UEBridgeMCP

Native C++ Model Context Protocol (MCP) plugin for Unreal Engine 5.6+

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Overview

UEBridgeMCP is a native C++ Unreal Engine plugin that exposes the Unreal Editor to any MCP-compatible AI client over Streamable HTTP. It embeds the MCP server directly inside the editor process, so tools can inspect and edit Blueprints, levels, assets, materials, widgets, StateTrees, PIE sessions, and build workflows without a separate bridge process.

Acknowledgments: This project is a heavily extended and optimized fork of yes-ue-mcp by softdaddy-o. Special thanks to the original author for the foundational MCP HTTP server architecture.

Current release: v1.19.0

Highlights:

• Native UE integration - uses Unreal's built-in HTTP stack and editor APIs
• 46 built-in tools - the authoritative list lives in Source/UEBridgeMCPEditor/Private/UEBridgeMCPEditor.cpp
• Cross-client compatible - works with Claude Code, Claude Desktop, Cursor, Continue, Windsurf, and other MCP clients
• Project-agnostic - no game-specific coupling; can be moved between UE 5.6+ C++ projects
• Extensible - add custom tools by subclassing UMcpToolBase

Documentation Map

Document	Description
Tools Reference	Full list of the built-in tools, grouped by workflow and subsystem
Tool Development	How to implement, register, validate, and maintain your own MCP tools
Troubleshooting	Known failure modes, connection issues, PIE caveats, and debugging steps
Architecture	Module layout, request lifecycle, registry warmup, and threading model
Chinese Documentation Index	Chinese landing page with links to the translated docs

Quick Start

Requirements

• Unreal Engine 5.6+
• A C++ Unreal project (Blueprint-only projects should be converted by adding any C++ class)
• Core plugin dependencies enabled in UEBridgeMCP.uplugin:
  • EditorScriptingUtilities
  • GameplayAbilities
  • StateTree
  • GameplayStateTree
• PythonScriptPlugin powers run-python-script. The plugin descriptor marks it optional, but the current source build links against it directly in Source/UEBridgeMCPEditor/UEBridgeMCPEditor.Build.cs, so keep it enabled unless you intentionally remove Python tooling.

Installation

1. Copy the plugin into your project:

<YourProject>/Plugins/UEBridgeMCP/

2. Enable it in your .uproject:

{
  "Plugins": [
    { "Name": "UEBridgeMCP", "Enabled": true }
  ]
}

3. Regenerate project files and build your editor target.
4. Launch the editor and confirm the module loads successfully.

Configuration

Server settings live in Config/DefaultUEBridgeMCP.ini:

[/Script/UEBridgeMCPEditor.McpServerSettings]
ServerPort=8080
bAutoStartServer=true
BindAddress=127.0.0.1
LogLevel=Log

Important: on Windows, prefer 127.0.0.1 instead of localhost. Some clients resolve localhost to IPv6 ([::1]) while the server commonly binds IPv4, which causes avoidable connection failures.

Client Configuration

Any MCP client that supports HTTP transport can connect. Examples:

Claude Code CLI

claude mcp add --transport http unreal-engine http://127.0.0.1:8080/mcp

Claude Desktop (claude_desktop_config.json)

{
  "mcpServers": {
    "unreal-engine": {
      "url": "http://127.0.0.1:8080/mcp"
    }
  }
}

Cursor (.cursor/mcp.json)

{
  "mcpServers": {
    "unreal-engine": {
      "url": "http://127.0.0.1:8080/mcp"
    }
  }
}

VS Code Continue (.continue/config.json)

{
  "mcpServers": [
    {
      "name": "unreal-engine",
      "transport": {
        "type": "http",
        "url": "http://127.0.0.1:8080/mcp"
      }
    }
  ]
}

Sanity Check

Use a tools/list request to confirm the server is reachable:

curl -s -X POST http://127.0.0.1:8080/mcp \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}'

If the plugin is running correctly, the response should contain the registered tool set for the current editor session.

Built-in Tool Surface

The authoritative registration site is:

Source/UEBridgeMCPEditor/Private/UEBridgeMCPEditor.cpp

At v1.19.0, the plugin registers 46 built-in tools across the following groups:

Group	Count	Examples
Query and inspection	15	query-blueprint-summary, query-asset, get-asset-diff, find-references, get-logs
Creation and editing	14	create-asset, add-widget, edit-blueprint-graph, edit-level-batch, apply-material
StateTree	5	query-statetree, add-statetree-state, add-statetree-transition
PIE, scripting, build, and RPC	8	run-python-script, trigger-live-coding, pie-session, pie-input, wait-for-world-condition, call-function
High-level orchestration	4	blueprint-scaffold-from-spec, query-gameplay-state, auto-fix-blueprint-compile-errors, generate-level-structure

See Tools Reference for the full list and per-tool summaries.

Architecture Snapshot

MCP Client
  -> HTTP POST /mcp
  -> UEBridgeMCPEditor module
  -> FMcpServer
  -> FMcpToolRegistry
  -> UMcpToolBase-derived tools
  -> Unreal Editor subsystems / assets / worlds / PIE

The plugin ships two modules:

• UEBridgeMCP - runtime protocol types, schema helpers, base classes, and tool registry
• UEBridgeMCPEditor - editor-only server, subsystem integration, built-in tools, and toolbar/status integration

See Architecture for the full lifecycle, warmup behavior, and threading constraints.

Extending UEBridgeMCP

To add a new tool:

1. Create a new UMcpToolBase subclass under Source/UEBridgeMCPEditor/Public/Tools/ and Private/Tools/
2. Override GetToolName, GetToolDescription, GetInputSchema, GetRequiredParams, and Execute
3. Register the class in FUEBridgeMCPEditorModule::RegisterBuiltInTools()
4. Rebuild or trigger Live Coding
5. Add automated validation if your branch or repo contains a test harness; otherwise document a focused live-editor validation recipe such as a tools/list or tools/call request

See Tool Development for a fuller guide and recommended implementation rules.

Versioning

UEBridgeMCP follows semantic versioning for public releases.

• Keep VersionName in UEBridgeMCP.uplugin and UEBRIDGEMCP_VERSION in Source/UEBridgeMCP/Public/UEBridgeMCP.h identical.
• Bump both in the same PR when public tool names, schemas, defaults, or externally visible behavior changes.
• Update CHANGELOG.md and RELEASE_NOTES.md alongside the version bump.

Troubleshooting Entry Points

Start with Troubleshooting if you hit any of these problems:

• The client cannot connect to http://127.0.0.1:8080/mcp
• tools/list is empty or missing expected tools
• PIE start/stop appears stuck
• Python execution fails or crashes the editor
• Live Coding or rebuild operations do not reflect recent code changes
• Multiple UE projects are fighting over the same server port

License

GNU General Public License v3.0 - see LICENSE for details.

Links

• GitHub Repository
• Changelog
• Release Notes
• MCP Overview
• MCP Specification
• Unreal Engine Documentation

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