Nightcap

Nightcap is Mocktail, tuned for playing on a real PC. It runs the Android x86_64 Roblox client on Linux, including a Linux userspace hosted by FreeBSD's Linuxulator. It provides the Android ABI and JNI pieces the client expects, then connects them to SDL3 and Vulkan or OpenGL on the Linux side.

Nightcap is an independent community project. It is not affiliated with Roblox Corporation or VinegarHQ and does not distribute the Roblox client.

About this fork

Nightcap is a fork of komaruworld/mocktail with extra fixes for playing on a PC. The program and config paths keep the mocktail name so upstream fixes still apply cleanly. The app ID is io.github.CoderDayton.nightcap, so Nightcap and upstream can be installed side by side.

• Lower input lag. Frames are shown as soon as they are ready instead of waiting in a queue.
• Sharper textures. Small textures are upscaled 4x by default, and you can replace any texture with your own PNG in ~/.config/mocktail/textures. A ready-made crosshair is in textures/. Set MOCKTAIL_SMALL_TEXTURE_UPSCALE=1 to turn the upscale off.
• ETC2 textures on any GPU. Games that use compressed mobile textures now render correctly on desktop GPUs, without stutter.
• No more error 319 kicks. Servers no longer drop you shortly after joining.
• Correct device info. Roblox sees your real RAM and screen size.
• Better desktop launcher. Runs on Wayland and always finds the installed binary.

Everything else works the same as upstream. See the roadmap for what is coming next, the changelog for what each release changed, performance for CPU load, heat and the knobs that change them, and the FAQ for Discord RPC, logs, and VR.

Install with Flatpak

flatpak install --user https://coderdayton.github.io/nightcap/nightcap.flatpakref
flatpak run io.github.CoderDayton.nightcap

Updates arrive through flatpak update. Nightcap is not on Flathub yet.

AppImage

Grab the AppImage from the latest release, make it executable, and run it:

chmod +x Nightcap-x86_64.AppImage
./Nightcap-x86_64.AppImage

Distribution packages

Each release also carries a DEB, an RPM, and a pacman package, with a .sha256 beside every file on the releases page:

sudo apt install ./nightcap_<version>_amd64.deb
sudo dnf install ./nightcap-<version>-1.x86_64.rpm
sudo pacman -U nightcap-<version>-1-x86_64.pkg.tar.zst

They install /usr/bin/mocktail, so they conflict with upstream's mocktail package. Nightcap is not in any distribution repository or the AUR; the recipes under packaging/aur are kept for local builds only.

Or build and install from source using the steps under Building.

How it works

Roblox APK -> signature and ABI checks -> Bionic + JNI -> SDL3 + Vulkan/OpenGL

The APK is checked before any native code is loaded. It is downloaded on first launch and is not bundled with Nightcap. The last working copy is kept in case an update fails.

A leftover .previous_good-recovery.json in the payload store marks pending recovery after a publication or restoration failure and blocks further payload publication and garbage collection. Check current.json and previous_good.json against the saved recovery state and fix the underlying problem before manually removing the marker.

Screenshots

FFlag overrides

Put a JSON object in $XDG_CONFIG_HOME/mocktail/fflags.json (usually ~/.config/mocktail/fflags.json). Nightcap applies it on the next launch.

PC profiles use the legacy Charts page by default to avoid the blank screen caused by Color3 errors in the newer SDUI page. An explicit FFlagLuaAppChartsAppPage override takes precedence over this default.

{
  "FFlagExample": "True",
  "DFIntExample": "120"
}

Settings

Edit ~/.config/mocktail/config.yaml. Useful options:

• graphics.frame_rate_limit: display to unlock FPS to your monitor's rate.
• graphics.vsync: off for the lowest lag, at the cost of tearing.
• graphics.backend: opengl if Vulkan does not work on your GPU.

Building

Linux x86_64 is supported. Experimental FreeBSD 15.1 Linuxulator support has been tested with an x86_64 Fedora 44 userspace. On FreeBSD, Nightcap runs inside Linuxulator; it is not a native FreeBSD binary. Building requires CMake 3.20+, Git, pkg-config, LLD, binutils, a C++17 compiler, SDL 3.4+, SDL3_ttf, Vulkan, EGL, libplacebo, fontconfig, libcurl, OpenSSL, libelf, libyaml, libpng, minizip, Capstone 5, utf8proc, nlohmann/json, GTK4, libadwaita 1.6+, and WebKitGTK 6.0.

See the FreeBSD Guide for setup and launch instructions.

Ubuntu 26.04+

sudo apt update
sudo apt install build-essential cmake git ninja-build pkg-config lld \
  libsdl3-dev libsdl3-ttf-dev libcurl4-openssl-dev libssl-dev \
  nlohmann-json3-dev libyaml-dev libpng-dev libelf-dev libminizip-dev \
  libcapstone-dev libgtk-4-dev libadwaita-1-dev libwebkitgtk-6.0-dev \
  libutf8proc-dev libfontconfig1-dev libegl-dev libvulkan-dev \
  libplacebo-dev zlib1g-dev

Arch Linux

sudo pacman -S --needed base-devel cmake git ninja pkgconf lld sdl3 sdl3_ttf \
  curl openssl nlohmann-json libyaml libpng libelf minizip capstone gtk4 \
  libadwaita webkitgtk-6.0 libutf8proc fontconfig libglvnd \
  libplacebo vulkan-headers vulkan-icd-loader zlib

Fedora 44+

sudo dnf install gcc-c++ cmake git ninja-build pkgconf-pkg-config lld \
  SDL3-devel SDL3_ttf-devel libcurl-devel openssl-devel \
  nlohmann-json-devel libyaml-devel libpng-devel elfutils-libelf-devel \
  minizip-ng-compat-devel \
  capstone-devel gtk4-devel libadwaita-devel webkitgtk6.0-devel \
  utf8proc-devel fontconfig-devel libglvnd-devel vulkan-headers \
  vulkan-loader-devel libplacebo-devel zlib-ng-compat-devel

git clone --recurse-submodules https://github.com/CoderDayton/nightcap.git
cd nightcap
make build
./build/mocktail

To install it for your user, with an app menu entry and Roblox link handling:

make install PREFIX=~/.local

Use sudo make install instead to install system-wide under /usr. To make Roblox website links open the build tree copy without installing, run make register-url-handler.

To build and install the Flatpak from source, install flatpak-builder and run make flatpak. It builds with 2 parallel jobs to keep memory use low. Pass FLATPAK_JOBS=N to make flatpak, or set MOCKTAIL_FLATPAK_JOBS=N for scripts/build_flatpak.sh, to change that.

To run the same checks as CI before each commit and push, install lefthook and run once:

lefthook install

Known limitations

Nightcap does not currently work with hardened_malloc. Using hardened_malloc may cause Nightcap to fail to start or crash during runtime. Run Nightcap without hardened_malloc enabled.

License

Apache License 2.0. Third-party components keep their own licenses.

Support

Support this fork by giving it a star or with cryptocurrency:

• LTC: LdABR2ELRYrUESWZWrEk1uNx38gHHMuHUU
• SOL: tjeDnPoWeyW8zfTf8c5CVAm5QTV8vFPaPouaScAdwfT

Support the upstream project, which does most of the heavy lifting:

• USDT (TON): UQCi6Yzcc9cOctoij6n_r1K90-OdVxAT0D_xo2UzGKkQaJDY
• USDT (TRC20): TNPMG9Vig2xiuo2r1QqnXRChPH7Vu28Jmx