Building Ladybird on Linux and macOS: Full Instructions

Building Ladybird from source is the only way to run it during the current pre-alpha stage of development. The process follows a consistent pattern across all supported platforms: install system prerequisites, optionally configure a UI frontend, then run a single Python script that handles CMake configuration and compilation. This page covers every supported Unix-like system in detail, along with tips for choosing a UI, running debug builds, and attaching a debugger.

Prerequisites Overview

Before building, ensure the following are available on your system:

Requirement	Minimum version	Notes
CMake	3.30	Must be on `$PATH`; install from Kitware apt on Ubuntu
C++ compiler	clang-21 or gcc-14	CI uses these versions; see `find_compiler.py` for minimums
Ninja	Any recent	Build system driver
Qt6	6.x	Default UI on Linux; optional on macOS
nasm	Any recent	Assembler required by several library dependencies
Rust (via rustup)	Stable	rustup.rs

The CI pipeline uses clang-21 and gcc-14. If those exact versions are unavailable on your system, check Meta/Utils/find_compiler.py for the minimum compatible version your build system will accept.

Install System Dependencies

Base packages

sudo apt install autoconf autoconf-archive automake build-essential ccache cmake curl \
  fonts-liberation2 git glslang-tools libdrm-dev libgl1-mesa-dev libncurses-dev \
  libtool nasm ninja-build pkg-config python3-venv qt6-base-dev qt6-tools-dev-tools \
  qt6-wayland tar unzip zip

CMake 3.30 or newer (Ubuntu only)

The system CMake is often too old. Install from Kitware’s apt repository:

# Add Kitware GPG signing key
wget -O - https://apt.kitware.com/keys/kitware-archive-latest.asc 2>/dev/null \
  | gpg --dearmor - \
  | sudo tee /usr/share/keyrings/kitware-archive-keyring.gpg >/dev/null

# Authorize the Kitware apt source
echo "deb [signed-by=/usr/share/keyrings/kitware-archive-keyring.gpg] \
  https://apt.kitware.com/ubuntu/ $(lsb_release -sc) main" \
  | sudo tee /etc/apt/sources.list.d/kitware.list

# Update and install
sudo apt update -y && sudo apt install cmake -y

The Kitware apt repository is Ubuntu-only. Debian users should obtain CMake from the CMake download page.

C++23-capable compiler

Clang (recommended)
GCC (alternative)

Install from LLVM’s apt repository:

# Add LLVM GPG signing key
sudo wget -O /usr/share/keyrings/llvm-snapshot.gpg.key \
  https://apt.llvm.org/llvm-snapshot.gpg.key

# Authorize the LLVM apt source
echo "deb [signed-by=/usr/share/keyrings/llvm-snapshot.gpg.key] \
  https://apt.llvm.org/$(lsb_release -sc)/ \
  llvm-toolchain-$(lsb_release -sc)-21 main" \
  | sudo tee -a /etc/apt/sources.list.d/llvm.list

# Update and install clang and associated packages
sudo apt update -y && sudo apt install \
  clang-21 clangd-21 clang-tools-21 clang-format-21 clang-tidy-21 lld-21 -y

Install from the Ubuntu Toolchain PPA:

sudo add-apt-repository ppa:ubuntu-toolchain-r/test
sudo apt update && sudo apt install g++-14 libstdc++-14-dev

Audio support (optional)

sudo apt install libpulse-dev

sudo pacman -S --needed autoconf-archive base-devel ccache cmake curl git less \
  libgl nasm ninja python qt6-base qt6-tools ttf-liberation tar unzip zip

For PulseAudio audio playback support:

sudo pacman -S libpulse

sudo dnf install autoconf-archive automake ccache cmake curl git libdrm-devel \
  liberation-sans-fonts libglvnd-devel libtool nasm ncurses-devel ninja-build \
  patchelf perl-FindBin perl-IPC-Cmd perl-lib perl-Time-Piece qt6-qtbase-devel \
  qt6-qttools-devel qt6-qtwayland-devel tar unzip zip zlib-ng-compat-static

sudo zypper install autoconf-archive automake ccache cmake curl gcc14 gcc14-c++ \
  git liberation-fonts libglvnd-devel libtool nasm ncurses-devel ninja \
  qt6-base-devel qt6-tools-devel qt6-wayland-devel tar unzip zip

