Unreal Engine 4/5 Scripting System

Lua scripting system platform, C++ Modding API, SDK generator, blueprint mod loader, live property editor and other dumping utilities for UE4/5 games.

Major features

• Lua Scripting API: Write lua mods based on the UE object system
• Blueprint Modloading: Spawn blueprint mods automatically without editing/replacing game files
• C++ Modding API: Write C++ mods based on the UE object system
• Live Property Viewer and Editor: Search, view, edit & watch the properties of every loaded object, great for debugging mods or figuring out how values are changed during runtime
• UHT Dumper: Generate Unreal Header Tool compatible C++ headers for creating a mirror .uproject for your game
• C++ Header Dumper: Generate standard C++ headers from reflected classes and blueprints, with offsets
• Universal UE Mods: Unlock the game console and other universal mods
• Dumpers for File Parsing: Generate .usmap mapping files for unversioned properties
• UMAP Recreation Dumper: Dump all loaded actors to file to generate .umaps in-editor
• Other Features, including Experimental features at times

Targeting UE Versions: From 4.7 To 5.8

The goal of UE4SS is not to be a plug-n-play solution that always works with every game. The goal is to have an underlying system that works for most games. You may need to update AOBs on your own, and there's a guide for that below.

Basic Installation

The easiest installation is via downloading the non-dev version of the latest non-experimental build from Releases and extracting the zip content to {game directory}/GameName/Binaries/Win64/.

If your game is in the custom config list, extract the contents from the relevant folder to Win64 as well.

If you are planning on doing mod development using UE4SS, you can do the same as above but download the zDEV version instead.

Command Line Options

If RE-UE4SS is installed via proxy DLL, the following command line options are available:

• --disable-ue4ss - Temporarily disable UE4SS without uninstalling by launching the game with this argument.
• --ue4ss-path <path> - Specify a custom path to UE4SS.dll. Supports both absolute paths (e.g., C:\custom\UE4SS.dll) and relative paths (e.g., dev\builds\UE4SS.dll relative to the game executable directory). Useful for testing different UE4SS builds without modifying installation files.

Environment Variables

RE-UE4SS supports the following environment variables:

• UE4SS_MODS_PATHS - Semicolon-separated list of additional mods directories to load. Paths are processed in reverse order (first entry has highest priority), similar to the PATH variable. Example: C:\SharedMods;D:\GameMods;E:\TestMods.

Links

Full installation guide

Fixing compatibility problems

Lua API - Overview

Generating UHT compatible headers

Custom Game Configs

Creating Compatible Blueprint Mods

UE4SS Discord Server Invite

Unreal Engine Modding Discord Server Invite

Build requirements

• Windows is required for native builds. Native Linux builds are not currently supported, but Windows binaries can be cross-compiled from Linux using the separate prerequisites and instructions below.
• For native Windows builds, a version of MSVC that supports C++23:
• MSVC toolset version >= 14.43.0
• MSVC version >= 19.43
• Visual Studio version >= 17.13
• More compilers will hopefully be supported in the future.
• Rust toolchain >= 1.73.0
• CMake >= 3.22
• A build system: either Ninja or MSVC (included with Visual Studio)

Build instructions

1. Clone the repo.
2. Execute this command: git submodule update --init --recursive Make sure your Github account is linked to your Epic Games account for UE source access. Do not use the --remote option because that will force third-party dependencies to update to the latest commit, and that can break things. You will need your github account to be linked to an Epic games account to pull the Unreal pseudo code submodule.

There are several different ways you can build UE4SS.

Building from CLI

Build Modes

The build modes are structured as follows: <Target>__<Config>__<Platform>

Currently supported options for these are:

• Target
• Game - for regular games on UE versions greater than UE 4.21
• LessEqual421 - for regular games on UE versions less than or equal to UE 4.21

• CasePreserving - for games built with case preserving enabled

• Config

• Dev - development build
• Debug - debug build
• Shipping - shipping(release) build

• Test - build for tests

• Platform

• Win64 - 64-bit windows

Basic Build Commands

To build UE4SS with CMake, use the following commands:

# Configure with Ninja (recommended for faster builds, single-configuration)
cmake -B build_cmake_Game__Shipping__Win64 -G Ninja -DCMAKE_BUILD_TYPE=Game__Shipping__Win64

# Build with Ninja
cmake --build build_cmake_Game__Shipping__Win64

# Or configure with MSVC (multi-configuration, allows switching configs without reconfiguring)
cmake -B build_cmake_Game__Shipping__Win64 -G "Visual Studio 17 2022"

