the 32bit games MO1 already supported.
Tannin discontinued the project when he was hired by the Nexus team to develop their new Vortex mod manager.
MO2 was not completed and was left with many issues. LePresidente managed to fix it to a usable state by himself after SkyrimSE came out, adding support for it, and releasing v2.0.8.
The project took up speed again after a few more coders showed up in late 2017, and an incredible amount of work has been done!

Credits to Tannin, LePresidente, Silarn, erasmux, AL12, LostDragonist, AnyOldName3 and many others for the development.

A Special Thanks to all the testers of the discord server and everyone else involved for supporting the project!

MO2 Team:

For a list of currently known issues and general info please see the pinned posts.

Mod organizer 1 Legacy (thanks enpinion):
Recently Nexus changed their services to be compliant to the new EU rules. These changes required programs making use of them (such as MO1, NMM and MO2) to be updated to be able to still use Nexus integrations.
Even though MO1 is End of Life and will not get any future updates, enpinion managed to get the Mo1 code to build and has been able to fix this issue. We discussed with Tannin (original creator of MO1 and Mo2) and decided to host here the fixed Legacy version. This does not mean that Mo1 will receive any further updates, or that it is supported in any way. The Mo2 team will continue to work on Mo2 and strive to make it the better program.

Link to the Mo1 source code:
Mod Organizer 1 original page:

Mo1.3.15 changelog:

Credits go to enpinion for the fixes and Tannin for the program.

Mod Organizer 2 is an open project in the hands of the community, there are problems that need to be solved and things that could be added. MO2 really needs developers and if you have the programming skills and some free time you can really improve the experience of the modding community.

To have more information please join the open MO2 Development discord server : ModOrganizerDevs
You can find the MO2 code here:
It's subdivided into many repositories that can be found under the Modorganizer2 GiitHub organization repositories.
To build and setup a development environment on your machine of MO2 there is an umbrella project that handles it. Here are the instructions to setup a dev environment.
If you want to help translate MO2 to your language you should join the discord server too and head to the #translation channel.

Through the work of a few people of the community MO2 has come quite far, now it needs some more of those people to go further. (literally things will not get fixed if no one shows up to fix them)

MO2 survived because people spontaneously offered their help where they could, no one forces them to continue spending their limited free time on the project.
So nothing is to be expected, everything is to be thanked for. 

Mod Organizer (MO) is a tool for managing mod collections of arbitrary size. It is specifically designed for people who like to experiment with mods and thus need an easy and reliable way to install and uninstall them.

The special fact about MO2 is that it uses a Virtual File System (VFS) instead of actually installing your mods into the Data folder of the game.
MO2 uses it's VFS to trick the game and other programs into thinking that the mods are installed in the data folder while they are actually installed in their own separated folders. This VFS is called USVFS (User Space VFS), which is different from the VFS that MO1 used, since the old one did not support 64bit programs, but it works on a similar concept.
Which means that only programs started through MO2 will see the mods, while for the rest of the world the game will remain vanilla.

The VFS works by hooking the target program (and any of it's children processes), intercepting all the requests of accessing files and folders, if those are referred to the game Data folder then usvfs will intervene and change the answer so that it looks to the program like all the Mods files are located there as well (this kind of behavior is similar to how some types of malware behave and that is why some Antivirus will flag usvfs badly).
This system allows for a process specific virtual folder that does not take up space and can be interacted with without having to actually move or copy any files.

The implementation of usvfs is quite complex and low level as it goes and hooks Windows API calls, keeping a shared record across hooked process of the changes such as added files and deleted ones in real time.
Usvfs is a standalone library that is meant to be usable in different applications other than MO2, as such it does not contain MO specific code like the MO1 VFS did (hook.dll).

Differences with Mod Organizer 1:

MO1 and Mo2 can be considered different programs. The main difference between the two is that the virtual file system (vfs) used by Mo1 does did not support 64bit games. Because of this MO2 has a completely new vfs library (called usvfs) that was made to support 64bit programs as well. This library is more separate and independent from the rest of the program allowing for it to be potentially used even by other programs.

Another major difference is that Mo1 had a special system to manage Bethesda Archives (BSAs). 
Tannin (the creator of both MO1 and MO2) decided to not include this feature in MO2 for the fact that it subverted how the the game actually loaded the Archives causing problems with tools and mods that relied on the original system to work. That in addition to the sheer complexity of implementing the feature with the new virtualization library and making it work with all the supported games (the Mo1 system was based on a hack).
From his experience and all the problems he had with Mo1, Tannin came to the conclusion that using a special system for BSA management that did not follow what the game did was a mistake.
We agree on that fact, having seen the problems it caused and compromises that the feature would have required. 

We are working though in restoring BSA (and all other typs of Archives like BA2) parsing for conflict detection. This time it will follow the standard game rules, which are:
All Archives are loaded in the order of the plugins loading them (in Mo2 you can't disable dummy plugins), and after that all loose assets are loaded on top. So loose assets can't be overwritten by archives.
We are looking for the best ways to visually show the conflicts of BSAs as they don't follow left pane order anymore, but right pane instead.
We will be looking into ways to not use dummy plugins to load BSAs in the future.

