version: "1.0.1" name: ue-mcp-blueprint description: Use when authoring or modifying Unreal Blueprint assets through ue-mcp. Covers the read-then-write discipline, node/pin wiring, component (SCS) hierarchy, variables, interfaces, compilation, and the difference between pin defaults and linked inputs. Pulls in any time the user asks to create, edit, or inspect a Blueprint.

ue-mcp blueprint authoring

The blueprint tool covers reading, authoring, and compiling Blueprints. The default workflow is read → mutate → compile, never fire-and-forget.

Authoring a graph body: prefer the Epic DSL (#711)

When you are authoring the contents of a graph (event graph, function body, macro) - a set of nodes plus their wiring - do not default to node-by-node add_node/connect_pins. Reach for Epic's graph DSL first:

1. blueprint(action="epic_get_graph_dsl_docs") - read the S-expression grammar once.
2. blueprint(action="epic_write_graph_dsl", ...) - author + compile the whole graph body in one call.

The DSL authors and compiles an entire graph in a single round-trip, which is materially faster and more reliable than stitching individual K2Nodes together (one correct pass vs several failed iterations). Use it for graph bodies whenever it is available.

Availability / fallback. The epic_* actions come from Epic's ToolsetRegistry and require UE 5.8+ with the Epic toolset plugins enabled. Check with epic(action="status"). When they are unavailable (pre-5.8, or the registry is off), fall back to the native node path below.

Keep using the native actions for read/discovery, SCS components, CDO/class defaults, interfaces + event dispatchers, structured compile/validate, and anything with no Epic equivalent - the native path adds idempotency and rollback the raw tools lack. See the ue-mcp-epic-routing skill for the full epic-vs-native decision.

Discovery before authoring

For any existing Blueprint:

• blueprint(action="read", assetPath=...) - structure (parent, components, graphs)
• blueprint(action="read_graph_summary", assetPath=..., graphName=...) - lightweight node+edge summary (~10KB) - use this before read_graph (which can be 100KB+)
• blueprint(action="list_graphs", assetPath=...) - every graph in the BP including event graphs, functions, macros, interface impls
• blueprint(action="list_variables" | "list_functions" | "list_local_variables") - the member surface. list_functions covers the same graphs as list_graphs (own functions, parent overrides, interface impls, event graphs and their entry points, macros, collapsed subgraphs), each tagged with kind and source; pass includeInherited: true to also see overridable functions not implemented yet
• blueprint(action="get_execution_flow", assetPath=..., entryPoint=...) - trace exec pins from an entry point
• blueprint(action="get_dependencies", assetPath=..., reverse=false|true) - classes/functions/assets this BP uses, or callers if reverse: true

Mutation recipe

1. Create the skeleton - blueprint(action="create", assetPath, parentClass?).
2. Add variables + components - add_variable, add_component (pass parentComponent for SCS hierarchy).
3. Build graphs - add_node each K2Node, set_node_property for pin defaults, connect_pins to wire exec + data.
4. Compile - blueprint(action="compile", assetPath). Compilation errors come back in the result; fix them before proceeding.

Node wiring fundamentals

• add_node takes nodeClass as a K2Node class short name (K2Node_CallFunction, K2Node_VariableGet, K2Node_DynamicCast, K2Node_IfThenElse, etc.) plus nodeParams for class-specific fields (FunctionReference, VariableReference, TargetType).
• Pin defaults vs linked values: set_node_property writes a literal default onto a pin; connect_pins wires a pin to another node's output. A literal default is ignored once a pin is linked.
• read_node_property reads either a pin default or a reflected node UPROPERTY - use this to verify the pin was actually set before compiling.
• Graphs with duplicate names (rare but possible after rename) can be disambiguated by passing graphIndex alongside graphName.

Components (SCS)

• add_component creates a node in the Simple Construction Script. Pass parentComponent to put the new component under an existing parent - otherwise it becomes a top-level child of the scene root.
• set_component_property writes on the child BP's InheritableComponentHandler override template, not on the parent - the parent stays untouched. This matters when editing inherited components.
• read_component_properties dumps every UPROPERTY on the template, including array contents.
• reparent_component moves an SCS node to a new parent.

CDO (class defaults)

• set_class_default writes a UPROPERTY on the Blueprint CDO (the class default object). For actor tick settings specifically, use set_actor_tick_settings - it handles bCanEverTick, bStartWithTickEnabled, TickInterval in one call.

Interfaces + event dispatchers

• create_interface + add_interface - the implement-side.
• add_event_dispatcher - fires a multicast delegate from the BP.

Verify before compile

• blueprint(action="validate") runs the compiler diagnostics without saving. Cheaper round-trip when iterating.
• blueprint(action="read_graph_summary") after mutations confirms the graph shape.