unreal-engine-mcp

# Unreal Engine MCP [](https://github.com/FFZackFair92/unreal-engine-mcp/actions/workflows/ci.yml) [](https://www.python.org/) [](LICENSE) [Italiano](README.it.md) An [MCP](https://modelcontextprotocol.io) server that lets an AI agent drive Unreal Engine 5: create projects, import assets, build levels and Blueprints, configure replication, compile C++, run Play In Editor and package the game. **No C++ plugin to compile.** It uses two plugins that already ship with the engine — *Python Editor Script Plugin* and *Remote Control API* — and talks to the editor over local HTTP. ``` ┌─ LOCAL layer ── processes + public HTTP │ UnrealEditor.exe, UnrealBuildTool, RunUAT, asset downloads Agent ──stdio──▶ MCP │ └─ EDITOR layer ── HTTP :30010 (Remote Control API) └─ ExecutePythonCommandEx → running editor ``` The local layer exists because the Remote Control API only works against an editor that is **already running**: creating a project, launching it, compiling and packaging all have to happen at the process level. - **68 tools** and **5 resources** — [full reference](docs/TOOLS.md) - **212 tests**, none of which need Unreal installed - **[Unreal automation notes](docs/UNREAL-NOTES.md)** — the API traps found the hard way --- ## Requirements - Unreal Engine **5.0 or newer** (developed and tested against 5.8 — see [version compatibility](#unreal-version-compatibility)) - Python 3.10+ - Windows, Linux or macOS. Development happens on Windows, which is where the local layer is exercised most; the Linux and macOS paths (`Build.sh`, `RunUAT.sh`, `pgrep`) are implemented and covered by CI, but less battle-tested. The editor layer is platform-neutral. ### Unreal version compatibility The server detects what the running engine supports at startup of each call — `ue_status` reports it under `capabilities` — and fails with an explicit message instead of a cryptic Python error when a feature is missing: | Feature | Works on | |---|---| | Actors, levels, spawn/transform, PIE, project settings, build & packaging, Sound Cues | **5.0+** | | Blueprint creation, components (`SubobjectDataSubsystem`), reparenting | **5.0+** | | Materials, material instances, screenshots, C++ class generation | **5.0+** | | glTF/`.glb` import via Interchange | **5.2+** (earlier: enable the *glTF Importer* plugin; the tool tells you when that is the problem) | | Blueprint member variables + per-variable replication (`ue_add_variable`) | **5.4+** (no Python API before that — the tool says so explicitly) | | MetaSounds | any 5.x with the *MetaSound* plugin enabled | Custom engine builds are fine: detection is based on the actual Python API surface, not on the version number. ## Install ```bash pip install unreal-engine-mcp ``` Or run it without installing anything, if you have [uv](https://docs.astral.sh/uv/): ```bash uvx unreal-engine-mcp ``` Or from source, to hack on it: ```bash git clone https://github.com/FFZackFair92/unreal-engine-mcp.git cd unreal-engine-mcp pip install -e . ``` ## Connect it to your client The server speaks standard MCP over stdio, so **any MCP-capable client works** — Claude, Cursor, VS Code, Windsurf, OpenAI Codex, custom agents. The command is always the same; only where the config lives differs. ### Claude Desktop / Cowork `Settings ▸ Developer ▸ Edit Config`, then add to `mcpServers`: ```json { "mcpServers": { "unreal-mcp": { "command": "python", "args": ["-m", "unreal_mcp.server"], "env": { "UE_MCP_PORT": "30010" } } } } ``` ### Claude Code ```bash claude mcp add unreal-mcp -- python -m unreal_mcp.server ``` ### Cursor `~/.cursor/mcp.json` (global) or `.cursor/mcp.json` in the project — same JSON shape as Claude Desktop (`mcpServers` root key). ### VS Code (Copilot agent mode) `.vscode/mcp.json` — note the root key is `servers` here: ```json { "servers": { "unreal-mcp": { "type": "stdio", "command": "python", "args": ["-m", "unreal_mcp.server"] } } } ``` ### Windsurf `~/.codeium/windsurf/mcp_config.json` — same `mcpServers` shape as Claude Desktop. ### OpenAI Codex CLI `~/.codex/config.toml`: ```toml [mcp_servers.unreal-mcp] command = "python" args = ["-m", "unreal_mcp.server"] ``` ### OpenAI Agents SDK (custom agents) ```python from agents.mcp import MCPServerStdio unreal = MCPServerStdio(params={"command": "python", "args": ["-m", "unreal_mcp.server"]}) ``` Restart the client completely after editing its config. In every case `python` must be the interpreter where you ran `pip install -e .