UE Editor Tools

You are an expert in extending the Unreal Editor with custom tools and workflows.

Context

Read .agents/ue-project-context.md for editor module structure, engine version, team workflows, and project-specific conventions before providing guidance.

Before You Start

Ask which area the user needs if not clear:

• Editor Utility Widget — UMG panel run from editor right-click
• Blutility — UAssetActionUtility or UActorActionUtility scripted actions
• Detail Customization — Custom property panel (IDetailCustomization / IPropertyTypeCustomization)
• Custom Editor Mode — Viewport mode with specialized interaction (FEdMode)
• Asset Type Actions — Content Browser integration for a custom asset type
• Editor Subsystem — Editor-lifetime singleton (UEditorSubsystem)
• Menu / Toolbar Extension — UToolMenus additions to main menu, toolbars, context menus

---

Editor Module Setup

All editor-extending code must live in a module with "Type": "Editor". Never put UnrealEd / PropertyEditor includes in a Runtime module without #if WITH_EDITOR guards.

{ "Name": "MyGameEditor", "Type": "Editor", "LoadingPhase": "PostEngineInit" }

// MyGameEditor.Build.cs — key dependencies
PrivateDependencyModuleNames.AddRange(new string[] {
    "Core", "CoreUObject", "Engine", "UnrealEd",
    "Slate", "SlateCore", "EditorStyle",
    "PropertyEditor",   // IDetailCustomization, IPropertyTypeCustomization
    "EditorSubsystem",  // UEditorSubsystem
    "Blutility",        // UEditorUtilityWidget, UAssetActionUtility
    "ToolMenus",        // UToolMenus
    "AssetTools",       // FAssetTypeActions_Base
    "MyGame"
});

Module skeleton — every registration in StartupModule must be mirrored in ShutdownModule:

IMPLEMENT_MODULE(FMyGameEditorModule, MyGameEditor)

void FMyGameEditorModule::StartupModule()
{
    FPropertyEditorModule& PropMod =
        FModuleManager::LoadModuleChecked<FPropertyEditorModule>("PropertyEditor");
    PropMod.RegisterCustomClassLayout(
        UMyDataAsset::StaticClass()->GetFName(),
        FOnGetDetailCustomizationInstance::CreateStatic(
            &FMyDataAssetCustomization::MakeInstance));
    PropMod.NotifyCustomizationModuleChanged();

    UToolMenus::RegisterStartupCallback(
        FSimpleMulticastDelegate::FDelegate::CreateRaw(
            this, &FMyGameEditorModule::RegisterMenus));
}

void FMyGameEditorModule::ShutdownModule()
{
    if (FModuleManager::Get().IsModuleLoaded("PropertyEditor"))
    {
        FModuleManager::GetModuleChecked<FPropertyEditorModule>("PropertyEditor")
            .UnregisterCustomClassLayout(UMyDataAsset::StaticClass()->GetFName());
    }
    UToolMenus::UnRegisterStartupCallback(this);
    if (UToolMenus* TM = UToolMenus::TryGet()) { TM->UnregisterOwner(this); }
}

Full boilerplate with asset type actions, editor modes, and factory: references/editor-module-setup.md

---

Editor Utility Widgets

UEditorUtilityWidget (from EditorUtilityWidget.h) extends UUserWidget for editor-only UMG panels. Create as a Blueprint subclass (right-click Content Browser > Editor Utilities > Editor Utility Widget). Run: right-click the widget asset > Run Editor Utility Widget. Or subclass in C++:

#pragma once
#include "EditorUtilityWidget.h"
#include "MyEditorUtilityWidget.generated.h"

UCLASS()
class MYGAMEEDITOR_API UMyEditorUtilityWidget : public UEditorUtilityWidget
{
    GENERATED_BODY()
public:
    UFUNCTION(BlueprintCallable, Category = "My Tools")
    void BatchRenameSelectedAssets(const FString& Prefix);
};

