rbx-mcp-hub

Free, MIT-licensed multi-place MCP hub for Roblox Studio. Route Claude Code, Cursor, Codex, or any other MCP-speaking AI agent to the correct Studio window by PlaceId so you can work on multiple Roblox games at the same time, one agent session per game, with no command-queue races.

Why this exists

Roblox's official MCP servers — the (now archived) studio-rust-mcp-server and the built-in Studio MCP server — share a single command queue across every open Studio window. The built-in server does expose list_roblox_studios + set_active_studio tools, but they require the agent to explicitly "switch" Studios per tool call; you also hit races when two agents send commands concurrently.

rbx-mcp-hub solves this by adding PlaceId-based routing on top of the same HTTP protocol:

• One hub daemon binds 127.0.0.1:44755 (singleton).
• One MCP bridge per Claude project; .mcp.json stamps its RBX_PLACE_ID onto every outbound tool call.
• One Studio plugin per open place; registers with context = tostring(game.PlaceId) on load.

The hub matches by context. Every Claude session is permanently wired to its game's PlaceId — no per-call switching, no races.

Works with any MCP client

The bridge is a plain stdio MCP server — any client that supports stdio MCP can use it. That includes Claude Code, Cursor, Codex, Cline, and Continue. rbx-mcp-hub init writes a Claude-Code-flavored .mcp.json; for other clients, point your client's MCP config at node <repo>/src/bridge.js with RBX_PLACE_ID (and optionally RBX_PLACE_NAME) in the env.

Architecture

┌───────────────────┐   stdio MCP   ┌──────────────┐
│  Claude Code      │──────────────▶│  MCP Bridge  │
│  (project A)      │               │  (per-proj)  │
└───────────────────┘               └──────┬───────┘
┌───────────────────┐   stdio MCP   ┌──────▼───────┐
│  Claude Code      │──────────────▶│  MCP Bridge  │
│  (project B)      │               │  (per-proj)  │
└───────────────────┘               └──────┬───────┘
                                            │ HTTP (context=PlaceId)
                                            ▼
                                    ┌────────────────┐
                                    │   Hub Daemon   │ :44755
                                    │   (singleton)  │
                                    └───┬──────┬─────┘
                                        │ long-poll per-context
                          ┌─────────────┘      └─────────────┐
                          ▼                                  ▼
                ┌────────────────┐                 ┌────────────────┐
                │ Studio Plugin  │                 │ Studio Plugin  │
                │ PlaceId: 1234  │                 │ PlaceId: 5678  │
                └────────────────┘                 └────────────────┘

Prerequisites

• Node.js 18 or newer (node -v)
• Git
• Roblox Studio

No Rust or Rojo toolchain required. The Studio plugin ships prebuilt in the repo.

First-time install

# 1. Install from npm
npm install -g rbx-mcp-hub

# 2. Copy the Studio plugin .rbxm into Roblox's Plugins folder
rbx-mcp-hub install-plugin

# 3. Start the hub daemon (runs in background)
rbx-mcp-hub start

Prefer source? git clone https://github.com/Blankscarface23/rbx-mcp-hub.git && cd rbx-mcp-hub && npm install && npm link and continue from step 2.

Keep the hub running — it's a long-lived singleton. Re-run rbx-mcp-hub start after reboots, or wire it into your OS's startup manager.

Migrating from studio-rust-mcp-server

If you previously installed the archived Roblox/studio-rust-mcp-server, its MCP server entry stays registered in your Claude Code config even after you switch to rbx-mcp-hub. Because you now have the rbx-mcp-hub Studio plugin installed (not the old server's companion plugin), the stale entry has no plugin to talk to and every tool call fails with:

error decoding response body

That phrase is the Rust reqwest library reporting it got an HTTP response it couldn't decode — in practice it means the old server's internal long-poll never received a plugin response. Clean it up:

1. Find the stale entry. In each project where you used the old server:

   claude mcp list

   Look for an entry named Roblox_Studio (or similar) pointing at something like rbx-studio-mcp.exe or studio-rust-mcp-server.