# Build with MSVC (requires --config flag)
cmake --build build_cmake_Game__Shipping__Win64 --config Game__Shipping__Win64

Configuration Options

CMake allows you to configure various build options. Here are some useful options:

Proxy Path

By default, UE4SS generates a proxy based on C:\Windows\System32\dwmapi.dll. To change this, set the CMake variable:

cmake -B build -DUE4SS_PROXY_PATH="<path to proxy dll>" -DCMAKE_BUILD_TYPE=Game__Shipping__Win64

Profiler Flavor

By default, UE4SS has profiling disabled (None). To enable profiling, you need both a profiler flavor AND a build configuration that includes STATS:

# STATS are enabled by default in Dev and Test builds
cmake -B build -DPROFILER_FLAVOR=<Tracy|Superluminal|None> -DCMAKE_BUILD_TYPE=Game__Dev__Win64

[!NOTE] Profiling requires STATS support. By default, Dev and Test configurations include STATS, while Shipping and Debug do not. You can manually enable STATS for any configuration by adding compile definitions: bash cmake -B build -DPROFILER_FLAVOR=Tracy -DCMAKE_BUILD_TYPE=Game__Shipping__Win64 -DCMAKE_CXX_FLAGS="-DSTATS"

Helpful CMake Commands

Command	Description
cmake -B <build_dir> -G <generator>	Configure the project with a specific generator (Ninja or "Visual Studio 17 2022")
cmake --build <build_dir>	Build with Ninja (single-config generator)
cmake --build <build_dir> --config <mode>	Build with MSVC (multi-config generator, --config required)
cmake --build <build_dir> --clean-first	Clean and rebuild (add --config <mode> for MSVC)
cmake --build <build_dir> --target <target>	Build a specific target (add --config <mode> for MSVC)
cmake --build <build_dir> --verbose	Build with verbose output (add --config <mode> for MSVC)

Opening in an IDE

Visual Studio

CMake has built-in support for generating Visual Studio solutions:

cmake -B build -G "Visual Studio 17 2022"

Then open the generated .sln file in the build directory.

Alternatively, Visual Studio 2022 has native CMake support - you can open the folder directly in Visual Studio and it will automatically detect the CMakeLists.txt file.

CLion / Other CMake IDEs

Most modern IDEs (CLion, Visual Studio Code with CMake Tools, etc.) have native CMake support. Simply open the project folder and the IDE will automatically detect and configure the CMake project.

Note that you should also commit & push the submodules that you've updated if the reason why you updated was not because someone else pushed an update, and you're just catching up to it.

Cross-Compiling Windows Binaries on Linux

UE4SS supports cross-compilation from Linux to Windows using two approaches: xwin (recommended) or msvc-wine.

Prerequisites for All Cross-Compilation

• Rust toolchain >= 1.73.0 with the x86_64-pc-windows-msvc target: bash rustup target add x86_64-pc-windows-msvc For Rust installations without rustup, install the Windows target standard library separately. It must match the installed Rust compiler build.
• CMake >= 3.22
• Ninja build system

Option 1: Cross-Compiling with xwin (Recommended)

xwin downloads and packages the Microsoft CRT headers/libraries and Windows SDK headers/libraries needed for cross-compilation, without requiring a Windows installation.

Prerequisites

• LLVM/Clang with Windows target support, including clang-cl, lld-link, and the MASM-compatible llvm-ml assembler: ```bash # On Ubuntu/Debian sudo apt install clang lld llvm

# On Arch Linux sudo pacman -S clang lld llvm

# On Enterprise Linux 10 (e.g. RHEL, CentOS Stream, AlmaLinux) sudo dnf install clang lld llvm - [xwin](https://github.com/Jake-Shadle/xwin), installed using Cargo:bash cargo install xwin `` - Wine and Linuxbinfmt_miscsupport for a complete cross-build. UE4SS runs Windows build-time tools such asproxy_generator.exedirectly. The host must be able to execute Windows PE binaries without an explicitwine` command. A headless Wine installation is sufficient to build UE4SS.

Setup

1. If you have not already done so, clone the repository and initialise its submodules as described in Build instructions. Change into the root of the cloned repository (normally RE-UE4SS/, containing CMakeLists.txt). Run the commands below from that directory.

2. Download and unpack the Microsoft SDK and CRT into the repository's xwin/ directory (installing the xwin executable alone does not install the SDK): bash xwin --accept-license splat --output ./xwin Both xwin CMake toolchains and build.sh find the SDK and CRT there automatically, but if you prefer to store the SDK and CRT elsewhere, set XWIN_DIR to that directory before configuring or building, for example export XWIN_DIR="$HOME/.xwin". When set, XWIN_DIR overrides the repository-local default.