MO2 is of course receiving active development from the community while Mo1 does not, which means that there are and will be new features in MO2.
Listing everything here would be too long so to have a better idea of all the things that Mo2 adds you are invited to read the Changelogs that you can find under the LOGS tab.

Here is the list of all the games currently supported by MO2:

  •  Morrowind
  •  Oblivion(*)
  •  Fallout 3
  •  Fallout NV
  •  Tale of Two Wastelands (TTW)
  •  Skyrim
  •  Skyrim SE
  •  Skyrim VR 
  •  Fallout 4
  •  Fallout 4 VR
(*) Currently the steam version of OBSE is currently not supported and for the non steam version OBSE plugins need to be manually placed in the game Data folder to work. Help wanted to fix this.


Mod Organizer 2 supports third party plugins!
These work simply by being placed in the Plugins folder in the Mo2 install location. Mo2 offers plugin management though its settings menu.

You can write your own C++ and now even Python plugins (thanks to the work of AnyOldName3) to add functionalities to MO2, the Python ones being particularly interesting since they don't need you to compile any code as you can simply drop the .py file in the plugins folder.

Mo2 already uses plugins for many parts of the current functionalities (supported games are plugins, the BSA extractor is a plugin, the texture preview is a plugin etc...).
Your third party plugins can be distributed on Nexus or GitHub or wherever you prefer. If they work well and could be useful for a good amount of users, we would be happy to consider incorporating them in the main Mo2 release under your request.

Here you can find more info on writing your own Mo2 plugins:
Looking at existing plugins might be the best way to learn so we will list here the existing Mo2 plugins for reference.

List of the known MO2 Third Party Plugins :

List of all the Plugins that are integrated in the MO2 release:

Contact us though the discord server: if you want to know more about creating plugins or if you want your third party plugins to be listed on the Mo2 page.

Mod Organizer 2 should not be installed inside a system protected folder such as Programs Files (x86). 
Also avoid installing MO2 inside the Game folder as this causes problems with the vfs library.

Simplest for non-portable instanced installations, using the installer should be as simple as downloading and running the exe and specifying your install directory. It will download and install all necessary components required to run MO2.

If you want to update an existing Mo2 install using the installer, simply select your current MO2 folder as the install location and the installer will take care of the rest without endangering your modded setup.

As Windows tends to trust installer files better than manually extracted files, using the installer may provide a more problem-free experience.

Often ideal for portable installations, simply extract MO2 to a new location for each game you wish to manage. It can still be used for instanced installs.

Before unpacking the Mod Organizer 2 zip, make sure to open the properties and hit 'Unblock' if it shows up. If you don't do this then various libraries may fail to load or run when trying to use Mod Organizer. This can break certain installers or the virtualization system altogether.

If you wish to update an existing Mo2 installation it is generally a good idea to make a clean upgrade following these instructions:
1. Go to your MO2 installation directory, delete all directories and files EXCEPT for \downloads, \mods, \profiles, \overwrite, ModOrganizer.ini and categories.dat (leave those dirs and files, delete the rest).
2. Extract the new version to this location.
3. Start MO2.

Mod Organizer 2 depends on the MSVC 2017 runtime library. You must download and install this for MO2 to work properly (in addition to the Extra Steps). Download and install both the x86 and x64 versions of the 2017 redistributable: 
VC redist x64
VC redist x86
If you are not on Win10 you might also need:

Once installed, make sure the MO2 directory and/or files are excluded from any antivirus you may have installed. MO2's virtualization system hooks into the running applications and modifies system calls, and many antiviruses do not like this.

Migrating from Mod Organizer 1:
GamerPoets covered this in this video of his official MO2 guide (that we highly recommend):

Mod Organizer 2 works with the vast majority of tools. What this means is that they can be made to work on the "virtual" data tree.
Among the tested applications are: OBMM (though OMOD scripts may not compile properly), FOMM, MLOX, LOOT, Wrye Bash, FNIS, xEdit, DynDOLOD... and many more.

If you find an application that does not work, please report it to us.


Issues, problems and suggestions should be reported to the open discord server: ModOrganizerDevs or to the github page (in case they are not user specific): Github issues page.
Discord is also where dev builds are tested, bugs are reported and investigated, suggestions are discussed etc. There is a good number of users there willing to help people with issues in addition to the Developers, so that they don't have to handle everything personally.

Please don't post issues in the comment section, as monitoring them would be highly inefficient and inconvenient for the developers. Discord and GitHub offer much better and efficient ways to keep track of issues and debug directly with the users that have the problem.

Here are some of the themes and splash screens you can use to customize the look and feel of Mod Organizer 2:

If you would like your theme/stylesheet/splashscreen to be added to the list contact us on the MO2 Dev discord.