2. Check its scope, then remove it. The archived installer typically registers per-project (local scope):

   claude mcp get Roblox_Studio          # shows Scope: Local or User
   claude mcp remove "Roblox_Studio" -s local

   Use -s user instead if the scope is User. Repeat for every project that lists it.

3. Delete the old plugin .rbxm from your Roblox plugins folder if it's still there — otherwise it'll fight for the same port the next time you launch Studio:

   • Windows: %LOCALAPPDATA%\Roblox\Plugins\
   • macOS / Linux: ~/Documents/Roblox/Plugins/

   Common filenames: MCPStudioPlugin.rbxm, studio-rust-mcp-server.rbxm.

4. If your project's .claude/settings.local.json has permission grants like mcp__Roblox_Studio__run_code, rename the prefix to mcp__rbx-mcp-hub__ so Claude doesn't re-prompt after the switch.

5. (Optional) Delete the old binary itself (e.g. ~/Downloads/rbx-studio-mcp.exe) — it's no longer needed.

Then continue with Per-project setup. After you restart each Claude Code session, claude mcp list from the project should show only rbx-mcp-hub for Studio tooling.

Per-project setup

From inside each Roblox game project directory:

rbx-mcp-hub init

You'll be prompted for the game's PlaceId. Use the number from the Creator Dashboard URL, or run print(game.PlaceId) in Studio's command bar. For unpublished drafts, enter 0.

The command writes a .mcp.json that points at the bridge and sets RBX_PLACE_ID. Open the place in Studio, then open Claude Code in the project folder — Claude will prompt to authorize the MCP server; accept.

Verify it's working

1. In each Studio window, look at the Output tab. You should see:

   [rbx-mcp-hub] 🔌 v0.1.0 · PlaceId=<id> · Name=<place> · hub 127.0.0.1:44755
   [rbx-mcp-hub] 🟢 connected

   The toolbar button is highlighted when connected. Click it to pause or resume the connection.

2. Run rbx-mcp-hub status — every Studio should appear:

   hub on 127.0.0.1:44755
     ✓ placeId=1234 name=MyGame queue=0 lastSeen=2s ago
     ✓ placeId=5678 name=OtherGame queue=0 lastSeen=1s ago

3. In Claude Code, call get_studio_mode from the rbx-mcp-hub MCP server. A response that matches the right place confirms end-to-end routing.

Troubleshooting

| Symptom | Likely cause | Fix | | --- | --- | --- | | hub unreachable at 127.0.0.1:44755 in Claude Code | Hub daemon not running | rbx-mcp-hub start | | no active plugin for context=<id> | Studio isn't open on that place, plugin disabled, or RBX_PLACE_ID in .mcp.json doesn't match game.PlaceId | Open the correct place; enable rbx-mcp-hub in Plugins → Manage Plugins; double-check .mcp.json | | error decoding response body on every tool call | Stale MCP registration from the archived studio-rust-mcp-server — its companion Studio plugin is no longer installed | See Migrating from studio-rust-mcp-server | | 🔴 disconnected · ConnectionRefused in Studio Output | Hub crashed or not started | rbx-mcp-hub status, restart if needed | | Two Studios both route to each other | Both places have PlaceId = 0 (unpublished) | Only run one unpublished place at a time, or publish both | | Tool call goes to the wrong Studio anyway | Stale RBX_PLACE_ID (you published after init) | Edit .mcp.json with the real PlaceId and restart Claude Code; the plugin auto-re-registers when game.PlaceId changes |

Alternatives

| Tool | Price | Multi-place | Notes | | --- | --- | --- | --- | | rbx-mcp-hub (this) | Free, MIT | ✅ per-project auto-routing by PlaceId | Narrow tool; no bulk ops | | Roblox built-in Studio MCP | Free, ships with Studio | ⚠️ via manual set_active_studio per call | Recommended for single-user workflows | | Roblox/studio-rust-mcp-server | Free, MIT, archived | ❌ single queue | Superseded by the built-in | | boshyxd/robloxstudio-mcp | Free, MIT | ❌ single queue | Broad tool surface (50+ tools) | | hope1026/weppy-roblox-mcp | Free tier + paid Pro | ✅ (Pro only) | Bundles multi-place with terrain, audio, bidirectional sync, etc. |

