sbox-mcp-plus

Extensions to the s&box editor's built-in MCP server. The editor already runs an MCP server on http://127.0.0.1:7269/mcp and discovers tools from library code live — this library adds tools the stock set is missing, so agents get them today instead of waiting on engine releases.

All tool names are prefixed x_ so they can never collide with the engine's own once the upstream equivalents land.

Install

Drop this library into your project's Libraries/ folder (or install it as a package once published). Libraries are scanned at project load — restart the editor after first install; after that, edits to the code hotload.

Find the tools from any MCP client via list_toolsets (toolset extras) or search_tools.

Tools

x_open_scene

Make a scene the active editor tab, opening it from its asset path if it isn't open yet. Accepts a scene name or resource path as list_scenes reports them.

Why it exists: the stock toolset can read and list background scenes but can't switch which one is active, and every mutating tool (set_component, save_scene, undo) targets the active scene. Worse, an edit aimed at a background scene mutates the object but the dirty flag lands on the active tab — the background scene reloads from disk on focus and the edit is silently lost. Upstream: issue #11637, PR #11638 (open).

• Explicit no-op message when the scene is already the active tab.
• Refuses during play mode — play_stop first.
• Refuses the running game session (it has no tab to switch to).

x_editor_status

What the editor is doing right now, from the editor's point of view: active scene tab name and path, unsaved-changes flag, open tab count, project ident, play/pause state.

Why it exists: the built-in editor_status reports the game scene handle, not the active editor tab — while editing it returns a placeholder name ("Scene") and a null path, and its dirty flag can describe a different scene than its name. Upstream: issue #11639, PR #11640 (closed unmerged). x_editor_status reads SceneEditorSession.Active — the same source list_scenes uses — so the two always agree.

Fields the built-in reports that this tool deliberately omits (tool count, compile status, engine paths): they come from engine-internal API a library can't reach, and the built-in editor_status still reports them correctly — use both.

x_camera_screenshot

Render a scene camera to an image with UI text intact. Same arguments as the built-in camera_screenshot — camera (a CameraComponent id, its game object's id, or empty for the scene's main camera), width, height, includeUi — so it's a drop-in swap.

Why it exists: the built-in camera_screenshot renders every Razor text label as a flat gray rectangle at any size other than the live viewport's. Upstream: issue #11585. Engine root cause: CameraComponent.ResizeUI relayouts each screen panel for the offscreen size but omits RootPanel.BuildDescriptors(), so labels resized by that relayout release their text texture while the render descriptors still point at the dead one — ScreenshotService has the correct sequence (PreLayout/CalculateLayout/PostLayout/BuildDescriptors).

In play mode x_camera_screenshot sidesteps it by capturing at exactly the current screen size, where the relayout changes no panel's size and no texture is released, then downscaling the capture to the requested dimensions. In edit mode there is no game viewport, so no live screen-size UI exists whose text textures a relayout could destroy, and it renders directly at the requested size — full detail, no resize step. Either way it works wherever camera_screenshot does.

Known issues

• The built-in editor_status is still broken while this library only routes around it — a library can't patch engine-assembly tools. Until upstream fixes it, trust x_editor_status or list_scenes.IsActive, not editor_status's scene fields.
• Tool errors arrive with a full .NET stack trace appended after the message. That's the engine MCP server's error formatting (its own tools do the same); the first line is the actionable part.
• x_open_scene can't target a never-saved scene by path (it has no resource path yet) — use its name.
• x_camera_screenshot output detail is capped at the live viewport's resolution in play mode: it captures there and resizes, so a requested size larger than the viewport is interpolation, not extra detail. Aspect ratio still follows the requested size. Edit mode renders at the requested size directly and isn't capped.
• Adding this library to a project doesn't take effect in an already-running editor: package mounting happens at project load, only source edits hotload. Restart once.