behavior-trees

Create the blackboard first with BlackboardService.create_blackboard, add keys, then call BehaviorTreeService.create_behavior_tree with the board path. Add nodes with add_node using class names like BTComposite_Selector, and every mutator saves the asset automatically.

Use set_node_blackboard_key with the decorator's node path, property name, and key name. Never use set_node_property_value for key selectors, because the service validates the key type against the selector's filter and the engine would silently clear a bad binding on save.

In UE 5.8 many numeric BT properties are FValueOrBBKey structs, so pass '(DefaultValue=3.5,Key="")' instead of a plain number. Read the current value with get_node_property_value first and mirror its shape.

No. Writes are refused while PIE runs, while an editor is open on the asset, or when the commit would damage the runtime tree. Refusal messages name the mechanism and the fix, so close the editor or stop PIE first.

Run find_blackboard_key_references first to list every BT selector bound to that key. Renaming returns the list of bindings that broke, so you can rebind them afterward; SelfActor on a parent-less board cannot be removed.

build_tree replays JSON through ordinary mutators with one save per node, so it suits tens of nodes, not bulk imports. Composite decorators cannot be recreated because they are editor-only sub-graphs, and injected subtree nodes are read-only.