// .cpp
void UMyEditorUtilityWidget::BatchRenameSelectedAssets(const FString& Prefix)
{
    for (UObject* Asset : UEditorUtilityLibrary::GetSelectedAssets())
    {
        if (Asset)
        {
            const FString Src = Asset->GetOutermost()->GetName(); // e.g. /Game/Folder/OldName
            UEditorAssetLibrary::RenameAsset(Src, FPaths::GetPath(Src) / Prefix + TEXT("_") + Asset->GetName());
        }
    }
}

Key UEditorUtilityLibrary functions (from EditorUtilityLibrary.h):

Function	Purpose
GetSelectedAssets()	Currently selected Content Browser assets
GetSelectedAssetsOfClass(UClass*)	Filter selection by class
UEditorAssetLibrary::DeleteAsset(Path)	Delete asset; RenameAsset for move/rename
GetSelectionSet()	Selected level actors
SyncBrowserToFolders(TArray<FString>)	Sync content browser view

Content browser filters: Use FARFilter with IAssetRegistry::GetAssets for programmatic asset queries by class, path, or tags.

Open a widget programmatically:

GEditor->GetEditorSubsystem<UEditorUtilitySubsystem>()
    ->SpawnAndRegisterTab(LoadObject<UEditorUtilityWidgetBlueprint>(
        nullptr, TEXT("/Game/EditorWidgets/BP_MyTool")));

---

Blutility: Scripted Actions

UAssetActionUtility — Asset Right-Click Actions

Any UFUNCTION(CallInEditor) on a UAssetActionUtility subclass appears in the Content Browser context menu. Set SupportedClasses in Class Defaults to filter by asset type.

#pragma once
#include "AssetActionUtility.h"   // Engine/Source/Editor/Blutility/Classes/AssetActionUtility.h
#include "MyAssetActionUtility.generated.h"

UCLASS()
class MYGAMEEDITOR_API UMyAssetActionUtility : public UAssetActionUtility
{
    GENERATED_BODY()
public:
    UFUNCTION(CallInEditor, Category = "My Tools")
    void SetTextureCompressionToUI()
    {
        for (UObject* Asset : UEditorUtilityLibrary::GetSelectedAssets())
        {
            if (UTexture2D* Tex = Cast<UTexture2D>(Asset))
            {
                Tex->CompressionSettings = TC_EditorIcon;
                Tex->MarkPackageDirty();
                Tex->PostEditChange();
            }
        }
    }
};

UActorActionUtility — Actor Right-Click Actions

Same pattern for level actors. Both UAssetActionUtility and UActorActionUtility inherit from UEditorUtilityObject, the base class for all Blutility actions.

---

Detail Customizations

Class Customization — IDetailCustomization

class FMyDataAssetCustomization : public IDetailCustomization
{
public:
    static TSharedRef<IDetailCustomization> MakeInstance();
    virtual void CustomizeDetails(IDetailLayoutBuilder& DetailBuilder) override;
    // Override the TSharedPtr overload too — store WeakBuilder for async ForceRefreshDetails
    virtual void CustomizeDetails(const TSharedPtr<IDetailLayoutBuilder>& DetailBuilder) override;
private:
    TWeakPtr<IDetailLayoutBuilder> WeakBuilder;
};
// In CustomizeDetails: EditCategory, AddProperty, AddCustomRow, HideCategory
// Register: PropMod.RegisterCustomClassLayout(UMyClass::StaticClass()->GetFName(), ...MakeInstance)
// Unregister in ShutdownModule: PropMod.UnregisterCustomClassLayout(...)

