Godot MCP is an AI-powered game development assistant for the Godot Editor. Connect Claude, Cursor, Copilot, or any MCP-aware agent to Godot and let it inspect and drive your project — create nodes, edit scenes, manage resources and scripts, capture screenshots, and more.

Godot-MCP is the Godot counterpart of Unity-MCP: a C# editor addon that exposes Godot Editor operations as AI Tools and connects them to an MCP server through the same hosted cloud backend (ai-game.dev) that powers Unity-MCP — or your own self-hosted server. The MCP / reflection stack is not forked: it is shared with Unity-MCP and consumed from nuget.org as PackageReferences.

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• ✔️ AI agents — Use the best agents from Anthropic, OpenAI, Google, or any other provider with no vendor lock-in
• ✔️ 39 built-in Tools — A wide range of MCP Tools across 11 families for operating the Godot Editor
• ✔️ C# & GDScript — Read, create, and update both .cs and .gd scripts, and attach them to nodes
• ✔️ Scene & Node control — Build and edit the scene tree, open/save .tscn scenes, mutate .tres/.res resources
• ✔️ Visual feedback — Capture viewport, camera, and isolated-node screenshots the LLM can inspect
• ✔️ Reflection escape hatch — Find and call any C# method across loaded assemblies via ReflectorNet
• ✔️ Cloud or self-hosted — Connect to ai-game.dev out of the box, or point at your own server
• ✔️ Natural conversation — Chat with AI like you would with a human

Quick Start

Get up and running from a terminal using the godot-cli (the Godot analog of unity-mcp-cli) — no manual file copying or csproj editing required:

# 1. Install godot-cli
npm install -g godot-cli

# 2. (Optional) Scaffold a fresh Godot C# project — skip if you already have one
godot-cli create-project --dotnet ./MyGodotProject

# 3. Install the godot_mcp addon: downloads addons/godot_mcp/ from the matching
#    GitHub release, adds the required NuGet packages to your .csproj, and enables
#    the plugin in project.godot — all idempotently
godot-cli install-plugin ./MyGodotProject

# 4. Pick an AI agent (Claude Code, Cursor, Copilot, …) and write its MCP config
godot-cli setup-mcp claude-code ./MyGodotProject

# 5. Open the Godot editor — builds the C# assembly first (so the addon loads on
#    the very first open) then auto-connects with the right GODOT_MCP_* env vars
godot-cli open ./MyGodotProject

# 6. Wait until the plugin answers the readiness probe
godot-cli wait-for-ready ./MyGodotProject

That's it. Ask your AI "Create 3 cubes in a circle with radius 2" and watch it happen. ✨

Offline / dev install: install-plugin --source <path-to>/addons/godot_mcp copies the addon from a local directory instead of downloading it. Prefer the matching release version with install-plugin --version <x.y.z> if you need a specific addon build. The manual route (copy the addon + add the NuGet packages yourself) is still documented under Installation Steps 1–2 for the Asset Library / hand-managed flows.

See the full CLI documentation for every command, editor-resolution order, and connection env vars.

Contents

• Quick Start
• Tools Reference
• Requirements
• Installation
  • Step 1: Add the addon
    • Option A — Godot Asset Library (recommended)
    • Option B — GitHub Release zip
    • Option C — copy from source
  • Step 2: Add the NuGet packages
  • Step 3: Install an AI agent
• Connect
  • Cloud mode (default) — ai-game.dev
  • Custom mode — your own server
• Godot MCP Server setup
  • Local server — let the addon download & run it for you
  • Build & run the server manually (advanced)
• Customize Tools
• Runtime usage (in-game)
  • Capturing in-game runtime errors
  • Sample: a live game-state tool
  • Where the server URL and token come from
  • Security: opt-in only, default OFF
• How Godot MCP Architecture Works
• Building & contributing
• License

Tools Reference

Godot-MCP ships 39 built-in tools grouped into 11 families. Tool names mirror Unity-MCP where sensible (scene-*, node-*, …). Every tool returns a structured, ReflectorNet-serialized result (or a PNG image for screenshots). All editor tools are available immediately after the addon is enabled — no extra configuration required. The runtime-errors family is the exception: it surfaces errors from the running game and is OFF by default — opt in with builder.WithRuntimeErrorCapture() (see Capturing in-game runtime errors).

