Unreal Widget Editing

Widget Editing

Edit UMG Widget Blueprint UI layouts via a text-based tree representation. The widget tree (visual hierarchy) uses the [WidgetTree] section. For editing the event graph and functions of a Widget Blueprint, use the unreal-blueprint-editing skill — Widget Blueprints are Blueprints, so EventGraph/Function/Variables sections work identically.

Prerequisite: UE editor running with UCP plugin enabled.

API

CDO: /Script/UnrealClientProtocolEditor.Default__NodeCodeEditingLibrary

Section Types for Widget Blueprints

A Widget Blueprint's Outline returns both widget tree and graph sections:

WidgetTree Text Format

The widget tree uses indentation-based text format where depth represents parent-child relationships:

[WidgetTree]
CanvasPanel_0: {"Type":"CanvasPanel"}
  Image_BG: {"Type":"Image", "Slot":{"Anchors":"(Minimum=(X=0,Y=0),Maximum=(X=1,Y=1))", "Offsets":"(Left=0,Top=0,Right=0,Bottom=0)"}}
  VerticalBox_Main: {"Type":"VerticalBox", "Slot":{"Anchors":"(Minimum=(X=0.5,Y=0.5),Maximum=(X=0.5,Y=0.5))"}}
    TextBlock_Title: {"Type":"TextBlock", "Text":"Hello World", "Slot":{"HorizontalAlignment":"HAlign_Center"}}
    Button_Submit: {"Type":"Button", "Slot":{"Padding":"(Left=0,Top=10,Right=0,Bottom=0)"}, "bIsVariable":true}
      TextBlock_BtnLabel: {"Type":"TextBlock", "Text":"Submit"}

Format Rules

• Indentation = hierarchy: 2 spaces per level. Root widget has no indentation.
• Widget name is the key: TextBlock_Title, Button_Submit, etc. These are the widget's GetName().
• Type: Widget class name (e.g., CanvasPanel, TextBlock, Button, Image). Resolved via reflection.
• Slot: Layout properties from the parent panel's slot type, as a nested JSON object.
• bIsVariable: If true, the widget is accessible from the Blueprint graph (e.g., for binding events or setting properties at runtime). Only serialized when true.
• Other properties: Non-default widget properties, serialized via UE reflection.

Slot Properties by Panel Type

Different panel types use different slot types with different layout properties:

CanvasPanelSlot (parent is CanvasPanel):

• LayoutData.Anchors: (Minimum=(X=0,Y=0),Maximum=(X=1,Y=1)) — anchor presets
• LayoutData.Offsets: (Left=0,Top=0,Right=0,Bottom=0) — position/size offsets
• LayoutData.Alignment: (X=0.5,Y=0.5) — pivot alignment
• bAutoSize: true/false
• ZOrder: integer

VerticalBoxSlot / HorizontalBoxSlot (parent is VerticalBox/HorizontalBox):

• Padding: (Left=0,Top=10,Right=0,Bottom=0)
• Size: (SizeRule=Fill,Value=1.0) or (SizeRule=Auto,Value=1.0)
• HorizontalAlignment: HAlign_Fill, HAlign_Left, HAlign_Center, HAlign_Right
• VerticalAlignment: VAlign_Fill, VAlign_Top, VAlign_Center, VAlign_Bottom

OverlaySlot (parent is Overlay):

• Padding: (Left=0,Top=0,Right=0,Bottom=0)
• HorizontalAlignment: same as above
• VerticalAlignment: same as above

GridSlot (parent is GridPanel):

• Row, Column: integer
• RowSpan, ColumnSpan: integer

Common Widget Types

Workflow

1. Outline — see available sections (WidgetTree + graph sections)
2. ReadGraph("WidgetTree") — get the UI hierarchy
3. Understand the tree — indentation shows parent-child relationships
4. Modify — add/remove/rearrange widgets, change properties
5. WriteGraph("WidgetTree", text) — apply changes

For logic changes (event bindings, property updates at runtime):

1. ReadGraph("EventGraph") — use the unreal-blueprint-editing skill
2. Reference widgets by name (widgets with bIsVariable:true are accessible in graphs)

Key Rules

1. Indentation matters: 2 spaces per level. Incorrect indentation will create wrong parent-child relationships.
2. Widget names must be unique within the tree.
3. Root widget (depth 0) must be a panel widget (CanvasPanel, VerticalBox, etc.).
4. Only panel widgets can have children. Don't indent a child under a non-panel widget like TextBlock.
5. Set bIsVariable:true on any widget you need to reference from the Blueprint graph.
6. ReadGraph before WriteGraph — always read first to understand the current structure.
7. Slot properties depend on the parent panel type. A widget under VerticalBox uses VerticalBoxSlot properties, not CanvasPanelSlot.
8. All operations support Undo (Ctrl+Z).

Error Handling

• Unknown widget class: "Unknown widget class: ...".
• Failed to create widget: "Failed to create widget: ...".
• Check diff object in response for nodes_added, nodes_removed.