🧠 Brains complement: IF an unreal-engine-skills-manager tool (external MCP) exists in this session, call it with {action: "load", skill: "blueprint-fundamentals"} for UE domain knowledge on this topic — correct APIs, architecture, best practices — and treat it as the rubric for any review / "best practices" question. If no such tool is available (e.g. running under Claude Code or Codex without that MCP), skip this line entirely and proceed with this skill alone — do NOT attempt the call.

Blueprint System Skill

For node-level graph editing (adding nodes, connecting pins, wiring logic, timers, layout), load the blueprint-graphs skill.

Critical Rules

⚠️ Engine BlueprintTools args are {refPath} objects, NOT strings

Every UObject/UClass argument to the engine BlueprintTools toolset (blueprint, asset_type, graph, parent_class, …) is a reference object {"refPath": "<object path>"}, and these tools return the same shape. Passing a plain string fails with "<x> is not a valid object path for property '<arg>'". This rule is only for the engine BlueprintTools call_tool path — VibeUE's own unreal.BlueprintService.* Python methods still take plain string paths.

The refPath must be the full object path — /Game/Dir/Asset.Asset (the asset name repeated after the dot). A bare package path (/Game/Dir/Asset, no .Asset) is rejected. Two safe ways to get one:

# (a) Reuse what create/load returns — it is already a {refPath} object:
bp_ref = call_tool("create", "editor_toolset.toolsets.blueprint.BlueprintTools",
                   {"folder_path": "/Game/BP", "asset_name": "BP_X",
                    "asset_type": {"refPath": "/Script/Engine.Actor"}})["returnValue"]

# (b) Build one from a package path you already have:
def bp_ref_of(p):  # "/Game/Dir/BP_X" -> {"refPath": "/Game/Dir/BP_X.BP_X"}
    name = p.rsplit("/", 1)[-1].split(".")[0]
    return {"refPath": p if "." in p.rsplit("/", 1)[-1] else f"{p}.{name}"}

All the arguments={"blueprint": path, ...} / {"blueprint": bp, ...} examples in the sub-docs are shorthand — wrap the path with bp_ref_of(...) (or reuse the returned ref) when you actually call. On success these tools return {"returnValue": null}; an error comes back as a Parameter error.

⚠️ Creating a Blueprint — engine BlueprintTools.create

Blueprint basics now live on the engine's BlueprintTools toolset (VibeUE extends the native MCP endpoint). Create a Blueprint with call_tool, not unreal.BlueprintService.create_blueprint (that method was cut):

# CORRECT — folder_path + asset_name are strings; asset_type is a {refPath} class reference.
result = call_tool(
    tool_name="create",
    toolset_name="editor_toolset.toolsets.blueprint.BlueprintTools",
    arguments={"folder_path": "/Game/Blueprints", "asset_name": "BP_MyActor",
               "asset_type": {"refPath": "/Script/Engine.Actor"}},
)
# -> {"returnValue": {"refPath": "/Game/Blueprints/BP_MyActor.BP_MyActor"}}
bp_ref = result["returnValue"]   # reuse this {refPath} object for later BlueprintTools calls

The folder and asset name are passed separately (folder_path + asset_name) — do not jam a full asset path into one argument. asset_type is the parent class as a {refPath}: /Script/Engine.Actor, /Script/Engine.Pawn, /Script/Engine.Character, or a Blueprint's generated class "/Game/.../BP_Base.BP_Base_C".

Blueprint Types in add_variable — engine BlueprintTools.add_variable

Adding a variable is also an engine BlueprintTools call now (unreal.BlueprintService.add_variable was cut). Use call_tool with blueprint, name, type_name (and add_object_variable / add_struct_variable for object- and struct-typed variables):

# CORRECT — blueprint is a {refPath} object; name/type_name are strings
call_tool(
    tool_name="add_variable",
    toolset_name="editor_toolset.toolsets.blueprint.BlueprintTools",
    arguments={"blueprint": {"refPath": "/Game/BP_MyActor.BP_MyActor"}, "name": "Health", "type_name": "float"},
)

When the variable's type is a Blueprint class, use the Blueprint asset name directly in type_name. Do not add _C, and do not construct a generated class path — just use the name ("BP_Enemy", or the full "/Game/Blueprints/BP_Enemy"). Appending _C ("BP_Enemy_C") or guessing a generated class path is wrong; the type system resolves Blueprint names automatically via asset search.