Family	Tools	What it does
ping	ping	Lightweight readiness probe — echoes a message back, or returns pong. Verifies the end-to-end MCP path (editor → SignalR → tool dispatch).
node	node-find, node-create, node-modify, node-set-parent, node-duplicate, node-delete	Inspect and edit the active scene tree (the Godot analog of Unity GameObjects), driving EditorInterface on the main thread.
scene	scene-open, scene-save, scene-create, scene-list-opened, scene-get-data	Open, save, create, and inspect Godot scenes (res://*.tscn PackedScenes) in the editor.
resource	resource-find, resource-get-data, resource-modify, resource-create, resource-move, resource-delete	Find and mutate Godot resources (.tres/.res) through ResourceLoader/ResourceSaver/EditorFileSystem, keeping .import sidecars consistent.
filesystem	filesystem-list, filesystem-reimport	Browse and reimport the project's res:// tree via the editor EditorFileSystem index (file types + uids without loading resources).
script	script-read, script-create, script-update, script-delete, script-attach-to-node, script-validate	CRUD on C# (.cs) and GDScript (.gd) files, plus attaching a script to a node and validating GDScript.
screenshot	screenshot-viewport, screenshot-camera, screenshot-isolated	Capture the editor viewport, a specific camera, or an isolated node render, returned as a PNG image the LLM can inspect.
editor	editor-application-get-state, editor-application-set-state, editor-selection-get, editor-selection-set	Read/drive the editor run-and-play lifecycle (Godot launches the game in a separate process) and the current selection.
console	console-get-logs, console-clear-logs	Read and clear the plugin's editor log collector (GD.Print/GD.PushWarning/GD.PushError).
reflection	reflection-method-find, reflection-method-call	Find and call C# methods (static/instance, public/private) across every loaded assembly via ReflectorNet — the engine-agnostic escape hatch.
runtime-errors	runtime-errors-get, runtime-errors-clear	Poll errors raised inside the running game (NOT the editor) — GDScript runtime errors, push_error/push_warning, shader errors, and C# unhandled / unobserved-Task exceptions, with multi-frame GDScript backtraces on Godot 4.5+. OFF by default — opt in with builder.WithRuntimeErrorCapture().

ping

• ping — Lightweight readiness probe; echoes a message back, or returns pong.

node

• node-find — Find nodes in the active scene tree by path, type, or name.
• node-create — Create a new node under a parent (optionally instancing a .tscn sub-scene).
• node-modify — Set fields/properties on one or more nodes.
• node-set-parent — Reparent nodes within the scene tree.
• node-duplicate — Duplicate nodes together with their subtrees.
• node-delete — Delete nodes from the active scene.

scene

• scene-open — Open a res://*.tscn PackedScene in the editor.
• scene-save — Save an open scene back to its .tscn file.
• scene-create — Create a new scene asset in the project.
• scene-list-opened — List the scenes currently open in the editor.
• scene-get-data — Retrieve the root nodes / structure of a scene.

resource

• resource-find — Search the project for resources (.tres/.res).
• resource-get-data — Read a resource's serialized fields and properties.
• resource-modify — Modify a resource's properties.
• resource-create — Create a new resource asset.
• resource-move — Move / rename a resource, keeping .import sidecars consistent.
• resource-delete — Delete a resource from the project.

filesystem

• filesystem-list — Browse the res:// tree (file types + uids) via the editor file index.
• filesystem-reimport — Reimport files in the project.

script

• script-read — Read a .cs / .gd script file.
• script-create — Create a new script file.
• script-update — Update an existing script file's contents.
• script-delete — Delete a script file.
• script-attach-to-node — Attach a script to a node.
• script-validate — Validate GDScript (.gd) files and return structured parse/compile diagnostics.

screenshot

• screenshot-viewport — Capture the editor viewport as a PNG.
• screenshot-camera — Capture from a specific camera.
• screenshot-isolated — Render a node in isolation from a chosen angle.

editor

• editor-application-get-state — Read the editor application/run state.
• editor-application-set-state — Start / stop the running game.
• editor-selection-get — Get the current editor selection.
• editor-selection-set — Set the current editor selection.

console

• console-get-logs — Read the plugin's collected editor logs (with filtering). This includes the plugin's connection lifecycle diagnostics (connect/disconnect, drain-timeout, config save/load, skill-gen, dev-control, dispatcher, and runtime-capture warnings), which route through the same capture sink as its framework logs.
• console-clear-logs — Clear the collected log cache.

reflection

• reflection-method-find — Find C# methods (including private) across every loaded assembly.
• reflection-method-call — Call any C# method with input parameters and get the result.

runtime-errors (in-game; OFF by default — enable with builder.WithRuntimeErrorCapture())

• runtime-errors-get — Read captured in-game runtime errors (oldest-first, newest-kept page); poll only new errors via sinceSequence. Returns available:false when capture was never enabled, so an empty list is never mistaken for health.
• runtime-errors-clear — Clear the captured in-game runtime-error buffer (a no-op when capture is not enabled); the monotonic sequence counter is preserved.

Requirements

• Godot 4.3+ — the C# / .NET (mono) edition. The addon csproj pins Godot.NET.Sdk/4.3.0 as its minimum floor; newer 4.x editors (4.4, 4.5) work.
• .NET 8 SDK (net8.0).

Installation

There are two things to install: the addon (the plugin files) and the two NuGet packages the addon's C# depends on. Godot compiles every .cs under your project into one assembly, so your project's .csproj must declare the same NuGet references the addon needs — otherwise the addon's C# will not compile.

Step 1: Add the addon

Pick one of the following ways to get the addons/godot_mcp/ folder into your Godot C# project.

Fully automated (recommended for terminal workflows): godot-cli install-plugin ./MyGodotProject does all of Step 1 and Step 2 in one command — it downloads addons/godot_mcp/ from the matching GitHub release, adds the two NuGet packages to your .csproj, and enables the plugin in project.godot, idempotently. Use --source <path>/addons/godot_mcp to install from a local copy offline. The manual Options A–C below remain for in-editor (Asset Library) and hand-managed installs.