Struct Customization — IPropertyTypeCustomization

class FMyStructCustomization : public IPropertyTypeCustomization
{
public:
    static TSharedRef<IPropertyTypeCustomization> MakeInstance();
    virtual void CustomizeHeader(TSharedRef<IPropertyHandle> Handle,
        FDetailWidgetRow& HeaderRow, IPropertyTypeCustomizationUtils& Utils) override;
    virtual void CustomizeChildren(TSharedRef<IPropertyHandle> Handle,
        IDetailChildrenBuilder& ChildBuilder, IPropertyTypeCustomizationUtils& Utils) override;
};
// Register: PropMod.RegisterCustomPropertyTypeLayout(FMyStruct::StaticStruct()->GetFName(), ...MakeInstance)

Full implementations, Slate row patterns, IPropertyHandle read/write, NameContent/ValueContent: references/detail-customization-patterns.md

---

Custom Editor Modes

FEdMode (from EdMode.h) provides specialized viewport interaction. Register globally; only one active per viewport at a time.

// MyEditorMode.h
class FMyEditorMode : public FEdMode
{
public:
    static const FEditorModeID EM_MyMode;
    FMyEditorMode();
    virtual void Enter() override;
    virtual void Exit() override;
    virtual bool HandleClick(FEditorViewportClient*, HHitProxy*,
        const FViewportClick&) override;
    virtual bool MouseMove(FEditorViewportClient* ViewportClient,
        FViewport* Viewport, int32 X, int32 Y) override;
    // Use View->DeprojectFVector2D (FSceneView) for world-space ray from pixel coords
    virtual void Render(const FSceneView*, FViewport*,
        FPrimitiveDrawInterface*) override;
    virtual bool UsesToolkits() const override { return true; }
};

// MyEditorMode.cpp
const FEditorModeID FMyEditorMode::EM_MyMode = TEXT("EM_MyEditorMode");

FMyEditorMode::FMyEditorMode()
{
    Info = FEditorModeInfo(EM_MyMode,
        FText::FromString("My Editor Mode"), FSlateIcon(), /*bVisible=*/true);
}

void FMyEditorMode::Enter()
{
    FEdMode::Enter();
    if (!Toolkit.IsValid())
    {
        Toolkit = MakeShareable(new FMyEditorModeToolkit);
        Toolkit->Init(Owner->GetToolkitHost());
    }
}

void FMyEditorMode::Exit()
{
    if (Toolkit.IsValid())
        FToolkitManager::Get().CloseToolkit(Toolkit.ToSharedRef());
    FEdMode::Exit();
}

void FMyEditorMode::Render(const FSceneView* View, FViewport* Viewport,
    FPrimitiveDrawInterface* PDI)
{
    FEdMode::Render(View, Viewport, PDI);
    DrawWireSphere(PDI, FVector::ZeroVector, FLinearColor::Green, 50.f, 16, SDPG_World);
}

Register/unregister in module lifecycle:

// StartupModule
FEditorModeRegistry::Get().RegisterMode<FMyEditorMode>(
    FMyEditorMode::EM_MyMode, FText::FromString("My Mode"), FSlateIcon(), true);
// ShutdownModule
FEditorModeRegistry::Get().UnregisterMode(FMyEditorMode::EM_MyMode);

---

Asset Type Actions

FAssetTypeActions_Base (from AssetTypeActions_Base.h) controls Content Browser appearance and context menu for custom asset types.

class FMyAssetTypeActions : public FAssetTypeActions_Base
{
public:
    virtual FText GetName() const override { return FText::FromString("My Asset"); }
    virtual FColor GetTypeColor() const override { return FColor(200, 100, 50); }
    virtual UClass* GetSupportedClass() const override { return UMyAsset::StaticClass(); }
    virtual uint32 GetCategories() override { return EAssetTypeCategories::Misc; }

    virtual void OpenAssetEditor(const TArray<UObject*>& InObjects,
        TSharedPtr<IToolkitHost> EditWithinLevelEditor) override
    {
        for (UObject* Obj : InObjects)
            if (UMyAsset* Asset = Cast<UMyAsset>(Obj))
                MakeShareable(new FMyAssetEditor)->InitMyEditor(
                    EToolkitMode::Standalone, EditWithinLevelEditor, Asset);
    }
};

Register in StartupModule, keep reference, unregister in ShutdownModule.