Engine structs need the F prefix: color variables are "FLinearColor" / "FColor" — plain "LinearColor" / "Color" is not resolved. Unsure of a type string? Use the surviving unreal.BlueprintService.search_variable_types("Linear") to look it up.

Supported primitive type_name values (exact): bool, int, float, byte, name, string, text, Vector, Rotator, Transform, Vector2D, LinearColor. Use int (not int32) and float (not double) — add_variable rejects int32/double with "Unknown type 'int32'. Supported: …". For other engine structs (e.g. FColor, FGameplayTag) use add_struct_variable with struct_type; for object/class refs use add_object_variable with object_class as a {refPath}:

# Object-reference variable — object_class is a {refPath} to the class
call_tool("add_object_variable", "editor_toolset.toolsets.blueprint.BlueprintTools",
    {"blueprint": {"refPath": "/Game/BP_MyActor.BP_MyActor"}, "name": "DeathFX",
     "object_class": {"refPath": "/Script/Niagara.NiagaraSystem"}})

⚠️ Adding a function graph — engine BlueprintTools.add_function_graph

Creating a function graph moved to the engine toolset (create_function / add_function on BlueprintService were cut). Use call_tool with blueprint + graph_name:

call_tool(
    tool_name="add_function_graph",
    toolset_name="editor_toolset.toolsets.blueprint.BlueprintTools",
    arguments={"blueprint": {"refPath": "/Game/Blueprints/BP_MyActor.BP_MyActor"}, "graph_name": "DoThing"},
)

Refining the graph afterward still uses the surviving VibeUE delta methods (add_function_parameter, add_function_local_variable, get_function_parameters, get_function_info, override_function, open_function_graph).

⚠️ Method Name Gotchas

WRONG	CORRECT
get_component_info(path, name)	get_component_info(type) - takes ONLY type!

⚠️ Property Name Gotchas

WRONG	CORRECT
info.inputs	info.input_parameters
var.name	var.variable_name

⚠️ Python Naming: Boolean b Prefix Is Stripped

UE Python strips the lowercase b prefix from boolean properties. Always use the name without it:

C++ name	Python name
bAlreadyOverridden	already_overridden
bIsEventStyle	is_event_style
bIsNativeEvent	is_native_event
bEnabled	enabled

Do not use b_already_overridden, b_is_event_style, etc. — these will raise AttributeError.

Exception: the string-based CDO accessors get_property / set_property take the native C++ property name, so booleans KEEP the b prefix there ("bReplicates", not "replicates"). See the next section.

⚠️ CDO Properties: get_property / set_property (replication, lifespan, etc.)

Use these to read/write Class Default Object properties like replication or initial lifespan:

import unreal
bp = "/Game/Blueprints/TestActor"

# READ — returns a single value: str, or None if the property wasn't found. NOT a (success, value) tuple!
value = unreal.BlueprintService.get_property(bp, "bReplicates")   # "True" / "False" (a STRING)
life  = unreal.BlueprintService.get_property(bp, "InitialLifeSpan")  # "5.000000"

# WRONG — raises ValueError: too many values to unpack
# success, value = unreal.BlueprintService.get_property(bp, "bReplicates")

# WRITE — values are strings; returns bool
unreal.BlueprintService.set_property(bp, "bReplicates", "True")

# Compile via the engine BlueprintTools toolset (compile_blueprint was cut from BlueprintService):
# call_tool(tool_name="compile_blueprint",
#           toolset_name="editor_toolset.toolsets.blueprint.BlueprintTools",
#           arguments={"blueprint": {"refPath": "/Game/Blueprints/TestActor.TestActor"}})
unreal.EditorAssetLibrary.save_asset(bp)

Rules:

• Returns str or None — UE Python collapses bool Func(..., Out&) into one return value. This applies to every get_*_info method too (get_variable_info, get_function_info, get_component_info, get_node_details): they return the info struct or None, never a tuple.
• Property names are the native C++ names: bReplicates, InitialLifeSpan, bCanBeDamaged — the b prefix is NOT stripped here (a stripped name returns None).
• Values read back as strings: compare value == "True", not value is True.