Option A — Godot Asset Library (recommended)

The easiest path: install directly from inside the editor.

1. Open the AssetLib tab at the top of the Godot editor.
2. Search for Godot-MCP and open the asset.
3. Click Download, then Install — Godot unpacks the addon into your project's res://addons/godot_mcp/.

The Asset Library entry is published per release and always points at a tagged version, so an in-editor install gives you a known-good snapshot of the addon. (See note below if the entry is not visible yet.)

Option B — GitHub Release zip

Grab the latest godot-mcp-addon-<version>.zip from the Releases page and extract it into your project's root — the archive already contains addons/godot_mcp/..., so the files land at res://addons/godot_mcp/.

Option C — copy from source

Copy the addons/godot_mcp/ folder from this repository (or your clone) into your project's addons/ directory by hand.

---

After the files are in place (Options A–C), enable the plugin: Project → Project Settings → Plugins → Godot-MCP → Enable. (If you used the fully-automated godot-cli install-plugin above, the plugin is already enabled and the NuGet packages are already added — skip straight to Step 3.) On a successful load the editor Output panel prints:

[Godot-MCP] plugin loaded

Asset Library availability. The in-editor AssetLib entry (Option A) appears after the maintainer's first submission is approved by the Godot Asset Library moderators. Until then, use Option B (GitHub Release zip) or Option C.

Step 2: Add the NuGet packages

Add both PackageReferences to your project's .csproj (use these exact pinned versions — they must match the addon's Godot-MCP.csproj):

<ItemGroup>
  <PackageReference Include="com.IvanMurzak.ReflectorNet" Version="5.3.1" />
  <PackageReference Include="com.IvanMurzak.McpPlugin"   Version="6.10.0" />
</ItemGroup>

Package	Version	Role
com.IvanMurzak.ReflectorNet	5.3.1	Reflection / serialization core
com.IvanMurzak.McpPlugin	6.10.0	MCP plugin client (transitively pulls McpPlugin.Common + ReflectorNet; carries the shared AgentConfig module)

Run dotnet restore so the packages land in your NuGet cache, then build. No manual DLL copying is required — at editor runtime the addon's assembly resolver locates the DLLs in your NuGet global-packages folder by reading the build's *.deps.json. (If you prefer self-contained output, set <CopyLocalLockFileAssemblies>true</CopyLocalLockFileAssemblies> so the DLLs are copied beside your project assembly instead.)

Step 3: Install an AI agent

Choose a single AI agent you prefer — you don't need to install all of them. This is your main chat window to communicate with the LLM.

• Claude Code (recommended)
• Claude Desktop
• GitHub Copilot in VS Code
• Antigravity
• Cursor
• Any other MCP-aware agent

Write the agent's MCP-client config with godot-cli setup-mcp <agent> ./MyGodotProject — it points the client at the Godot server's <host>/mcp URL. See the CLI documentation for the full list of supported agents.

Connect

The plugin connects to an MCP server in one of two modes. The mode and its URL / token can be set in the serialized config or overridden at process start with environment variables (handy for CI, headless runs, and local dev). All variable names are the Godot analog of Unity-MCP's UNITY_MCP_*. The active mode always recomputes from the environment, so a process-level override wins over the serialized config without editing any file.

Cloud mode (default) — ai-game.dev

In Cloud mode the plugin connects to the hosted backend at https://ai-game.dev (the /mcp hub path is appended automatically). This is the default connectionMode.

Environment variable	Purpose	Default
GODOT_MCP_CONNECTION_MODE	Force the mode: Cloud or Custom (case-insensitive).	Cloud
GODOT_MCP_CLOUD_URL	Override the cloud base URL. A trailing /mcp is stripped if present; a non-http(s) value falls back to the default.	https://ai-game.dev
GODOT_MCP_TOKEN	Bearer token, routed to the active mode's token. Surrounding quotes are trimmed.	(none)

Custom mode — your own server

In Custom mode the plugin connects to a server URL you supply (a local dev server, a self-hosted instance, etc.).

Environment variable	Purpose	Default
GODOT_MCP_CONNECTION_MODE	Set to Custom to select this mode.	Cloud
GODOT_MCP_HOST	The custom server URL. Must be an absolute http(s) URL or it falls back to the default.	http://localhost:8080
GODOT_MCP_TOKEN	Bearer token (only needed if the server requires authorization).	(none)

Example — boot the editor pointed at a local server:

export GODOT_MCP_CONNECTION_MODE=Custom
export GODOT_MCP_HOST=http://localhost:5300
# export GODOT_MCP_TOKEN=...   # only if the server enforces auth

The godot-cli open command forwards these env vars for you via --mode, --url, --cloud-url, and --token flags.

Godot MCP Server setup

In Cloud mode you don't run a server at all — the plugin talks to ai-game.dev. If you want to host the server yourself (local dev, CI, or your own cloud), you have two options: let the addon download and run the matched server binary for you (recommended), or run it manually (advanced).

The server itself is the shared, engine-agnostic GameDev-MCP-Server — one server binary (gamedev-mcp-server) serving Unity-MCP, Godot-MCP, and Unreal-MCP. It is released from its own repo on its own version line; this addon pins the server version it consumes (the ServerVersion constant in addons/godot_mcp/Runtime/Connection/GodotMcpServerView.cs).

