Speedrun and TAS tool for Half-Life & friends.
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Bunnymod XT

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Bunnymod XT (BXT for short) is a cross-platform tool that provides speedrunning and TAS-related features for GoldSource games such as Half-Life and its modifications.

Used by hundreds if not thousands of speedrunners worldwide.

Bunnymod XT provides state-of-the-art speedrunning and TASing features and utilities, ranging from detailed HUDs to advanced autostrafing. It is a successor to the obsoleted hlspbunny and Bunnymod Pro.


Despite the "mod" in Bunnymod XT, this is not a mod in the usual sense. Most Half-Life modifications work by modifying the Half-Life SDK and distributing the resulting DLLs. This includes the deprecated Bunnymod Pro. The downside is that while you can "mod" Half-Life itself, you cannot "mod" another Half-Life mod. This is a serious limitation for speedrunners intending to speedrun Half-Life mods and expansions.

To rectify this, Bunnymod XT injects into the Half-Life process while leaving every file on the disk intact. This means all modifications are done on-the-fly in RAM. This also means Bunnymod XT supports a wider range of Half-Life engines, from WON to the latest Steam.



The instructions are described here.


  1. Download or build libBunnymodXT.so.
  2. Download this helper script.
  3. Run chmod +x runhl.sh to make the script executable.
  4. Edit the helper script by appending the absolute path of libBunnymodXT.so to the end of the export LD_PRELOAD= line. For instance, export LD_PRELOAD=/home/me/dir/libBunnymodXT.so.
  5. Launch Half-Life from the terminal by executing ./runhl.sh.


On the Wiki pages.

Environment variables

  • BXT_SCRIPT - if set to a filename of a hltas script, loads the non-shared RNG from that script on load.
  • BXT_LOGFILE - if set, logs all Bunnymod XT messages into a file with that filename.
  • SPTLIB_DEBUG - if set to 1, logs all dlopen, dlclose and dlsym calls.



Building on Windows requires

Run the following commands, replacing path\to\boost\base\dir and \path\to\rapidjson\base\dir with paths to Boost and RapidJSON base directories respectively:

git clone https://github.com/YaLTeR/BunnymodXT
cd BunnymodXT
git submodule update --init --recursive
mkdir build
cd build
cmake -DBOOST_ROOT=path\to\boost\base\dir -DRapidJSON_ROOT=path\to\rapidjson\base\dir -Wno-dev ..

Then compile the ALL_BUILD project from the generated VS solution.

If you want to make a Windows XP-compatible build, additionally specify -T v141_xp (or the equivalent for your Visual Studio version) in the cmake command line arguments.


Building on Linux requires

Many of these dependencies can be installed from a package manager.

To build, run the following commands, replacing path/to/rapidjson/base/dir with path to the RapidJSON base directory:

git clone https://github.com/YaLTeR/BunnymodXT
cd BunnymodXT
git submodule update --init --recursive
mkdir build
cd build
cmake -DRapidJSON_ROOT=path/to/rapidjson/base/dir -Wno-dev ..

Note that -DBOOST_ROOT is not required as CMake should be able to find the location of Boost in your system. In case it couldn't, you need to specify it manually like the case on Windows.