3dstreet MCP server

3dstreet-mcp

A [Model Context Protocol][mcp] relay that lets [Claude Desktop][cd] or [Claude Code][cc] drive a [3DStreet][3ds] scene running in your browser.

Is this the right tool? This relay is the fallback for MCP clients

that cannot use WebMCP. If your agent runs inside a browser (ChatGPT's

desktop browser, Gemini in Chrome, Chrome 149+ with the WebMCP origin

trial or chrome://flags/#enable-webmcp-testing), you do not need this

package: open and the page registers the same

tools with the browser via document.modelContext — nothing to install,

no pairing. See the [3DStreet WebMCP docs][webmcp]. Use this relay only

for clients with no browser of their own or no WebMCP support (Claude

Desktop, Claude Code, Cursor, headless scripts). It will be retired once

those clients read WebMCP natively.

Listed on the [MCP Registry][registry] as app.3dstreet/3dstreet.

Status: alpha — protocol may change. Tracks [3DStreet#1582][issue] (design) and [3DStreet#1600][pr] (browser side). Scene creation works in any 3dstreet.app tab; saving and geospatial features require a free 3DStreet account.

How it works

Claude Desktop  ── stdio MCP ──▶  3dstreet-mcp  ── ws://127.0.0.1:51735 ──▶  3DStreet tab
or Claude Code                    (this package)                              (your browser)

The relay speaks MCP over stdio and bridges every tools/list and tools/call to a 3DStreet tab over a localhost WebSocket. The tab does the actual work — it's already signed in, has the catalog loaded, owns the cloud-save flow. The relay is a dumb pipe.

No auth tokens cross the WebSocket. The relay's port binds to 127.0.0.1 only and rejects WebSocket upgrades from origins outside the 3DStreet allowlist (https://3dstreet.app, https://dev-3dstreet.web.app, http://localhost:3333, http://127.0.0.1:3333).

Setup

Claude Desktop

Edit ~/Library/Application Support/Claude/claudedesktopconfig.json (macOS) or %APPDATA%/Claude/claudedesktopconfig.json (Windows):

{
  "mcpServers": {
    "3dstreet": {
      "command": "npx",
      "args": ["-y", "3dstreet-mcp"]
    }
  }
}

Restart Claude Desktop.

Claude Code

claude mcp add 3dstreet -- npx -y 3dstreet-mcp

Pair the browser tab

On startup the relay prints an auto-pair URL to its log, like:

open this URL to pair a 3DStreet tab: https://3dstreet.app/#mcp

Open that URL in a signed-in browser and the editor will detect the #mcp fragment, open the AI Assistant pane, and pair with the relay automatically — no console commands needed. (If you ran the relay on a non-default port the URL will look like https://3dstreet.app/#mcp=PORT.)

If you'd rather pair manually: open , click AI Assistant in the right panel, type /mcp, and click Reconnect.

You can now ask Claude things like:

• "What's in my current scene?"
• "Add a bike lane on the left side of the street."
• "Change the environment preset to night."

Toggle Read-only in the status bar to block scene mutations (useful when you just want Claude to explain a scene).

CLI

3dstreet-mcp [options]

Options:
  -p, --port <number>    WebSocket port (default 51735)
  -o, --origin <url>     Origin used in the printed auto-pair URL and
                         the MCP `instructions` hint (default
                         https://3dstreet.app — set to
                         http://localhost:3333 when running 3DStreet
                         from a local dev server)
  -h, --help             Show this help
  -v, --version          Print version and exit

If you need a different port (e.g. running two Claude clients against two different tabs), pass --port and open the auto-pair URL the relay prints — https://3dstreet.app/#mcp=PORT — which both selects the port and triggers auto-pair.

Shortened. The full README is on GitHub.