Local server — let the addon download & run it for you

In Custom mode the plugin can host its own MCP server — you don't have to build or launch anything by hand. Open the addon dock's Server card while Custom mode is selected and use the Local server row:

• Start Server — downloads the server build for the pinned server version, caches it, launches it, and the plugin connects to it. Stop Server terminates it (it is also stopped automatically when you close the editor).
• The download is the per-platform release asset gamedev-mcp-server-<rid>.zip — pulled over HTTPS from github.com only, from the GameDev-MCP-Server release tagged v<ServerVersion>, so the asset URL is: https://github.com/IvanMurzak/GameDev-MCP-Server/releases/download/v<ServerVersion>/gamedev-mcp-server-<rid>.zip. The <rid> (platform runtime identifier — e.g. win-x64, osx-arm64, linux-x64) is resolved automatically for your machine; all seven published RIDs are supported (win-x64/x86/arm64, linux-x64/arm64, osx-x64/arm64).
• The binary is cached under your project's .godot/mcp-server/<rid>/ folder (gitignored) and re-used on later launches; it is only re-downloaded when the pinned server version changes (an exact version match, so the editor plugin and the server it talks to never drift). The server is launched on the port from your Server URL (default http://localhost:8080), over the streamableHttp transport.

Version pinning & security. The download URL is derived solely from the addon's pinned ServerVersion constant and your platform RID — there is no arbitrary-URL binary execution. The addon version and the server version are decoupled: bumping the consumed server is an explicit addon change (a new ServerVersion), and the pinned v<ServerVersion> release must already exist on GameDev-MCP-Server before an addon release that pins it. If the release asset can't be fetched (you're offline), the addon logs a warning and the local server simply doesn't start — fall back to the manual run below, or use Cloud mode. The download is skipped entirely under CI (the CI / GITHUB_ACTIONS environment), where no local server is hosted.

This mirrors Unity-MCP's self-hosted server flow: the editor plugin manages the pinned server binary for you instead of requiring a manual build.

Run the server manually (advanced)

To run the server as a standalone / cloud process, download a GameDev-MCP-Server release binary (or use the aigamedeveloper/mcp-server Docker image). Both transports are supported: streamableHttp (HTTP) and stdio.

# HTTP transport on port 8080
./gamedev-mcp-server --client-transport streamableHttp --port 8080

# stdio transport — for local MCP clients that launch the server directly
./gamedev-mcp-server --client-transport stdio

Then point the plugin at it in Custom mode (GODOT_MCP_HOST=http://localhost:8080).

Choosing a transport: use stdio when the MCP client launches the server binary directly (local use — the most common setup); use streamableHttp when running the server as a standalone process or in the cloud and connecting over HTTP.

See the GameDev-MCP-Server README for the full argument / environment-variable table, the Docker image, and the cross-platform build matrix.

Customize Tools

Godot-MCP supports custom MCP Tool development directly in your project code. A tool family is a partial class decorated [AiToolType]; each tool method is decorated [AiTool("tool-name", …)] with a [Description] on the method and on each parameter to help the LLM understand it.

Any Godot API call (Node, Resource, EditorInterface, …) must run on the editor main thread — marshal it through MainThread.Instance.Run(...) (ReflectorNet's MainThread is backed by the Godot main-thread dispatcher on plugin boot). Never touch engine objects off-thread.

[AiToolType]
public partial class Tool_MyFeature
{
    [AiTool("my-custom-task", Title = "Do a custom task")]
    [Description("Explain to the LLM what this does and when to call it.")]
    public string CustomTask
    (
        [Description("Explain to the LLM what this parameter is.")]
        string inputData
    )
    {
        // ... work that does not touch the Godot API can run on this background thread ...

        return MainThread.Instance.Run(() =>
        {
            // ... touch EditorInterface / Node / Resource here, on the main thread ...
            return "[Success] Operation completed.";
        });
    }
}

Return a structured data model (ReflectorNet-serialized) or void for side-effect-only ops — never ad-hoc string formatting for parseable output. Use string? optional = null parameters (nullable + default) to mark them as optional for the LLM.

Runtime usage (in-game)

Everything above runs the MCP connection inside the Godot editor (the [Tool] EditorPlugin boots it for you). Godot-MCP can also run inside a running / exported game build (debug or release) — the Godot analog of Unity-MCP's runtime mode. This lets an LLM read and drive your live game state: imagine a Chess game whose bot logic you outsource to an LLM by exposing a couple of tools.

Two things make runtime mode different from editor mode, and both are deliberate:

• It never auto-connects. The editor plugin connects on boot; a game build does not. You write the opt-in code and decide when (if ever) to call Connect().
• There are no tools, prompts, or resources by default — strictly manual. The runtime ships zero MCP tools, prompts, and resources. You register every [AiToolType] tool, [AiPromptType] prompt, and [AiResourceType] resource yourself, in your own code — and each kind is independently optional (register prompts without any tools, or vice versa). (The addon's editor tool families are gated by #if TOOLS and don't even compile into a game build, so they can never leak in.)