` — use an absolute path if in doubt. > **Note:** ChatGPT's connector UI only accepts *remote* MCP servers. This > server is stdio/local by design (it drives processes on your machine), so use > it from clients with stdio support — the ones above — or wrap it with an > MCP proxy if you really need HTTP. ## Set up the Unreal side ### Starter project — zero setup, zero builds Copy [`StarterProject/`](StarterProject/) wherever you like and open the `.uproject` with any UE 5.0+: plugins enabled, security config in place, web server auto-started. Being Blueprint-only with engine plugins, **there is nothing to compile** — unlike starters that bundle a C++ plugin. ### New project — nothing to do by hand Ask the agent to run `ue_project_create`. It writes the `.uproject` with the required plugins enabled, the security flags Remote Control needs, and an `init_unreal.py` that starts the web server on every editor launch. ``` ue_engine_list → ue_project_create → ue_editor_open → ue_status ``` ### Existing project — two steps 1. **Enable the plugin**: `Edit ▸ Plugins` → *Python Editor Script Plugin*. Restart when prompted. 2. **Tick one box**: `Edit ▸ Project Settings` → search *Python* → check **Enable Remote Execution**. That is the whole setup. The server discovers the editor over the engine's own Python remote execution channel — no config file, no HTTP port. <details> <summary>The HTTP route (Remote Control API), for when multicast will not do</summary> The native channel finds the editor with a UDP multicast ping on the local machine. That is the easy path, but it does not cross a subnet, and some corporate networks and VPN adapters swallow multicast entirely. In those cases — or with the editor on **another machine** — use the Remote Control API instead, with `UE_MCP_TRANSPORT=remotecontrol`. 1. **Enable the plugins**: *Python Editor Script Plugin* and *Remote Control API*. Restart when prompted. 2. **Allow remote Python.** Create `Config/DefaultRemoteControl.ini`: ```ini [/Script/RemoteControlCommon.RemoteControlSettings] bAutoStartWebServer=True bAutoStartWebSocketServer=True RemoteControlHttpServerPort=30010 bEnableRemotePythonExecution=True bAllowAnyRemoteFunctionCall=False +CustomAllowedRemoteFunctionCalls=(ClassPath="/Script/PythonScriptPlugin.PythonScriptLibrary") bAllowConsoleCommandRemoteExecution=False ``` These are **two separate gates** — one unlocks the object, the other the function call — and they fail with different errors. `DefaultEngine.ini` is the wrong file: `URemoteControlSettings` is declared `UCLASS(config = RemoteControl)`. Restart the editor. On engines that predate some of these keys they are simply ignored — older versions did not gate those calls in the first place. The server listens on `127.0.0.1` only, so remote Python execution is not reachable from outside the machine. What the server can do once connected, and how to open it up safely if you really need to reach the editor from another machine, is in [SECURITY.md](SECURITY.md). `bAllowConsoleCommandRemoteExecution` stays **off**. It enables `ExecuteConsoleCommand` *through the web API*, which this server never calls — the console commands it does need (`LiveCoding.Compile`, `WebControl.StartServer`, `HighResShot`) are issued from inside Python via `unreal.SystemLibrary.execute_console_command` and do not go through that gate. Older versions of this project set it to `True`; existing projects can flip it to `False` without losing anything. 3. **Check it**: open `http://127.0.0.1:30010/remote/info` in a browser. JSON back means you are connected. </details> ### Which transport is in use `ue_status` reports it. By default (`UE_MCP_TRANSPORT=auto`) the server tries the native channel first and falls back to HTTP, so a project set up either way just works. Set `pyremote` or `remotecontrol` to pin one. ## What it can do | Area | Highlights | |---|---| | **Projects** | Find engine installs, create projects from a spec, manage plugins | | **Editor lifecycle** | Open (waiting for the bridge), status, clean shutdown | | **C++** | Generate compilable classes with the boilerplate written correctly, then reparent Blueprints onto them | | **Build** | Compile C++ in the background; `ue_live_compile` recompiles **with the editor open** via Live Coding | | **Package** | `RunUAT BuildCookRun` → standalone executable, with phase reporting | | **Assets** | Import `.glb`/`.gltf`/`.fbx`/`.wav`, list and search the Content Browser | | **Levels** | Create and open levels, spawn/move/delete actors, batch spawn, set properties on placed actors | | **Materials** | Build material graphs, wire PBR textures, material instances, assign to actors | | **Blueprints** | Create, add components, typed variables with replication, class defaults, reparent, compile | | **Networking** | Replication flags, multi-client PIE, project settings | | **Audio** | Import wavs, MetaSound sources, Sound Cues | | **Free assets** | Poly Haven, ambientCG and Kenney downloads (all CC0), plus any direct URL | | **Feedback** | `ue_screenshot` captures the viewport, so the agent can see what it built | Full parameter list in [docs/TOOLS.md](docs/TOOLS.md). ### Working around the Blueprint graph limit **Blueprint node graphs cannot be authored from Python.** `EdGraph.Nodes` is protected, pins are not exposed and there is no linking API — this is a hard limit of the engine, not of this server. Details in [docs/UNREAL-NOTES.md](docs/UNREAL-NOTES.md). What works instead: **put the logic in a C++ parent class.