For audio playback:

sudo zypper install libpulse-devel

If packages are flagged as outdated during the build (e.g. autoconf 2.69 when 2.70 is needed), add the devel:tools:building repository. For Leap 15.6:

sudo zypper addrepo \
  https://download.opensuse.org/repositories/devel:tools:building/15.6/devel:tools:building.repo
sudo zypper refresh

openSUSE Leap ships Python 3.6 by default but the build requires Python 3.7+. Create a virtual environment using python312:

python3.12 -m venv ~/python312_venv
source ~/python312_venv/bin/activate

sudo xbps-install -Su   # optional: ensure packages are up to date
sudo xbps-install -S git bash gcc python3 curl cmake libtool zip unzip \
  linux-headers make pkg-config autoconf automake autoconf-archive nasm \
  ncurses-devel MesaLib-devel ninja qt6-base-devel qt6-tools-devel qt6-wayland-devel

Xcode 15 or Clang from Homebrew is required.

xcode-select --install
brew install autoconf autoconf-archive automake ccache cmake libtool nasm ninja pkg-config

To use Clang from Homebrew instead of Apple’s toolchain:

brew install llvm@21

To use the Qt UI on macOS (AppKit is the default):

brew install qt

Add your terminal application (Terminal.app or iTerm.app) to the Developer Tools section of Privacy & Security in System Settings. This reduces the slow startup time on first run of freshly compiled binaries caused by macOS binary validation.

pkg install autoconf-archive automake autoconf bash cmake ccache curl gmake gn \
  libdrm libtool libxcb libxkbcommon libX11 libXrender libXi nasm ninja patchelf \
  pkgconf python3 qt6-base tar unzip zip

zip, unzip, and tar are required by the vcpkg bootstrap step. If any are missing, the build will fail with a Python CalledProcessError traceback rather than a clear error message.

Build Ladybird

Clone the repository

git clone https://github.com/LadybirdBrowser/ladybird.git
cd ladybird

Run the build and launch

The ladybird.py script is the simplest and recommended way to build and run Ladybird. It handles CMake configuration, dependency management (via vcpkg), compilation, and launch in one command:

./Meta/ladybird.py run

This builds a Release build. Debug symbols are available in both Release and Debug builds.

(macOS with Homebrew Clang) Set compiler environment variables

If you installed llvm@21 from Homebrew and want to use it instead of Xcode’s toolchain:

CC=$(brew --prefix llvm)/bin/clang \
CXX=$(brew --prefix llvm)/bin/clang++ \
./Meta/ladybird.py run

Build Variants

Debug Build

To build with debug-optimized settings (uses -Og, includes full debug symbols):

BUILD_PRESET=Debug ./Meta/ladybird.py run

Run a Specific Executable

To run the JS REPL, the WebAssembly REPL, or another bundled tool instead of the browser:

./Meta/ladybird.py run js
./Meta/ladybird.py run wasm

Start in GDB

./Meta/ladybird.py gdb ladybird

Choosing a UI Frontend

Ladybird supports multiple UI frontends. The default is chosen automatically based on platform:

Frontend	Platform	Notes
AppKit	macOS	Default on macOS; native Objective-C UI
Qt	Linux, Windows (WSL2), others	Default on non-macOS
GTK 4	Linux	Experimental alternative
Android UI	Android	Native Android UI

To override the frontend, pass --gui to ladybird.py or set LADYBIRD_GUI_FRAMEWORK:

./Meta/ladybird.py run --gui=Qt

cmake --preset Release -DLADYBIRD_GUI_FRAMEWORK=Qt

Extra Packages for GTK 4

Building with LADYBIRD_GUI_FRAMEWORK=Gtk requires additional packages because some vcpkg dependencies (e.g. gettext) must be rebuilt from source:

Debian / Ubuntu
Arch / Manjaro
Fedora

sudo apt install bison libxkbcommon-dev

sudo pacman -S bison

sudo dnf install bison

Running Manually (Without ladybird.py)

The ladybird.py script ultimately invokes Ninja targets. You can run them directly from the build directory:

./Build/release/bin/Ladybird

open -W --stdout $(tty) --stderr $(tty) ./Build/release/bin/Ladybird.app

open -W --stdout $(tty) --stderr $(tty) ./Build/release/bin/Ladybird.app \
  --args https://ladybird.dev

ninja -C Build/release debug-ladybird

Debugging

CLion

Build with debug symbols

Build using the Debug preset (either BUILD_PRESET=Debug ./Meta/ladybird.py run or select the Debug Build Type in CLion’s CMake profile).