3.3. Wine must be registered with Linux's binfmt_misc mechanism to allow Windows .exe files to be executed directly during the build. Your distribution may already have configured this.

Check with:

bash cat /proc/sys/fs/binfmt_misc/status grep -il '^interpreter .*wine' /proc/sys/fs/binfmt_misc/* 2>/dev/null

You should see a short list including output similar to:

text enabled /proc/sys/fs/binfmt_misc/DOSWin

The handler name may differ between distributions. If binfmt_misc is not enabled, or no Wine interpreter is listed, follow the configuration instructions below.

On most Linux distributions, you can make the Wine registration persistent across reboots using the following procedure. These instructions use systemd, which is included in most mainstream Linux distributions. If your distribution uses a different init system, consult its documentation for making binfmt_misc registrations persistent.

bash sudo mkdir -p /etc/binfmt.d printf '%s\n' ':DOSWin:M::MZ::/usr/bin/wine:' | sudo tee /etc/binfmt.d/wine.conf sudo systemctl restart systemd-binfmt.service Use the actual absolute path to Wine if it is not /usr/bin/wine. Distribution packaging and registration may differ. Check the configuration by executing a Windows console .exe directly, without prefixing the command with wine.

Optional: Suppress Wine Diagnostic Output

Wine can produce extensive diagnostic output when running Windows build-time tools, particularly on headless systems. To suppress it for the current shell session:

export WINEDEBUG=-all

You can also prefix an individual command (for example, WINEDEBUG=-all cmake --build build_xwin), or add the export to your shell startup configuration if you prefer. This setting is optional; unset it when you need Wine diagnostics. The xwin modes of build.sh suppress Wine diagnostics automatically.

Building Manually with CMake

Run the following commands from the repository root. Select one toolchain and use its own build directory; CMake caches the compiler selection. Both xwin toolchains need llvm-ml with -m64 for the Windows x64 proxy assembly.

# Configure with xwin-clang-cl (MSVC-compatible compiler interface)
cmake -S . -B build_xwin -G Ninja \
  -DCMAKE_BUILD_TYPE=Game__Shipping__Win64 \
  -DCMAKE_TOOLCHAIN_FILE=cmake/toolchains/xwin-clang-cl-toolchain.cmake \
  -DCMAKE_ASM_MASM_COMPILER:FILEPATH="$(command -v llvm-ml)" \
  -DCMAKE_ASM_MASM_FLAGS:STRING=-m64

# Build
cmake --build build_xwin

Alternatively, use the xwin-clang toolchain (GNU-style compiler interface) in a separate build directory:

cmake -S . -B build_xwin_clang -G Ninja \
  -DCMAKE_BUILD_TYPE=Game__Shipping__Win64 \
  -DCMAKE_TOOLCHAIN_FILE=cmake/toolchains/xwin-clang-toolchain.cmake \
  -DCMAKE_ASM_MASM_COMPILER:FILEPATH="$(command -v llvm-ml)" \
  -DCMAKE_ASM_MASM_FLAGS:STRING=-m64

cmake --build build_xwin_clang

Building with build.sh Script

The xwin toolchains use llvm-ml -m64 automatically when building through build.sh. Invoke the script with bash; executable file permissions are not required. By default it builds only the UE4SS target; use --target all for the complete build, including the proxy DLL.

# Build the complete project with xwin-clang-cl
bash tools/buildscripts/build.sh --toolchain xwin-clang-cl --target all

# Or build the complete project with xwin-clang
bash tools/buildscripts/build.sh --toolchain xwin-clang --target all

# Build a specific configuration (UE4SS target by default)
bash tools/buildscripts/build.sh --toolchain xwin-clang-cl --build-config Game__Debug__Win64

# Clean, full build with verbose output
bash tools/buildscripts/build.sh --toolchain xwin-clang-cl --target all --clean --verbose

Option 2: Cross-Compiling with msvc-wine

msvc-wine uses actual MSVC tools running under Wine. This provides maximum compatibility but requires more setup.

