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An open source implementation of the Ultima Online Classic Client.

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ClassicUO is an open source implementation of the Ultima Online Classic Client. This client is intended to emulate all standard client versions and is primarily tested against Ultima Online free shards.

The client is currently under heavy development but is functional. The code is based on the FNA-XNA framework. C# is chosen because there is a large community of developers working on Ultima Online server emulators in C#, because FNA-XNA exists and seems reasonably suitable for creating this type of game.

ClassicUO is natively cross platform and supports:

  • Windows [DirectX 11, OpenGL, Vulkan]
  • Linux [OpenGL, Vulkan]
  • macOS [Metal, OpenGL, MoltenVK]

Download & Play!

Platform Link
Windows x64 Download
Linux x64 Download
macOS Download

Or visit the ClassicUO Website

How to build the project

Clone repository with:

git clone --recursive


The binary produced will work on all supported platforms.

You'll need Visual Studio 2019. The free community edition should be fine. Once that is installed:

  • Open ClassicUO.sln from the root of the repository.

  • Select "Debug" or "Release" at the top.

  • Hit F5 to build. The output will be in the "bin/Release" or "bin/Debug" directory.


  • Open a terminal and enter the following commands.



sudo apt update
sudo apt install dirmngr gnupg apt-transport-https ca-certificates software-properties-common lsb-release
sudo apt-key adv --keyserver hkp:// --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
sudo apt-add-repository "deb stable-`lsb_release -sc` main"

Check signature

gpg: key A6A19B38D3D831EF: public key "Xamarin Public Jenkins (auto-signing) <>" imported
gpg: Total number processed: 1
gpg:               imported: 1
sudo apt install mono-complete



Fedora 29

rpm --import ""
su -c 'curl | tee /etc/yum.repos.d/mono-centos8-stable.repo'
dnf update

Fedora 28

rpm --import ""
su -c 'curl | tee /etc/yum.repos.d/mono-centos7-stable.repo'
dnf update
sudo dnf install mono-devel



sudo pacman -S mono mono-tools


mono --version
Mono JIT compiler version (tarball Tue Dec 10 10:36:32 UTC 2019)
Copyright (C) 2002-2014 Novell, Inc, Xamarin Inc and Contributors.
    TLS:           __thread
    SIGSEGV:       altstack
    Notifications: epoll
    Architecture:  amd64
    Disabled:      none
    Misc:          softdebug
    Interpreter:   yes
    LLVM:          yes(610)
    Suspend:       hybrid
    GC:            sgen (concurrent by default)
  • Navigate to ClassicUO scripts folder: cd /your/path/to/ClassicUO/scripts

  • Execute script. If you want build a debug version of ClassicUO just pass "debug" as argument like: ./ debug. Probably you have to set the file executable with with the command chmod -x

  • Navigate to /your/path/to/ClassicUO/bin/[Debug or Release]


All the commands should be executed in terminal. All global package installs should be done only if not yet installed.

After the first run, ignore the error message and a new file called settings.json will be automatically created in the directory that contains ClassicUO.exe.

Other useful commands:

  • msbuild /t:Clean /p:Configuration=Debug
  • msbuild /t:Clean /p:Configuration=Release


Everyone is welcome to contribute! The GitHub issues and project tracker are kept up to date with tasks that need work.


The code itself has been written using the following projects as a reference:


This work is released under the BSD 4 license. This project does not distribute any copyrighted game assets. In order to run this client you'll need to legally obtain a copy of the Ultima Online Classic Client. Using a custom client to connect to official UO servers is strictly forbidden. We do not assume any responsibility of the usage of this client.

Ultima Online(R) © 2020 Electronic Arts Inc. All Rights Reserved.