Behaviour Graph Studio

Behaviour Graph Studio is a standalone desktop editor for Fallout 4 Havok behaviour files (.hkx). It runs outside the game and lets you inspect, edit, validate, compare, and preview behaviour graphs and animations.

Get started

Download a release from Nexus Mods, extract it anywhere on your computer, and run BehaviourGraphStudio or BehaviourGraphStudio.exe.

There is no installer and nothing needs to be added to your Fallout 4 folder.

For step-by-step help, see the public Behaviour Graph Studio guide.

What you can do

• Open Fallout 4 behaviour, character, project, skeleton, and animation .hkx files.
• Browse a file in a tree or graph view and inspect each object's editable fields.
• Open vanilla files directly from a Bethesda .ba2 archive without extracting the archive first.
• Edit supported values, names, symbols, bindings, states, transitions, generators, and arrays.
• Preview animation playback on a skeleton or skinned mesh.
• Check a graph or an entire project for broken references and missing animation files.
• Compare two behaviour files to find added, removed, and changed objects.
• Undo and redo changes before saving.

Supported edits are written through the native save pipeline. The original file is backed up as .bak; if an edit cannot be written safely, the application refuses to save and leaves the source file unchanged.

Quick start

1. Download and extract a release.
2. Start Behaviour Graph Studio.
3. Use Open to select an extracted .hkx file, or From archive... to browse a .ba2.
4. Select an object in the tree or graph to inspect it.
5. Make an edit, run Check graph, then save when the result is valid.

Files opened from a .ba2 are read-only copies. Copy one to a folder you control before editing it.

Known limitations and experimental features

BGS is conservative about unsupported formats and edits. Areas that are not fully reduced or validated are read-only, refused, or clearly marked in the application:

• Skeleton-mapper serialization/write-back and chain-mapper authoring are not complete. Shipped Fallout 4 files do contain chain and unmapped-bone data; automatic bone pairing is not proven.
• Reciprocal mapper generation is a construction tool based on the measured human fixture. It does not claim that every shipped mapper pair is symmetrical.
• Ragdoll and physics tools are primarily inspection and engineering previews. Drop/Recover is a constrained preview, not a full Havok solver; body-to-body collision simulation and full ragdoll authoring are not implemented.
• Some physics and cloth systems remain inspection-only. Havok 2018 support is incomplete; current Fallout 76 evidence covers Havok 2015.1.0, not a completed Havok 2018 implementation.
• Unsupported Havok layouts, classes, and conversion paths fail closed. BGS does not write guessed data; an unsupported operation leaves the source unchanged and reports why.

These boundaries are intentional for 1.1.0. See RELEASE-NOTES.md and the specialist notes under docs/ for the measured scope of the experimental tools.

Scan a load order from the command line

Behaviour Graph Studio can also scan a whole load order without opening the window — to vet a mod or gate a build in CI:

BehaviourGraphStudio.exe --scan-archives "D:\Mods\MyAnimationMod"
BehaviourGraphStudio.exe --scan-clips  "C:\MO2\Instances\Fallout 4"

--scan-archives finds corrupt behaviour files, --scan-modlist finds missing declared animations, and --scan-clips finds clips whose animation is absent from the merged load order. These are static findings rather than a reproduction of the game's runtime load path. Each mode returns an exit code (0/1/2) and takes --json for a machine-readable report. See the Headless scanning guide.

Requirements

• Windows 64-bit or Linux x64.
• A Fallout 4 installation is useful for opening game files, but it is not required to run the tool.
• No separate Havok tools, Java runtime, game SDK, or installation into the game directory is needed.

Build from source

Building requires the .NET 8 SDK.

dotnet run --project app/BehaviourStudio.csproj
dotnet test tools/tests/BehaviourGraph.Tests.csproj
dotnet publish app/BehaviourStudio.csproj -c Release -r linux-x64 -o out

For the pinned SDK, locked restores, the full three-part test surface, CI-parity commands, and both Windows/Linux publish flows, see CONTRIBUTING.md.

Help and feedback

• Read the public guide.
• Read CONTRIBUTING.md before changing or packaging BGS.
• Report reproducible problems through GitHub Issues.