unreal-object-operation

name	unreal-object-operation
description	Read/write any UObject property (material settings, actor transforms, component configs, etc.), inspect object metadata, find instances, undo/redo. This is the foundational skill for modifying ANY object in Unreal Engine — use it whenever you need to get or set a property on any UObject.

Unreal Object Operations

Operate on UObjects through UCP's call command. This skill covers two function libraries: one available at runtime and one editor-only.

Prerequisite: The unreal-client-protocol skill must be available and the UE editor must be running with the UCP plugin enabled.

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Runtime

UObjectOperationLibrary

CDO Path: /Script/UnrealClientProtocol.Default__ObjectOperationLibrary

Function	Params	Description
GetObjectProperty	ObjectPath, PropertyName	Read a UPROPERTY, returns JSON with property value
SetObjectProperty	ObjectPath, PropertyName, JsonValue	Write a UPROPERTY (supports Undo in editor). JsonValue is a JSON string.
DescribeObject	ObjectPath	Returns class info, all properties (with current values), and all functions
DescribeObjectProperty	ObjectPath, PropertyName	Returns detailed property metadata and current value
DescribeObjectFunction	ObjectPath, FunctionName	Returns full function signature with parameter types
FindObjectInstances	ClassName, Limit (default 100)	Find UObject instances by class path
FindDerivedClasses	ClassName, bRecursive (default true), Limit (default 500)	Find all subclasses of a class
ListComponents	ObjectPath	List all components attached to an actor
FindObjectsByOuter	OuterPath, ClassName (default ""), Limit (default 100)	Find objects owned by a given outer object

Examples

Read a property:

{"object":"/Script/UnrealClientProtocol.Default__ObjectOperationLibrary","function":"GetObjectProperty","params":{"ObjectPath":"/Game/Maps/Main.Main:PersistentLevel.StaticMeshActor_0.StaticMeshComponent0","PropertyName":"RelativeLocation"}}

Write a property:

{"object":"/Script/UnrealClientProtocol.Default__ObjectOperationLibrary","function":"SetObjectProperty","params":{"ObjectPath":"/Game/Maps/Main.Main:PersistentLevel.StaticMeshActor_0.StaticMeshComponent0","PropertyName":"RelativeLocation","JsonValue":"{\"X\":100,\"Y\":200,\"Z\":0}"}}

Find instances:

{"object":"/Script/UnrealClientProtocol.Default__ObjectOperationLibrary","function":"FindObjectInstances","params":{"ClassName":"/Script/Engine.StaticMeshActor","Limit":50}}

Describe an unfamiliar object:

{"object":"/Script/UnrealClientProtocol.Default__ObjectOperationLibrary","function":"DescribeObject","params":{"ObjectPath":"/Game/Maps/Main.Main:PersistentLevel.BP_CustomActor_C_0"}}

List components on an actor:

{"object":"/Script/UnrealClientProtocol.Default__ObjectOperationLibrary","function":"ListComponents","params":{"ObjectPath":"/Game/Maps/Main.Main:PersistentLevel.StaticMeshActor_0"}}

Find objects by outer:

{"object":"/Script/UnrealClientProtocol.Default__ObjectOperationLibrary","function":"FindObjectsByOuter","params":{"OuterPath":"/Game/Maps/Main.Main:PersistentLevel","ClassName":"/Script/Engine.StaticMeshActor","Limit":50}}

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Editor Only

UObjectEditorOperationLibrary

CDO Path: /Script/UnrealClientProtocolEditor.Default__ObjectEditorOperationLibrary

Function	Params	Description
UndoTransaction	Keyword (optional, default "")	Undo the last editor transaction. If Keyword is set, only undoes if the top transaction contains the keyword.
RedoTransaction	Keyword (optional, default "")	Redo the last undone transaction. If Keyword is set, only redoes if the top transaction contains the keyword.
GetTransactionState	(none)	Returns undo/redo stack state: canUndo, canRedo, undoTitle, redoTitle, undoCount, queueLength
ForceReplaceReferences	ReplacementObjectPath, ObjectsToReplacePaths	Redirect all references from the listed objects to the replacement object. ObjectsToReplacePaths is an array of strings.

Examples

Get transaction state:

{"object":"/Script/UnrealClientProtocolEditor.Default__ObjectEditorOperationLibrary","function":"GetTransactionState"}

Undo last transaction (unconditional):

{"object":"/Script/UnrealClientProtocolEditor.Default__ObjectEditorOperationLibrary","function":"UndoTransaction"}

Safe undo (only if top transaction matches):

{"object":"/Script/UnrealClientProtocolEditor.Default__ObjectEditorOperationLibrary","function":"UndoTransaction","params":{"Keyword":"UCP-A1B2C3D4"}}

Force-replace references:

{"object":"/Script/UnrealClientProtocolEditor.Default__ObjectEditorOperationLibrary","function":"ForceReplaceReferences","params":{"ReplacementObjectPath":"/Game/Meshes/NewMesh.NewMesh","ObjectsToReplacePaths":["/Game/Meshes/OldMesh.OldMesh"]}}

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Property Value Formats

When using SetObjectProperty, the JsonValue parameter is a JSON string:

• FVector → "{\"X\":1,\"Y\":2,\"Z\":3}"
• FRotator → "{\"Pitch\":0,\"Yaw\":90,\"Roll\":0}"
• FLinearColor → "{\"R\":1,\"G\":0.5,\"B\":0,\"A\":1}"
• FString → "\"hello\""
• bool → "true" / "false"
• float/int → "1.5" / "42"
• UObject* → "\"/Game/Path/To/Asset.Asset\""

Safe Undo/Redo Pattern

Every UCP call returns an id field (e.g. "UCP-A1B2C3D4") that identifies the Undo transaction. Use this ID as the Keyword parameter when undoing to ensure you only undo your own operations:

1. Make a call → response contains "id":"UCP-A1B2C3D4"
2. If the call produced an undesired result, undo it with UndoTransaction(Keyword="UCP-A1B2C3D4")
3. If the top of the Undo stack is NOT your operation (e.g. user did something manually), the undo will be rejected with an error showing the actual top transaction title.

This prevents accidentally undoing user's manual edits.

When to use Keyword:

• After a failed or undesired operation — pass the ID you just received
• For "try and rollback" patterns — record ID, check result, undo if wrong

When to omit Keyword:

• When the user explicitly asks to undo (they expect any undo)
• When calling GetTransactionState to inspect the stack

Decision Flow

flowchart TD
    A[User request about objects] --> B{Do I know the class and property/function?}
    B -->|YES| C[Build call directly from UE knowledge]
    B -->|NO| D[Call DescribeObject to discover API]
    D --> C
    C --> E[Execute via UCP]
    E --> F{Success?}
    F -->|YES| G[Done]
    F -->|NO| H[Read error + expected, fix and retry]
    H --> E