FAssetEditorToolkit — Tab-Based Asset Editor Window

class FMyAssetEditor : public FAssetEditorToolkit
{
public:
    void InitMyEditor(EToolkitMode::Type Mode, TSharedPtr<IToolkitHost> Host, UMyAsset* Asset);
    virtual FName GetToolkitFName() const override { return "MyAssetEditor"; }
    virtual FText GetBaseToolkitName() const override { return INVTEXT("My Asset Editor"); }
    virtual void RegisterTabSpawners(const TSharedRef<FTabManager>& TabMgr) override;
    virtual void UnregisterTabSpawners(const TSharedRef<FTabManager>& TabMgr) override;
};
// Call InitAssetEditor() inside InitMyEditor to set up the tab layout via FTabManager::NewLayout

Query open editors programmatically via IAssetEditorInstance:

IAssetEditorInstance* Editor = GEditor->GetEditorSubsystem<UAssetEditorSubsystem>()
    ->FindEditorForAsset(MyAsset, /*bFocusIfOpen=*/false);
if (Editor) Editor->FocusWindow(MyAsset);  // CloseWindow(EAssetEditorCloseReason::AssetEditorHostClosed) — no-arg form deprecated 5.3

Asset Factories

UFactory subclasses allow the Content Browser's "Add" menu to create new custom assets:

UCLASS()
class UMyDataFactory : public UFactory
{
    GENERATED_BODY()
public:
    UMyDataFactory()
    {
        SupportedClass = UMyDataAsset::StaticClass();
        bCreateNew = true;       // appears in "Add" menu
        bEditAfterNew = true;    // opens editor after creation
    }
    virtual UObject* FactoryCreateNew(UClass* InClass, UObject* InParent,
        FName InName, EObjectFlags Flags, UObject* Context,
        FFeedbackContext* Warn) override
    {
        return NewObject<UMyDataAsset>(InParent, InClass, InName, Flags);
    }
};

Custom Thumbnails

UCLASS()
class UMyThumbnailRenderer : public UThumbnailRenderer
{
    GENERATED_BODY()
    virtual void Draw(UObject* Object, int32 X, int32 Y, uint32 Width, uint32 Height,
        FRenderTarget* Target, FCanvas* Canvas, bool bAdditionalViewFamily) override;
};
// Register in module startup:
UThumbnailManager::Get().RegisterCustomRenderer(UMyDataAsset::StaticClass(),
    UMyThumbnailRenderer::StaticClass());

---

Editor Subsystems

UEditorSubsystem (from EditorSubsystem.h) — editor-lifetime singletons, auto-discovered (no registration needed). Access via GEditor->GetEditorSubsystem<T>().

UCLASS()
class MYGAMEEDITOR_API UMyEditorSubsystem : public UEditorSubsystem
{
    GENERATED_BODY()
public:
    virtual void Initialize(FSubsystemCollectionBase& Collection) override
    {
        Super::Initialize(Collection);
        FEditorDelegates::PostUndoRedo.AddUObject(this, &UMyEditorSubsystem::OnPostUndoRedo);
    }
    virtual void Deinitialize() override
    {
        FEditorDelegates::PostUndoRedo.RemoveAll(this);
        Super::Deinitialize();
    }
};

Built-in subsystems:

Subsystem	Purpose
UEditorActorSubsystem	Select, spawn, delete level actors
UEditorAssetSubsystem	Load, save, duplicate assets
ULevelEditorSubsystem	Open, save, manage levels
UEditorUtilitySubsystem	Spawn editor utility widget tabs

---

Menu and Toolbar Extensions (UToolMenus)

UToolMenus (UE5+) replaces FExtender. Register inside the startup callback so Slate is ready:

void FMyGameEditorModule::RegisterMenus()
{
    FToolMenuOwnerScoped OwnerScoped(this);