The entry point is GodotMcpRuntime.Initialize(...) (namespace com.IvanMurzak.Godot.MCP.Runtime). Write it once — e.g. from a Godot autoload's _Ready() so a SceneTree exists:

using System.Reflection;
using com.IvanMurzak.Godot.MCP.Connection;   // GodotMcpConnectionMode, GodotMcpAuthOption
using com.IvanMurzak.Godot.MCP.Runtime;      // GodotMcpRuntime
using Godot;

public partial class GameMcp : Node
{
    private GodotMcpRuntimeHandle? _mcp;

    public override async void _Ready()
    {
        // 1) Build the connection (default OFF — nothing connects yet).
        _mcp = GodotMcpRuntime.Initialize(builder =>
        {
            builder.WithConfig(config =>
            {
                config.ConnectionMode = GodotMcpConnectionMode.Custom;   // your own server
                config.Host           = "http://localhost:8080";         // prefer loopback
                config.AuthOption     = GodotMcpAuthOption.Required;      // require a bearer token
                config.Token          = "your-secret-token";
            });

            // 2) Opt YOUR tools / prompts / resources in. Zero of each by default — this is the only way
            //    they get registered, and each kind is independently optional.
            builder.WithToolsFromAssembly(Assembly.GetExecutingAssembly());     // [AiToolType] classes
            builder.WithPromptsFromAssembly(Assembly.GetExecutingAssembly());   // [AiPromptType] classes
            builder.WithResourcesFromAssembly(Assembly.GetExecutingAssembly()); // [AiResourceType] classes
            //   …or register specific families:
            //   builder.WithTools(typeof(GameMcpTools));
            //   builder.WithPrompts(typeof(GameMcpPrompts));
            //   builder.WithResources(typeof(GameMcpResources));
        }).Build();

        // 3) Connect — explicit, the security-required opt-in. Retries in the background while
        //    KeepConnected is true (the default).
        await _mcp.Connect();
    }

    public override async void _ExitTree()
    {
        // 4) Disconnect on shutdown (or whenever you want to stop exposing tools).
        if (_mcp is not null)
            await _mcp.Disconnect();
    }
}

Builder surface (all fluent / chainable):

Call	What it does
GodotMcpRuntime.Initialize(configure)	Begin configuring; returns a GodotMcpRuntimeBuilder. configure may be null for the zero-tool, env-configured default.
builder.WithConfig(Action<GodotMcpConfig>)	Set Host / Token / ConnectionMode / AuthOption in code. Multiple calls compose in order.
builder.WithToolsFromAssembly(Assembly)	Register every [AiToolType] class in an assembly (usually Assembly.GetExecutingAssembly()).
builder.WithTools(params Type[])	Register specific [AiToolType] classes when a whole-assembly scan is too broad.
builder.WithPromptsFromAssembly(Assembly)	Register every [AiPromptType] class in an assembly. Independent of tools/resources.
builder.WithPrompts(params Type[])	Register specific [AiPromptType] classes.
builder.WithResourcesFromAssembly(Assembly)	Register every [AiResourceType] class in an assembly. Independent of tools/prompts.
builder.WithResources(params Type[])	Register specific [AiResourceType] classes.
builder.WithoutMainThreadDispatcher()	Skip the automatic main-thread-dispatcher bootstrap (only if you install your own autoload dispatcher).
builder.WithRuntimeErrorCapture()	Capture errors raised in the running game (GDScript runtime errors, push_error/push_warning, shader errors via the Godot 4.5+ engine hook; C# unhandled / unobserved-Task exceptions with full stack traces) and register the runtime-errors-* tool so an agent can poll them. OFF by default. See "Capturing in-game runtime errors" below.
builder.Build()	Finalize; returns a default-OFF GodotMcpRuntimeHandle.
handle.Connect() / handle.Disconnect()	Open / close the connection. handle.Dispose() tears it down on shutdown.

Initialize().Build() also guarantees a main-thread dispatcher Node in the running SceneTree (so tool handlers can marshal Godot API calls onto the engine main thread), unless you opt out with WithoutMainThreadDispatcher(). Call it once a SceneTree is live (e.g. from an autoload _Ready).

Capturing in-game runtime errors

In editor mode, console-get-logs and script-validate surface the plugin's own logs and GDScript parse errors. But errors raised inside a running game — a GDScript runtime error (a null dereference, a bad index), a push_error/push_warning, a shader error, or a C# unhandled exception — are not visible to an agent through those editor tools. Without this, an agent can launch the game, poll for logs, see silence, and wrongly conclude the game is healthy. This is the gap that blocks an unattended "keep fixing until no errors" loop for real gameplay/runtime bugs.

Opt in with WithRuntimeErrorCapture():

_mcp = GodotMcpRuntime.Initialize(builder =>
{
    builder.WithConfig(cfg => { /* host / token … */ });
    builder.WithRuntimeErrorCapture();   // capture in-game runtime errors + expose the runtime-errors-* tool
}).Build();

await _mcp.Connect();

That single call installs three best-effort capture channels and registers the runtime-errors-* tool:

1. Engine error stream (Godot 4.5+) — registers a Godot.Logger via OS.AddLogger, so GDScript runtime errors, push_error/push_warning, and shader errors raised in the running game are captured with their origin (file / line / function).
2. C# unhandled exceptions — AppDomain.CurrentDomain.UnhandledException, with the full managed stack trace.
3. C# unobserved Task exceptions — TaskScheduler.UnobservedTaskException, with the full managed stack trace. (It only observes for logging — it does not call SetObserved(), so your game's own escalation behavior is unchanged.)

