LimboAI - Behavior Trees & State Machines

LimboAI is an open-source C++ plugin for Godot Engine 4 that combines Behavior Trees and Hierarchical State Machines to create complex AI behaviors. It includes a visual behavior tree editor, built-in documentation, a visual debugger, and an extensive demo project with tutorial. Fully supports GDScript for creating custom tasks and states.

Behavior Trees

• Create, edit and save BehaviorTree resources with a dedicated visual editor.

• Execute trees using the BTPlayer node.

• Build complex behaviors by combining composites, decorators, conditions, and actions.

• Create custom tasks in GDScript by extending BTAction, BTCondition, BTDecorator, and BTComposite.

• Blackboard system for sharing data between tasks — with plans, scopes, parameters, and inspector integration.

• Reuse trees across resources with BTSubtree.

• Visual Debugger to inspect BT execution in running scenes.

• In-game visualization via BehaviorTreeView and performance monitors.

Hierarchical State Machines

• Implement state logic by extending LimboState.

• LimboHSM manages states and transitions, and can be nested.

• Event-based transitions for clean decoupling of state logic.

• Combine with behavior trees via BTState for advanced reactive AI.

• Delegation option for rapid prototyping and game jams.

Highlights

• GDExtension support — no custom engine builds needed.

• Unit tested — BT tasks and HSM covered by tests.

• Demo + Tutorial — extensive demo project with step-by-step examples.

• Built-in docs — class documentation accessible from the editor.

Links

• Documentation

• Getting Started

• GitHub Repository

• Discord Community

Author: limbonaut — License: MIT — Logo & demo art: CC BY 4.0