Prerequisites

• Wine: ```bash # On Ubuntu/Debian sudo apt install wine wine64 winbind

# On Arch Linux sudo pacman -S wine samba ``` - msvc-wine - Follow their installation guide to install MSVC tools - Clang (for wine-clang-cl mode) or use MSVC's cl.exe (for wine-msvc mode)

Setup

1. Install msvc-wine following the official instructions. By default, this installs to ~/my_msvc/opt/msvc.

2. Make sure the msvc-wine tools are in your PATH: bash export PATH="$HOME/my_msvc/opt/msvc/bin/x64:$PATH"

3. Set the Wine prefix (optional): bash export WINE_PREFIX=~/.wine

Building Manually with CMake

# Configure with wine-clang-cl toolchain (clang-cl under wine)
cmake -B build_wine \
  -G Ninja \
  -DCMAKE_BUILD_TYPE=Game__Shipping__Win64 \
  -DCMAKE_TOOLCHAIN_FILE=cmake/toolchains/wine-clang-cl-toolchain.cmake

# Or use wine-msvc toolchain (MSVC cl.exe under wine)
cmake -B build_wine \
  -G Ninja \
  -DCMAKE_BUILD_TYPE=Game__Shipping__Win64 \
  -DCMAKE_TOOLCHAIN_FILE=cmake/toolchains/wine-msvc-toolchain.cmake

# Build
cmake --build build_wine

Building with build.sh Script

# Build with wine-clang-cl
bash tools/buildscripts/build.sh --toolchain wine-clang-cl

# Or build with wine-msvc
bash tools/buildscripts/build.sh --toolchain wine-msvc

# Build specific configuration
bash tools/buildscripts/build.sh --toolchain wine-clang-cl --build-config Game__Debug__Win64

Build Output

Cross-compiled binaries will be in the chosen build directory under <BuildMode>/bin/. For example, the manual xwin-clang-cl build produces:

build_xwin/
└── Game__Shipping__Win64/
    └── bin/
        ├── UE4SS.dll
        ├── dwmapi.dll  (proxy DLL)
        └── ... (other files)

The build.sh --toolchain xwin-clang-cl example instead uses build_xwin-clang-cl_Game__Shipping__Win64/.

Debugging Under Wine

When using wine-based toolchains, you can debug crashes and issues using Wine's debugger.

Using winedbg

# Debug a running program
winedbg ./path/to/game.exe

# Debug a crash dump
winedbg crash_2024_12_26_07_39_15.dmp

Important Notes for Debugging

• Debug symbols (.pdb files) are not stored in minidump files
• You must have the exact same .pdb file that corresponds to the .dll that crashed
• The easiest way to ensure matching symbols: 1. Note the git commit hash when you built UE4SS 2. When debugging a crash, checkout that exact commit 3. Rebuild to generate matching .pdb files 4. Then debug the minidump

Tips

• If you encounter "access denied" errors, ensure you have winbind or samba installed
• PDB files are generated in the same directory as the DLL files

Updating git submodules

If you want to update git submodules, you do so one of three ways: 1. You can execute git submodule update --init --recursive to update all submodules. 2. You can also choose to update submodules one by one, by executing git submodule update --init --recursive deps/<first-or-third>/<Repo>. Do not use the --remote option unless you actually want to update to the latest commit. 3. If you would rather pick a specific commit or branch to update a submodule to then cd into the submodule directory for that dependency and execute git checkout <branch name or commit>. The main dependency you might want to update from time to time is deps/first/Unreal.

Credits

All contributors since the project became open source: https://github.com/UE4SS-RE/RE-UE4SS/graphs/contributors

• Original Creator The original creator no longer wishes to be involved in or connected to this project. Please respect their wishes, and avoid using their past usernames in connection with this project.
• Archengius
• UHT compatible header generator
• CasualGamer
• Injector code & aob scanner is heavily based on his work, 90% of that code is his.
• SunBeam
• Extra signature for function 'GetFullName' for UE4.25.
• Regex to check for proper signature format when loaded from ini.
• Lots and lots of work on signatures
• tomsa
• const char* to vector\ converter
  • tomsa: Idea & most of the code
  • Original Creator: Nibblet support
• boop / usize
• New UFunction hook method
• RussellJ
• Blueprint Modloader inspiration
• Narknon
• Certain features and maintenance/rehosting of the project
• DeadMor0z
• Certain features and Lua updates/maintenance
• OutTheShade
• Unreal Mappings (USMAP) Generator
• DmgVol
• Inspiration for map dumper
• Buckminsterfullerene
• Rewriting the documentation, various fixes
• trumank
• Lua bindings generator, various fixes, automation & improvements
• localcc
• C++ API

Thanks to everyone who helped with testing

• GreenHouse
• Otis_Inf
• SunBeam
• Motoson
• hooter
• Synopis
• Buckminsterfullerene

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