Pick rbx-mcp-hub if you want a free, minimal, zero-config-per-call way to run multiple Claude sessions against multiple Studios. Pick the built-in if you're a single user juggling two Studios and don't mind per-call switching. Pick WEPPY Pro if you want the full feature bundle.

Rebuilding the plugin (contributors only)

Plugin source is under plugin/src/. Studio's built-in Script Sync works fine for iterating: open a blank place, enable Script Sync against plugin/src/, then use Save as Local Plugin to rebuild the .rbxm. Rojo also works (rojo build plugin/default.project.json -o plugin/build/rbx-mcp-hub.rbxm) but isn't required for end users.

Wire protocol

Same HTTP endpoint shape as the Rust server, plus a context query parameter for routing:

| Endpoint | Method | Purpose | | --- | --- | --- | | /request?context=<placeId> | GET | Plugin long-polls for commands targeted at this PlaceId (up to 15 s). | | /response | POST | Plugin returns a tool result (body {id, result, error}). | | /proxy | POST | Bridge submits a tool call (body {id, context, tool, params}). Blocks until the plugin responds. | | /status | GET | List connected plugins. |

JSON field names differ from the archived Rust server's ({id, tool, params} vs {id, args:{<tool>:{...}}}), so the plugins are not cross-compatible. Commands carry a UUID so multiple in-flight calls can't mix up responses.

Tools (v0.1.3)

• run_code — execute arbitrary Luau in the Edit DataModel. Returns tagged output ([OUTPUT], [WARNING], [RETURNED RESULTS], [COMPILE ERROR], [UNEXPECTED ERROR]). Deep-serializes complex return values (userdata like CFrame/Vector3/Instance, cyclic tables, mixed-key tables) via clone + stringify. Captures multi-value returns (return a, b, c).
• insert_model — accepts either query (free-form marketplace search via InsertService:GetFreeModels; top match inserted) or assetId (direct). Collapses loaded objects into a Model/Folder. Model roots are pivoted to the point under the Studio camera's viewport center, so inserts land where you're looking.
• get_console_output — read recent LogService lines.
• get_studio_mode — report Edit / Play / Run / Stopped.
• start_stop_play — enter Play or Run mode, or stop the current session. Backed by StudioTestService:ExecutePlayModeAsync / ExecuteRunModeAsync; Stop uses a cross-DataModel signal watched by the plugin running in the play-mode Server DataModel.
• run_script_in_play_mode — one-shot test runner. Injects a wrapper Script into ServerScriptService, enters Play or Run mode (via mode: "play" | "run"), pcalls your code on the play-mode Server, captures return value + LogService output, calls StudioTestService:EndTest to stop, and returns the result. Times out after timeoutSeconds (default 10).

All mutating tool calls are wrapped in ChangeHistoryService:TryBeginRecording("rbx-mcp-hub:<tool>") so Ctrl+Z in Studio cleanly reverses whatever an MCP client just did.

Later versions will expand toward a 15+ tool surface (tree, get, editScript, etc.) and client-side run_script_in_play_mode.

Security

• Hub binds 127.0.0.1 only. Never exposed to LAN.
• run_code executes arbitrary Luau with plugin-level privileges. Only use with MCP clients you trust.
• No authentication across localhost. Other processes on your machine can already read your files, so the threat model is local.

Support

If this saves you time juggling multiple Studios, consider sponsoring development on GitHub Sponsors. The project stays free and MIT either way — sponsorship just helps keep the roadmap moving.

License

MIT. Derived in part from Roblox/studio-rust-mcp-server (MIT) — specifically the HTTP endpoint paths and the initial tool list. Plugin and multi-place routing are original work.