Launch Ladybird normally

Run ./Meta/ladybird.py run ladybird from a terminal.

Attach CLion to the process

In CLion, choose Run → Attach to Process. If debugging layout or rendering issues, filter for WebContent and attach to that process. Breakpoints, stepping, and variable inspection will now work.

Xcode / Instruments on macOS

Build the project

./Meta/ladybird.py build

Apply debug entitlements

Allow Instruments to attach by codesigning with the debug entitlements plist:

ninja -C Build/release apply-debug-entitlements
# or manually:
codesign -s - -v -f --entitlements Meta/debug.plist Build/release/bin/Ladybird.app

Open Instruments

Launch Instruments.app and point it at the Ladybird app bundle. All profiling and tracing tools are now available.

Building the project with Xcode directly is not supported. The Xcode project generated by CMake does not properly execute custom targets and does not handle all target names in the project. Use Instruments for profiling and CLion for interactive debugging.

Troubleshooting

CMake fails with "unable to find a build program corresponding to Ninja"

This error is a red herring produced by vcpkg, not Ninja itself. A dependency (often skia) failed to build. The real error appears earlier in the terminal output and in the log file identified in the CMake output, typically at Build/release/vcpkg-manifest-install.log.

error: building skia:x64-linux failed with: BUILD_FAILED
...
CMake Error: CMake was unable to find a build program corresponding to "Ninja".

Check the log file for the actual root cause, fix the underlying dependency issue (often a missing system library), then retry.

CMake version is outdated

Verify your version with cmake --version. You need 3.30 or newer. On Ubuntu, install from Kitware’s apt repository (see the Debian/Ubuntu tab above). On other systems, download a binary from the CMake website.

GCC is missing or too old

Check with gcc --version. If the binary is named differently (e.g. gcc-13), specify it explicitly when invoking CMake:

cmake ../.. -GNinja -DCMAKE_C_COMPILER=gcc-13 -DCMAKE_CXX_COMPILER=g++-13

"Legacy renegotiation is disabled" TLS error

Add the following to /etc/ssl/openssl.cnf:

[openssl_init]
ssl_conf = ssl_sect

[ssl_sect]
system_default = system_default_sect

[system_default_sect]
MinProtocol = TLSv1.2
CipherString = DEFAULT@SECLEVEL=1
Options = UnsafeLegacyRenegotiation

"Targets may link only to libraries" warning on macOS with Qt

This CMake warning is harmless. It appears when building with the Qt UI on macOS and does not prevent a successful build. You can safely ignore it.

Race condition / double-free on exit with llvmpipe

When running --headless=text or --headless=layout-tree on a system using the llvmpipe software rasterizer (common on virtual machines), Ladybird may occasionally crash on exit with double free or corruption (!prev). Run with --force-cpu-painting to work around this.

Build broken after git pull

If the build passes on CI, it should work locally. Try rebuilding the toolchain. If that does not help, try a clean repository. For persistent issues, ask in the #build-problems channel on the Ladybird Discord.

Get Started

Architecture

User Interfaces

Contributing

Core Libraries

Building Ladybird on Linux and macOS: Full Instructions

Prerequisites Overview

Install System Dependencies

Base packages

CMake 3.30 or newer (Ubuntu only)

C++23-capable compiler

Audio support (optional)

Build Ladybird

Build Variants

Debug Build

Run a Specific Executable

Start in GDB

Choosing a UI Frontend

Extra Packages for GTK 4

Running Manually (Without ladybird.py)

Debugging

CLion

Xcode / Instruments on macOS

Troubleshooting

​Prerequisites Overview

​Install System Dependencies

​Base packages

​CMake 3.30 or newer (Ubuntu only)

​C++23-capable compiler

​Audio support (optional)

​Build Ladybird

​Build Variants

​Debug Build

​Run a Specific Executable

​Start in GDB

​Choosing a UI Frontend

​Extra Packages for GTK 4

​Running Manually (Without ladybird.py)

​Debugging

​CLion

​Xcode / Instruments on macOS

​Troubleshooting

Prerequisites Overview

Install System Dependencies

Base packages

CMake 3.30 or newer (Ubuntu only)

C++23-capable compiler

Audio support (optional)

Build Ladybird

Build Variants

Debug Build

Run a Specific Executable

Start in GDB

Choosing a UI Frontend

Extra Packages for GTK 4

Running Manually (Without ladybird.py)

Debugging

CLion

Xcode / Instruments on macOS

Troubleshooting