⚠️ Info Struct Fields (don't guess — these are the complete lists)

get_blueprint_info(path) → BlueprintDetailedInfo: blueprint_name, blueprint_path, parent_class, is_widget_blueprint, variables, functions, components.

Struct	Fields
BlueprintFunctionInfo (from list_functions)	function_name, return_type, parameters, is_override, is_pure — there is no function_type and no input_parameters (that's the Detailed struct)
BlueprintFunctionDetailedInfo (from get_function_info)	function_name, graph_guid, input_parameters, output_parameters, local_variables, is_override, is_pure, node_count — there is no return_type; return values are entries in output_parameters (each param: parameter_name, parameter_type, is_output, is_reference, default_value)
BlueprintVariableInfo	variable_name, variable_type, category, is_public, is_exposed, default_value
BlueprintVariableDetailedInfo (from get_variable_info)	variable_name, variable_type, type_path, category, default_value, tooltip, is_array, is_set, is_map, is_instance_editable, is_blueprint_read_only, is_expose_on_spawn, is_expose_to_cinematics, is_private, replication_condition — booleans use the is_ prefix (instance_editable alone raises AttributeError)
BlueprintLocalVariableInfo (in BlueprintFunctionDetailedInfo.local_variables)	variable_name, friendly_name, variable_type, display_type, default_value, category, guid, is_const, is_reference, is_array, is_set, is_map — local variables are NOT parameters: there is no parameter_name
BlueprintPinInfo (from get_node_pins / node.pins)	pin_name, pin_type, is_input, is_connected, default_value — direction is the single is_input bool; there is no is_output (use not pin.is_input)
BlueprintNodeTypeInfo (from discover_nodes)	display_name, category, spawner_key, node_class, tooltip, is_pure, is_latent, keywords — the description text is tooltip, not description
BlueprintComponentInfo	component_name, component_class, attach_parent, is_root_component, is_scene_component, is_inherited, children
BlueprintGraphInfo (from list_graphs)	graph_name, graph_kind, node_count
BlueprintNodeInfo (from get_nodes_in_graph)	node_id, node_type, node_title, pos_x, pos_y, pin_names, pins
BlueprintCompileResult	success, num_errors, num_warnings, errors, warnings
ComponentDetailedInfo (from get_component_info)	name, display_name, class_path, category, parent_class, is_scene_component, is_primitive_component, property_count, function_count — there is no description
ComponentTypeInfo (from get_available_components)	name, display_name, class_path, category, base_class, is_scene_component, is_primitive_component, is_abstract
ComponentPropertyInfo (from get_all_component_properties)	property_name, property_type, category, value, is_editable, is_inherited

Component API quick reference (all on unreal.BlueprintService)

These signatures are complete — no need to discover_python_class them again:

Method	Notes
get_available_components(search_filter="", max_results=50) → [ComponentTypeInfo]	Discover addable component types by partial name match
get_component_info(component_type) → ComponentDetailedInfo or None	Takes ONLY the type name — no blueprint path
list_components(bp) / get_component_hierarchy(bp) → [BlueprintComponentInfo]	Both return the same flat list — use attach_parent / children / is_root_component fields to render the tree
component_exists(bp, name) → bool	Fast idempotency check before adding
add_component(bp, type, name, parent_name="") → bool	Compiles inline. See root behavior below
remove_component(bp, name, remove_children=True) → bool	Removes children too by default
reparent_component(bp, name, new_parent) → bool
set_root_component(bp, name) → bool	New root must be a SceneComponent. Old auto-generated DefaultSceneRoot is removed; an old user-created root and any other root-level scene components become children of the new root
get_component_property(bp, comp, prop) → str or None
set_component_property(bp, comp, prop, value) → bool	value is a STRING — see formats below
get_all_component_properties(bp, comp, include_inherited=True) → [ComponentPropertyInfo]	list_component_properties is an alias
compare_components(bp_a, comp_a, bp_b, comp_b) → str or None	Diff as text; same or different blueprints
set_collision_settings(bp, comp, collision_enabled, object_type, collision_profile, channel_responses) → bool	Collision lives in BodyInstance — set_component_property cannot reach it

Root component behavior: components added with no parent_name go to root level. The first scene component added this way replaces the auto-generated DefaultSceneRoot and becomes the root; later parentless scene components become floating siblings, NOT children of the root. To build a hierarchy, pass parent_name when adding, or use reparent_component / set_root_component.