An MCP client polls the captured errors with the runtime-errors-get tool (and clears the buffer with runtime-errors-clear):

Tool	What it returns / does
runtime-errors-get	A bounded, newest-kept list of { sequence, message, type, source, file, line, function, stackTrace, frames, timestamp }. Pass the previous result's highestSequence as sinceSequence to poll only new errors — the "did anything break since I last looked?" loop. Returns available:false when capture was never enabled (so an empty list is never mistaken for health).
runtime-errors-clear	Clears the captured buffer (the monotonic sequence counter is preserved, so a pre-clear sinceSequence poll still behaves).

Stack-trace fidelity (read this). The two error sources differ in depth:

• Engine errors (source: Engine) carry the error's origin — file:line and the originating function — plus the message and a type (Error / Warning / Script / Shader). On Godot 4.5+, a GDScript runtime error also carries the deep multi-frame call stack: frames is the ordered (innermost-first) backtrace — each { function, file, line } — and stackTrace is the engine's formatted rendering of it. On Godot < 4.5 (or a release build without call-stack tracking) frames is null and stackTrace is null (origin only). The frames are materialized off the engine's non-thread-safe ScriptBacktrace inside the logger callback on the originating thread — only plain managed values ever cross into the collector, never a live engine object.
• C# faults (source: UnhandledException / UnobservedTaskException) carry the full managed stack trace (inner exceptions inlined) in stackTrace, plus the CLR exception type name in type. (frames is null — the managed stack lives in the stackTrace string.)

Graceful degradation. On Godot < 4.5 there is no OS.AddLogger managed hook, so the engine channel is silently unavailable — the C# exception channels still work, and runtime-errors-get still functions (it just won't see GDScript runtime errors). And like the rest of runtime mode, capture is strictly opt-in — without WithRuntimeErrorCapture() nothing is hooked and there is no behavior change. Disposing the handle (handle.Dispose()) uninstalls the hooks.

⚠️ Security — information disclosure. Captured errors forward the full message and (for C# faults) the full managed stack trace to the connected agent through runtime-errors-get. Those strings can embed sensitive runtime data — absolute filesystem paths, machine/user names, query strings, or a secret/token that happened to appear in an exception message or argument. That is the intended diagnostic value, but it widens what is exposed over the connection. Enable WithRuntimeErrorCapture() only on a trusted connection: a loopback host (http://localhost:… / 127.0.0.1) with AuthOption = GodotMcpAuthOption.Required and a real token — never an unauthenticated public interface in a release build. See Security and docs/runtime-security.md.

Sample: a live game-state tool

A runtime tool is written exactly like an editor tool — a partial class decorated [AiToolType], each method decorated [AiTool("tool-name", …)] with a [Description] on the method and each parameter. Any Godot API call (Node, SceneTree, …) must run on the engine main thread — marshal it through MainThread.Instance.Run(...) (ReflectorNet's MainThread, backed by the dispatcher Initialize() bootstrapped for you).

This Godot analog of Unity-MCP's "Chess bot" sample exposes the live running SceneTree to the LLM — a pure-managed game-ping round-trip plus a game-scene-tree-summary that reads real Node state:

using System.ComponentModel;
using com.IvanMurzak.McpPlugin;              // [AiToolType], [AiTool]
using com.IvanMurzak.ReflectorNet.Utils;     // MainThread
using Godot;

[AiToolType]
public partial class GameMcpTools
{
    [AiTool("game-ping", Title = "Game Ping", ReadOnlyHint = true, IdempotentHint = true)]
    [Description("Runtime readiness probe. Echoes 'message' back, or returns 'pong-from-game' when omitted.")]
    public string GamePing(
        [Description("Optional message to echo back. When null/empty, returns 'pong-from-game'.")]
        string? message = null)
    {
        return string.IsNullOrEmpty(message) ? "pong-from-game" : message;
    }

    [AiTool("game-scene-tree-summary", Title = "Game Scene-Tree Summary", ReadOnlyHint = true)]
    [Description("Summary of the LIVE running game's SceneTree (current scene + root child node names).")]
    public SceneTreeSummary GameSceneTreeSummary()
    {
        // Touch the live SceneTree on the engine main thread — MainThread.Instance was installed by
        // GodotMcpRuntime.Initialize(...). Touching Node APIs off the main thread would fault.
        return MainThread.Instance.Run(() =>
        {
            var summary = new SceneTreeSummary();
            if (Engine.GetMainLoop() is not SceneTree tree || tree.Root == null)
            {
                summary.CurrentSceneName = "<no-scene-tree>";
                return summary;
            }

            summary.CurrentSceneName = tree.CurrentScene?.Name ?? "<none>";
            summary.RootChildCount   = tree.Root.GetChildCount();
            foreach (var child in tree.Root.GetChildren())
                summary.RootChildNames.Add(child.Name);
            return summary;
        });
    }
}

// Structured result (ReflectorNet-serialized — never ad-hoc string formatting for parseable output).
public sealed class SceneTreeSummary
{
    public string CurrentSceneName { get; set; } = string.Empty;
    public int RootChildCount { get; set; }
    public System.Collections.Generic.List<string> RootChildNames { get; set; } = new();
}

Register it from the Initialize(...) block above (WithToolsFromAssembly(Assembly.GetExecutingAssembly()) picks it up automatically), connect, and the LLM can now call game-ping / game-scene-tree-summary against your live game. Real example outsourcing bot logic: a chess-do-turn tool that calls into your game controller on the main thread, plus a chess-get-board tool returning a structured board model.

