Host matrix

Run mountly-mcp dev while you iterate. Ship the same dist/ artifacts to a real host over the transport you choose.

Local preview

pnpm dev   # scaffold: mountly-mcp dev --server ./server.mjs

You exercise handshake, CSP, tool results, and View-initiated tool calls. Open the App once in Claude or VS Code before you call it done.

Host status

Host	Status	Connect
mountly-mcp dev	Supported	Built-in AppBridge + sandbox proxy
Claude Desktop	Supported (stdio)	claude_desktop_config.json → node + serve-stdio.mjs
VS Code MCP	Supported (stdio)	.vscode/mcp.json → same stdio entry
ChatGPT	Supported (HTTP)	Developer mode connector → HTTPS /mcp; OpenAI extensions via @openai/mcp-extensions
Other SEP-1865 hosts	Untested here	Same manifest if the host implements ui://

“Untested” means this repo has no CI against that host. Do not assume coverage.

Stdio entry

Scaffolds ship serve-stdio.mjs:

import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
import createServer from "./server.mjs";

const server = await createServer();
await server.connect(new StdioServerTransport());

Log to stderr. stdout is the JSON-RPC channel.

Claude Desktop

~/Library/Application Support/Claude/claude_desktop_config.json (macOS):

{
  "mcpServers": {
    "my-app": {
      "command": "node",
      "args": ["/absolute/path/to/serve-stdio.mjs"]
    }
  }
}

VS Code

.vscode/mcp.json:

{
  "servers": {
    "my-app": {
      "type": "stdio",
      "command": "node",
      "args": ["${workspaceFolder}/serve-stdio.mjs"]
    }
  }
}

ChatGPT

Serve Streamable HTTP (typically /mcp) over HTTPS. Tunnel locally or deploy.

1. pnpm add @openai/mcp-extensions
2. Pass openaiUi on the View and openaiUiToolMeta({ entrypoints: [...] }) on tools via mountly-mcp/openai/server
3. In the View, import { useOpenAIExtensions } from "mountly-mcp/react/openai"
4. ChatGPT → Settings → Security and login → Developer mode
5. Plugins → + → paste https://…/mcp → Create
6. New chat, enable the connector, prompt a tool, or open a global entrypoint from Desktop sidebar

Mountly leaves OAuth and hosting to you. Refresh the connector after metadata changes.

ChatGPT-only surfaces

Plugin Extensions place the same View on extra ChatGPT surfaces via tool openai/ui entrypoints. Every other host ignores them and renders the View inline.

Entrypoint type	Surface
global	Sidebar panel (+ quickAction)
thread	Conversation panel
file	File viewer/editor by extensions
settings	Plugin settings

MCP Events let your server notify ChatGPT through webhooks. They need an MCP 2.0 server (2026-07-28). mountly-mcp/events implements the draft spec; the package README shows the wiring.

Before host smoke

npx mountly-mcp build
npx mountly-mcp verify --strict --render

--render fails blank Views in Chromium. Host screenshots stay manual until each vendor exposes stable automation.

Text-only hosts

Hosts without MCP Apps still get tool text: Mountly adds a JSON text block when your handler returns only structuredContent. How it works.