⚠️ Property Value String Formats (set_component_property)

Values are strings in UE export-text syntax. Check property_type via get_all_component_properties before guessing a struct format:

Property type	Format example
float / int32 / bool	"5000.0", "25", "true"
FVector / FRotator	"(X=0,Y=0,Z=50)", "(Pitch=0,Yaw=90,Roll=0)"
FColor (e.g. light LightColor)	"(R=255,G=127,B=0,A=255)" — integer bytes 0–255
FLinearColor	"(R=1.0,G=0.5,B=0.0,A=1.0)" — floats 0–1
Enum (e.g. IntensityUnits)	"Candelas"

❌ Common mistake: LightColor is FColor, so passing LinearColor-style floats like "(R=1,G=0.5,B=0)" silently produces a nearly-black light (R=1 of 255), not orange.

⚠️ StateTree Dispatcher Variable Type

To add a StateTree delegate dispatcher variable to a Blueprint task (e.g. STT_*):

# Use type "FStateTreeDelegateDispatcher" — NOT "EventDispatcher".
# add_variable is the engine BlueprintTools toolset call (BlueprintService.add_variable was cut):
call_tool(
    tool_name="add_variable",
    toolset_name="editor_toolset.toolsets.blueprint.BlueprintTools",
    arguments={"blueprint": bp_path, "name": "FinishRotatingDispatcher", "type_name": "FStateTreeDelegateDispatcher"},
)

"EventDispatcher" is a Blueprint-only concept and is not a valid type string. The correct type for StateTree delegate transitions is the USTRUCT FStateTreeDelegateDispatcher. After adding this variable, use bind_transition_to_delegate on the StateTree to link it to a transition.

Event Dispatchers (regular Blueprint multicast delegates)

Use the dedicated dispatcher API — NOT add_variable — to create the multicast delegates that appear in the Blueprint editor's Event Dispatchers section:

Method	What it does
add_event_dispatcher(bp_path, name)	Adds the dispatcher (member variable + signature graph). Skeleton is recompiled inline; the dispatcher is callable immediately.
add_event_dispatcher_parameter(bp_path, name, param_name, param_type, is_array=False, container_type="")	Adds a parameter to the dispatcher's signature. Subscribers receive these as inputs.
add_call_delegate_node(bp_path, graph, name, pos_x, pos_y)	Spawns the "Call <Name>" broadcast node on a UK2Node_CallDelegate. Wire the broadcast into its execute pin.
remove_event_dispatcher(bp_path, name)	Removes the dispatcher and its signature graph.

import unreal

bp = "/Game/StateTree/BP_Cube"

# 1. Create the dispatcher (no compile needed before placing nodes — skeleton is regenerated inline)
unreal.BlueprintService.add_event_dispatcher(bp, "FinishedLooking")

# 2. (Optional) Add parameters to the signature
unreal.BlueprintService.add_event_dispatcher_parameter(bp, "FinishedLooking", "Direction", "FRotator")

# 3. Spawn the Call node and wire something into its execute pin
call_id = unreal.BlueprintService.add_call_delegate_node(bp, "EventGraph", "FinishedLooking", 1400, -700)
unreal.BlueprintService.connect_nodes(bp, "EventGraph", timeline_id, "Finished", call_id, "execute")

# 4. Compile (engine BlueprintTools toolset) + save
# call_tool(tool_name="compile_blueprint",
#           toolset_name="editor_toolset.toolsets.blueprint.BlueprintTools",
#           arguments={"blueprint": bp})
unreal.EditorAssetLibrary.save_asset(bp)

Pins on the Call node: execute (input exec), then (output exec), self (input target — defaulted to Self), plus one input pin per signature parameter.

Subscribing to it elsewhere:

• Preferred — add_delegate_bind_on_variable(other_bp, graph, variable_name, "FinishedLooking", x, y) when the dispatcher lives on the class of an existing variable (e.g. Cube : BP_Cube_C). Mirrors add_function_call_on_variable: derives the owner class from the variable's type, creates the bind node + Get, and auto-wires Target. Pair with add_custom_event_node and wire CustomEvent.OutputDelegate → Bind.Delegate.
• Lower-level — add_delegate_bind_node(other_bp, graph, "<owner class>", "FinishedLooking", x, y) when you have no variable to derive from. <owner class> accepts "Self", native class names (with/without U/A prefix), Blueprint asset paths (/Game/.../BP_Cube), or short BP names with/without _C (BP_Cube, BP_Cube_C). You wire the Target pin yourself.