Same [AiToolType]/[AiTool]/MainThread.Instance.Run(...) contract as the editor Customize Tools section — the only difference is that in a game build you register the tools and you call Connect().

Sample: a prompt and a resource

Tools are not the only thing you can expose — MCP also has prompts (reusable instruction templates an LLM can request by name) and resources (addressable, read-only content the LLM can fetch by URI). They register exactly like tools: a partial class decorated [AiPromptType] / [AiResourceType], with each member decorated [AiPrompt(...)] / [AiResource(...)] and a [Description]. Register your prompt and resource classes the same way you register tools — WithPromptsFromAssembly(...) / WithResourcesFromAssembly(...) (or the by-type WithPrompts(...) / WithResources(...)) from the Initialize(...) block above. Each kind is independently optional — a game can expose prompts and/or resources with no tools at all.

using System.ComponentModel;
using com.IvanMurzak.McpPlugin;               // [AiPromptType], [AiPrompt], [AiResourceType], [AiResource]
using com.IvanMurzak.McpPlugin.Common.Model;  // Role, ResponseResourceContent
using com.IvanMurzak.ReflectorNet.Utils;      // MainThread
using Godot;

// A PROMPT — a named, reusable instruction the LLM can request. Returns the prompt text; Role marks who
// the message is from. Set Enabled = false to ship a prompt registered-but-off until you flip it on.
[AiPromptType]
public partial class GameMcpPrompts
{
    [AiPrompt(Name = "explain-game-state", Role = Role.User)]
    [Description("Ask the assistant to summarize the current game state for the player.")]
    public string ExplainGameState()
    {
        return "Read the live SceneTree via the game tools and explain the current game state in one paragraph.";
    }
}

// A RESOURCE — addressable read-only content fetched by URI. Route is the URI template; the method
// returns ResponseResourceContent[]. Any Godot API access marshals onto the main thread, exactly like a tool.
[AiResourceType]
public partial class GameMcpResources
{
    [AiResource(
        Name = "Live SceneTree node names",
        Route = "game://scene-tree/nodes",
        MimeType = "application/json",
        Description = "The root child node names of the live running game's SceneTree.")]
    public ResponseResourceContent[] SceneTreeNodes(string uri)
    {
        return MainThread.Instance.Run(() =>
        {
            var names = new System.Collections.Generic.List<string>();
            if (Engine.GetMainLoop() is SceneTree tree && tree.Root != null)
            {
                foreach (var child in tree.Root.GetChildren())
                    names.Add(child.Name);
            }

            var json = System.Text.Json.JsonSerializer.Serialize(names);
            return new[] { ResponseResourceContent.CreateText(uri, json, "application/json") };
        });
    }
}

Same independently-optional, manual-registration contract as tools. The [AiPrompt]/[AiResource] attribute names, Role enum, and ResponseResourceContent helper all come from the reused com.IvanMurzak.McpPlugin package the editor path already uses — nothing Godot-specific to learn.

Where the server URL and token come from

A game build never auto-loads the editor's saved config (that's an editor-only convenience). You supply host/token one of two ways — and they compose, with env winning over code at resolution time:

1. In code — builder.WithConfig(c => { c.Host = …; c.Token = …; }), as above.

2. Out-of-band — GODOT_MCP_* process environment variables or a project .env file (read live by GodotMcpConfig, so a build can be reconfigured without recompiling):

   Environment variable	Values	Description
   GODOT_MCP_CONNECTION_MODE	Cloud / Custom	Connection mode (a loopback host implies Custom).
   GODOT_MCP_CLOUD_URL	URL	Override the Cloud base URL (default https://ai-game.dev).
   GODOT_MCP_HOST	URL	Custom-mode server host (default http://localhost:8080).
   GODOT_MCP_AUTH_OPTION	None / Required	Whether Custom mode sends a bearer token.
   GODOT_MCP_TOKEN	string	The bearer token (routed to Cloud or Custom by the active mode).
   GODOT_MCP_LOG_LEVEL	Trace…None	Log-verbosity threshold.

   export GODOT_MCP_CONNECTION_MODE=Custom
   export GODOT_MCP_HOST=http://localhost:8080
   export GODOT_MCP_AUTH_OPTION=Required
   export GODOT_MCP_TOKEN=your-secret-token
   

• Cloud mode (GodotMcpConnectionMode.Cloud) connects to https://ai-game.dev (override with GODOT_MCP_CLOUD_URL).
• Custom mode (GodotMcpConnectionMode.Custom) connects to your own server — a local dev server, self-hosted, or a loopback address. This is the recommended mode for a shipped game (see below).

