UnrealMCP C++ Plugin

Unreal Engine 5.5 plugin providing C++ APIs for the Model Context Protocol (MCP) bridge, enabling programmatic control of Unreal Editor operations through JSON commands.

🚀 Quick Start

For interfacing via MCP for your coding agents, go to the Python MCP Server Repository

📋 Features Overview

This MCP plugin provides 35+ commands across 6 categories:

• Blueprint Introspection & Management
• Component Operations & Physics
• Variable & Function Management
• Actor & Level Operations
• Enhanced Input System
• UMG Widget Creation

Core Architecture

UUnrealMCPBridge

The main subsystem that manages MCP communication and command routing.

Public Methods:

• StartServer() - Start the MCP TCP server
• StopServer() - Stop the MCP server
• IsRunning() - Check if server is active
• ExecuteCommand(CommandType, Params) - Execute a command with JSON parameters

Command APIs

Editor Commands

Level and actor management operations.

Available Commands:

• get_actors_in_level - List all actors in current level
• find_actors_by_name - Find actors by name pattern
• spawn_actor - Create new actors with transform
• delete_actor - Remove actors from level
• set_actor_transform - Modify actor position, rotation, scale
• get_actor_properties - Retrieve actor property values
• set_actor_property - Set actor property values
• focus_viewport - Focus camera on specific targets
• take_screenshot - Capture viewport screenshots

Blueprint Commands

Comprehensive blueprint introspection, creation, and modification.

Blueprint Introspection:

• list_blueprints - List all blueprints in directory
• blueprint_exists - Check if blueprint exists
• get_blueprint_info - Get comprehensive blueprint metadata
• get_blueprint_path - Get blueprint asset path
• get_blueprint_components - List all blueprint components
• get_blueprint_variables - List all variables with types
• get_blueprint_functions - List all custom functions
• get_component_hierarchy - Get component parent-child tree

Blueprint Asset Management:

• create_blueprint - Create new Blueprint classes
• delete_blueprint - Delete blueprint assets
• duplicate_blueprint - Clone blueprints with new name
• compile_blueprint - Compile Blueprint assets
• spawn_blueprint_actor - Spawn Blueprint actors in level

Variable Management:

• remove_variable - Delete variables
• rename_variable - Rename variables with reference updates
• set_variable_default_value - Set default values (bool, int, float, string, Vector, Rotator)
• set_variable_metadata - Configure variable metadata (tooltip, category, visibility)

Function Management:

• add_function - Create custom functions
• remove_function - Delete functions
• add_function_parameter - Add parameters to functions
• set_function_return_type - Configure return value type
• set_function_metadata - Configure function metadata (category, tooltip, pure)

Component Management:

• add_component_to_blueprint - Add components to Blueprints
• remove_component - Delete components
• rename_component - Rename components
• set_component_transform - Update component transform
• set_component_property - Set component property values
• set_physics_properties - Configure physics simulation
• set_static_mesh_properties - Configure static mesh components
• set_pawn_properties - Configure pawn-specific properties
• get_component_properties - Get detailed component properties

Blueprint Node Commands

Visual scripting node operations.

Available Commands:

• connect_blueprint_nodes - Connect Blueprint graph nodes
• add_blueprint_self_reference - Add self reference nodes
• add_blueprint_get_self_component_reference - Add component reference nodes
• find_blueprint_nodes - Search for specific nodes
• add_blueprint_event_node - Add event nodes
• add_blueprint_input_action_node - Add input action nodes
• add_blueprint_function_node - Add function call nodes
• add_blueprint_variable - Create variable nodes

Input Commands

Enhanced input system management.

Available Commands:

• create_enhanced_input_action - Create enhanced input actions
• create_input_mapping_context - Create input mapping contexts
• add_enhanced_input_mapping - Add mappings to contexts
• apply_mapping_context - Apply contexts at runtime
• remove_mapping_context - Remove contexts at runtime
• clear_all_mapping_contexts - Clear all active contexts

Registry & Query Commands

Dynamic discovery of available classes and types.

Available Commands:

• get_supported_parent_classes - Query all available parent classes (100+ via reflection)
• get_supported_component_types - Query all available component types (50+ via reflection)
• get_available_api_methods - Get list of all API methods organized by category

UMG Widget Commands

User interface widget creation and management.

Available Commands:

• create_umg_widget_blueprint - Create widget blueprints
• add_text_block_to_widget - Add text elements
• add_button_to_widget - Add interactive buttons
• bind_widget_event - Bind widget events to functions
• add_widget_to_viewport - Display widgets in game
• set_text_block_binding - Bind text to data properties

Data Types

Core Parameter Structures

All commands use strongly-typed parameter structures defined in Core/MCPTypes.h:

• FBlueprintCreationParams - Blueprint creation parameters
• FBlueprintSpawnParams - Blueprint actor spawning
• FComponentParams - Component addition parameters
• FPropertyParams - Property modification parameters
• FPhysicsParams - Physics configuration
• FStaticMeshParams - Static mesh setup
• FWidgetCreationParams - Widget creation
• FTextBlockParams - Text block configuration
• FButtonParams - Button configuration
• FWidgetEventBindingParams - Event binding
• FInputActionParams - Input action creation
• FInputMappingContextParams - Mapping context setup

Result Types

All operations return TResult<T> types for error handling:

• Success operations return wrapped values
• Failed operations return descriptive error messages

Integration

MCP Protocol

This plugin implements the Model Context Protocol (MCP) for JSON-based command/response communication. The Python MCP server provides the interface for coding agents to access these capabilities.

Python MCP Repository: sengokudaikon/unreal-mcp

Command Registration

Commands are registered using a registry pattern in each command handler class:

// Example from FUnrealMCPEditorCommands
CommandHandlers.Add(TEXT("spawn_actor"), &FSpawnActor::Handle);

Parameter Parsing

All command handlers parse JSON parameters using the FromJson static methods on parameter structures:

auto Result = FSpawnParams::FromJson(Params);
if (!Result.IsSuccess()) {
    return CreateErrorResult(Result.GetError());
}

Error Handling

Consistent error handling across all commands using the Result<T> pattern:

• Validation errors return immediately
• Runtime errors are logged and returned
• Success responses contain operation results

Services

ActorService

High-level actor management operations with validation and error handling.

BlueprintService

Blueprint asset operations including creation, compilation, and modification.

BlueprintGraphService

Visual scripting node manipulation and graph management.

InputService

Enhanced input system integration and management.

ViewportService

Viewport control and screenshot capabilities.

WidgetService

UMG widget creation and runtime management.

Usage Pattern

Commands are executed through the bridge subsystem:

// Get bridge instance
UUnrealMCPBridge* Bridge = GEditor->GetEditorSubsystem<UUnrealMCPBridge>();

// Create JSON parameters
TSharedPtr<FJsonObject> Params = MakeShared<FJsonObject>();
Params->SetStringField(TEXT("actor_name"), TEXT("MyActor"));

// Execute command
TSharedPtr<FJsonObject> Result = Bridge->ExecuteCommand(TEXT("spawn_actor"), Params);

Getting Started

1. Install this plugin in your Unreal Engine project
2. Deploy the Python MCP Server from sengokudaikon/unreal-mcp
3. Connect your coding agent to the MCP server to access all blueprint and editor operations
4. Use available commands to manipulate blueprints, actors, and game content programmatically