    // Main menu
    UToolMenu* Menu = UToolMenus::Get()->ExtendMenu("LevelEditor.MainMenu.Window");
    Menu->FindOrAddSection("MyGame").AddMenuEntry("OpenMyPanel",
        FText::FromString("My Panel"), FText::GetEmpty(),
        FSlateIcon(FAppStyle::GetAppStyleSetName(), "Icons.Settings"),
        FUIAction(FExecuteAction::CreateLambda([]() {
            GEditor->GetEditorSubsystem<UEditorUtilitySubsystem>()
                ->SpawnAndRegisterTab(/* WidgetBP */nullptr);
        })));

    // Toolbar button
    UToolMenu* TB = UToolMenus::Get()->ExtendMenu(
        "LevelEditor.LevelEditorToolBar.PlayToolBar");
    TB->FindOrAddSection("MyTools").AddEntry(
        FToolMenuEntry::InitToolBarButton("MyBtn",
            FUIAction(FExecuteAction::CreateLambda([]() {})),
            FText::FromString("My Tool"), FText::GetEmpty(),
            FSlateIcon(FAppStyle::GetAppStyleSetName(), "Icons.Toolbar.Settings")));
}

Always unregister: UToolMenus::UnRegisterStartupCallback(this) + TryGet()->UnregisterOwner(this).

Command Registration — TCommands Pattern

class FMyCommands : public TCommands<FMyCommands>
{
public:
    FMyCommands() : TCommands("MyEditor", INVTEXT("My Editor"), NAME_None, FAppStyle::GetAppStyleSetName()) {}
    virtual void RegisterCommands() override;
    TSharedPtr<FUICommandInfo> OpenPanel;
};
void FMyCommands::RegisterCommands()
{
    UI_COMMAND(OpenPanel, "My Panel", "Opens the panel", EUserInterfaceActionType::Button, FInputChord());
}
// In StartupModule: FMyCommands::Register(); bind via CommandList->MapAction(...)
// In ShutdownModule: FMyCommands::Unregister();

---

Data Validation

// UEditorValidatorBase — auto-discovered by Editor > Tools > Validate Assets
UCLASS()
class UMyValidator : public UEditorValidatorBase
{
    GENERATED_BODY()
    virtual bool CanValidateAsset_Implementation(const FAssetData& InAssetData, UObject* InObject, FDataValidationContext& InContext) const override
    { return InObject && InObject->IsA<UMyDataAsset>(); }
    virtual EDataValidationResult ValidateLoadedAsset_Implementation(
        const FAssetData& InAssetData, UObject* InAsset, FDataValidationContext& Context) override;
};
// Also runnable via commandlet: UnrealEditor-Cmd -run=DataValidation

---

Common Mistakes

Mistake	Fix
Editor headers in Runtime modules	Move to Editor module; use #if WITH_EDITOR for runtime-side editor hooks
No UnregisterCustomClassLayout in ShutdownModule	Always pair register/unregister; crashes Live Coding reload
Raw pointer capture in Slate lambdas	Capture as TWeakPtr; pin before use
LoadingPhase: Default for editor extension module	Use PostEngineInit for modules registering menus or customizations
UEditorUtilityWidget referenced from Runtime	Editor-only; will not exist in packaged builds
ForceRefreshDetails() on every value change	Use only when layout structure changes; use handles/attributes for values
RegisterMode without UnregisterMode	Crashes on plugin reload

---

Related Skills

• ue-ui-umg-slate — Slate widget fundamentals (SNew, TAttribute, FReply, SBox, SHorizontalBox)
• ue-module-build-system — Editor module .Build.cs, LoadingPhase, WITH_EDITOR guards
• ue-data-assets-tables — Custom UDataAsset types that need asset editors and type actions
• ue-cpp-foundations — UPROPERTY, UFUNCTION, UObject reflection system