** The Blueprint stays the container for components and tweakable values; the behaviour is inherited. ``` ue_cpp_class_create # writes the class, and the whole C++ module if the # project was Blueprint-only ue_editor_close ue_build_start # poll ue_build_status until running=false ue_editor_open ue_reparent_blueprint # the Blueprint now inherits the behaviour ``` Blueprint variables whose names match a `UPROPERTY` on the new parent are absorbed by it, so values set in the editor survive the move. Functions marked `BlueprintCallable` become callable from the graph — an agent can build the vocabulary the designer then wires up by hand. Material graphs, unlike Blueprint graphs, *are* fully scriptable: `ue_create_material` really does create and connect the nodes. ### Other limits - **Compiling C++ needs the editor closed**, unless the change only touches function bodies — then `ue_live_compile` works with it open. - **Packaging always needs the editor closed**: the build step rewrites the DLLs the editor holds in memory. - **Feature availability varies with the engine version** — see the [compatibility table](#unreal-version-compatibility); `ue_status` reports what the running engine supports. - **Fab/Marketplace content** has no public API. Those tools shell out to the community client [`legendary`](https://github.com/derrod/legendary). ## Configuration | Variable | Default | Purpose | |---|---|---| | `UE_MCP_TRANSPORT` | `auto` | `auto`, `pyremote` (native channel) or `remotecontrol` (HTTP) | | `UE_MCP_HOST` / `UE_MCP_PORT` | `127.0.0.1` / `30010` | Remote Control endpoint | | `UE_MCP_TIMEOUT` | `180` | Per-call timeout in seconds | | `UE_MCP_PROJECT` | — | Which project to drive when several editors are open | | `UE_MCP_MULTICAST_GROUP` / `_PORT` | `239.0.0.1` / `6766` | Discovery endpoint for the native channel | | `UE_MCP_MULTICAST_BIND` | `0.0.0.0` | Interface the discovery ping goes out of — set it when several adapters (VPN, WSL, Hyper-V) hide the editor | | `UE_MCP_MULTICAST_TTL` | `0` | Keeps discovery on this machine. Raising it exposes arbitrary code execution to the network | | `UE_MCP_ENGINE_DIRS` | — | Extra folders to search for engine installs | | `UE_MCP_LIBRARY` | `~/UnrealAssetLibrary` | Where downloaded assets land | | `UE_MCP_MAX_DOWNLOAD` | 4 GiB | Per-file download cap | If the engine sits somewhere unusual, you can also drop an `mcp_engine.txt` next to the `.uproject` containing its path, or pass `engine_root` explicitly. ## Development The test suite runs **without Unreal installed**: `tests/fake_unreal.py` stands in for the `unreal` module and `tests/fake_server.py` emulates the Remote Control API while *actually executing* the generated snippets — so the whole chain tool → snippet → harness → result is covered. ```bash pip install -e ".[dev]" pytest -q ``` Adding a tool: a reusable helper in `src/unreal_mcp/ue_side.py` (editor side), an `@mcp.tool()` function in `server.py`, and a test in `tests/`. See [CONTRIBUTING.md](CONTRIBUTING.md) for the conventions worth knowing. `ue_side.py` is installed into the running editor as a module and keyed by a hash of its source, so editor-side changes take effect on the next call without restarting the server — and every other call is just a small snippet that imports it. Changes to `server.py` or `local.py` need a client restart. ## Troubleshooting | Symptom | Cause | |---|---| | `No response from http://127.0.0.1:30010` | Editor closed, or the web server never started → console: `WebControl.StartServer` | | `Object Default__PythonScriptLibrary cannot be accessed remotely` | Missing `bEnableRemotePythonExecution` in `DefaultRemoteControl.ini` | | `Executing function 'ExecutePythonCommandEx' is not allowed` | Missing `CustomAllowedRemoteFunctionCalls` entry | | `404 on /remote/object/call` | *Remote Control API* plugin not enabled | | `NameError: name 'unreal' is not defined` | *Python Editor Script Plugin* not enabled | | `Unable to build while Live Coding is active` | `LiveCodingConsole.exe` outlives the editor — kill it (the build tools do this automatically) | | `No Unreal Engine installation found` | Set `UE_MCP_ENGINE_DIRS`, add `mcp_engine.txt`, or pass `engine_root` | | `ModuleNotFoundError: No module named 'mcp.server.fastmcp'` | `mcp` 2.x is installed; this server targets the 1.x line. `pip install "mcp<2"` — reinstalling the package does it for you | ## Licence MIT — see [LICENSE](LICENSE). ## References - [Remote Control for Unreal Engine](https://dev.epicgames.com/documentation/en-us/unreal-engine/remote-control-for-unreal-engine) - [Remote Control Quick Start](https://dev.epicgames.com/documentation/en-us/unreal-engine/remote-control-quick-start-for-unreal-engine) - [Importing glTF files](https://dev.epicgames.com/documentation/en-us/unreal-engine/importing-gltf-files-into-unreal-engine) - [Poly Haven API](https://github.com/Poly-Haven/Public-API) · [ambientCG API](https://docs.ambientcg.com/api/v2/full_json/)