Common mistakes:

• ❌ add_variable(bp, "FinishedLooking", "EventDispatcher") — "EventDispatcher" is not a real type string; use add_event_dispatcher instead.
• ❌ Treating the dispatcher like a regular variable (add_get_variable_node on it produces a delegate-getter, not a broadcast). The broadcast node is UK2Node_CallDelegate and is created only by add_call_delegate_node.
• ❌ Skipping the compile before saving the asset. The skeleton compiles inline on dispatcher creation, but the final asset still needs the engine BlueprintTools.compile_blueprint toolset call before save_asset to ensure the generated class is up-to-date.

Blueprint Interfaces (implement / remove)

Add or remove a Blueprint Interface on a Blueprint class — the equivalent of Class Settings → Interfaces → Add in the editor.

Method	What it does
add_interface(bp_path, interface)	Implements the interface on the Blueprint. No-op (returns True) if it is already implemented. Marks the Blueprint structurally modified and recompiles it inline.
remove_interface(bp_path, interface)	Removes the interface from the Blueprint. Marks structurally modified and recompiles inline.

import unreal

bp = "/Game/Blueprints/BP_Player"

# Prefer the FULL interface asset path — most reliable resolution
unreal.BlueprintService.add_interface(bp, "/Game/Interfaces/BPI_Interactable")

# Short name also works IF the interface asset is already loaded in the editor
unreal.BlueprintService.add_interface(bp, "BPI_Interactable")

# Persist (both methods compile inline, but still save the asset)
unreal.EditorAssetLibrary.save_asset(bp)

# Remove it later
unreal.BlueprintService.remove_interface(bp, "BPI_Interactable")
unreal.EditorAssetLibrary.save_asset(bp)

Notes & gotchas:

• Prefer the full asset path (e.g. /Game/Interfaces/BPI_Interactable). Short-name resolution only finds interface Blueprints that are already loaded in the editor; a full path always loads and resolves.
• Both methods recompile the Blueprint inline (CompileBlueprint) but do not save it — call EditorAssetLibrary.save_asset(bp) afterward to persist.
• add_interface is idempotent — calling it for an interface that is already implemented returns True without duplicating it.
• After adding an interface, its functions appear as overridable events/functions; use override_function(bp_path, function_name) to implement them in the graph.
• Both return bool (True on success). A False from add_interface means either the interface path could not be resolved, or it resolved to an asset that is not a Blueprint Interface (e.g. a normal Blueprint or one merely parented to UInterface) — check the log and pass a real Blueprint Interface asset path.
• The interface must be a true Blueprint Interface (BPTYPE_Interface), created with BlueprintInterfaceFactory. add_interface validates this and returns False for non-interface classes rather than letting the compile fail.

---

Task Index

Task	Workflow	Sample script (run via execute_python_code)
Create a Blueprint + variables	workflows.md → Create a Blueprint	scripts/create_blueprint.txt
Add components + set properties	workflows.md → Add components	scripts/add_component.txt
Add an event dispatcher (delegate)	workflows.md → Event dispatcher	scripts/event_dispatcher.txt
Implement a Blueprint interface	workflows.md → Implement an interface	scripts/add_interface.txt
Inspect a Blueprint (components, parent class)	introspection.md	—
Node-level graph editing	load the blueprint-graphs skill	—

Sub-docs

• workflows.md — step-by-step create/component/dispatcher/interface workflows with copy-paste Python.
• introspection.md — what Blueprint introspection works/doesn't in UE 5.7 (CDO reads, parent class via asset tags, listing BPs by class, getting level actors).

Verification

After any edit: compile via the engine BlueprintTools.compile_blueprint toolset call (call_tool(tool_name="compile_blueprint", toolset_name="editor_toolset.toolsets.blueprint.BlueprintTools", arguments={"blueprint": path})) and check the result's success / num_errors, then unreal.EditorAssetLibrary.save_asset(path). Don't claim success until compile reports zero errors.