Security: opt-in only, default OFF

Exposing an MCP server inside a shipped game opens a remote-control surface: anything your registered tools can do, a connected MCP client can drive. Godot-MCP's runtime is built so this can only happen deliberately:

• Opt-in only / default OFF. Building a handle does not connect. Nothing happens until your code calls Connect(). There is no auto-connect path in a game build.
• Zero tools by default. A runtime with no WithTools… call registers nothing. The attack surface is exactly the set of tools you chose to register — no more.
• No persisted-config auto-load. A game build never silently reads a saved config file; host/token come only from your code or GODOT_MCP_* env / .env.
• Prefer loopback + a required token. For local tooling, bind to a loopback host (http://localhost:… / 127.0.0.1) and set AuthOption = GodotMcpAuthOption.Required with a real Token. Avoid exposing the connection on a public interface in a release build unless you have explicitly designed and secured that surface.
• Runtime-error capture forwards sensitive data. WithRuntimeErrorCapture() is OFF by default. When enabled, captured messages and stack traces are sent verbatim to the connected agent via runtime-errors-get and may contain absolute paths, machine/user names, or a secret that appeared in an exception — so enable it only on a trusted loopback + token connection (full note under Capturing in-game runtime errors).

Editor-side security notes (accepted posture)

The points above are about a game build. Two editor-side surfaces are documented here for completeness; both are by design today:

• Editor token storage is plaintext at rest. When you connect the editor plugin (Cloud device-auth or a Custom-mode token), the plugin persists your connection config — including the bearer token (token) and Cloud token (cloudToken) — as plaintext JSON in user://godot-mcp-config.json (resolved per Godot's user:// data directory). It is not encrypted or stored in an OS keystore. The trust assumption is the local user account: anyone with read access to your user data directory can read the token. Treat that file as a secret — don't commit it, sync it, or share it. To rotate, clear the saved token in the dock (or delete the file) and reconnect. (Process-env / .env overrides via GODOT_MCP_TOKEN always shadow the persisted value and are not written back to this file.)
• The dev-control bridge is unauthenticated but gated OFF. A development-only inject/control HTTP bridge exists for driving the editor dock in tests. It is unauthenticated, but its security boundary is threefold: it is editor-only (#if TOOLS, never compiled into a game), binds 127.0.0.1 only, and starts only when GODOT_MCP_DEV_CONTROL=1 — a shipped addon (and any editor session without the env var) never listens. That env gate is load-bearing and enforced by a unit test + a boot-time assertion, so it can never silently ship enabled.

A short standalone copy of this contract lives in docs/runtime-security.md.

How Godot MCP Architecture Works

Godot-MCP is a bridge between LLMs and the Godot editor. It exposes and explains Godot's tools to the LLM, which then understands the interface and uses the tools according to your requests.

On editor load, the [Tool] EditorPlugin (GodotMcpPlugin) boots the plugin: it installs a main-thread dispatcher, builds a ReflectorNet Reflector with Godot type converters, and opens a SignalR connection to an MCP server over the reused com.IvanMurzak.McpPlugin client. The AI tools it registers are then callable by any MCP-aware AI agent.

What is MCP

MCP — Model Context Protocol. In a few words, it is USB Type-C for AI, specifically for LLMs (Large Language Models). It teaches the LLM how to use external features — such as the Godot Engine in this case, or even your own custom C# method. Official documentation.

What is an AI agent

It is an application with a chat window. It may have smart agents to operate better, and embedded advanced MCP Tools. A well-built MCP client is 50% of the AI success in executing a task — which is why it is important to choose a good one.

What is the MCP Server

It is the bridge between the MCP Client and "something else" — in this case the Godot editor. In Cloud mode this is the hosted ai-game.dev backend; in Custom mode it is the shared GameDev-MCP-Server host you run yourself (or let the addon download and run for you).

What is an MCP Tool

An MCP Tool is a function the LLM can call to interact with Godot. These tools are the bridge between natural-language requests and actual Godot operations. When you ask the AI to "create a node" or "open a scene," it uses MCP Tools to execute the action. Tools have typed, described parameters; return structured results; and are thread-aware (main-thread for Godot API calls, background-thread for heavy processing).

Building & contributing

Godot.NET.Sdk is a NuGet SDK, so no Godot binary is required to compile or unit-test:

dotnet restore Godot-MCP.sln
dotnet build  Godot-MCP.sln --configuration Debug --no-restore   # 0 errors required (CI gate)
dotnet test   Godot-MCP.Tests/Godot-MCP.Tests.csproj --configuration Debug --no-build

A Godot 4.3+ editor is only needed for live behavioral verification of the engine-driving tools. See CLAUDE.md for the full build/test/run runbook, the editor-runtime assembly-load fix, conventions, and the headless testbed smoke.

Contributions are highly appreciated. Please give this project a star 🌟 if you find it useful!

1. 👉 Fork the project
2. Clone the fork and open it in a Godot 4.3+ (mono) editor
3. Implement new things, commit, and push to GitHub
4. Create a Pull Request targeting the original Godot-MCP repository, main branch.

License

Apache-2.0 © Ivan Murzak