| Filename | Latest commit message | Latest commit date |
|---|---|---|
50eb30ec8d
The client, core and server packages become ^2.0.0 peers and client is now a required peer (App and AppBridge extend its Protocol class); server stays optional for View-only consumers. Examples move to zod ^4.2.0 to match the library peer range. The root package is not yet published at 2.0.0, so the lockfile now links the examples' @modelcontextprotocol/ext-apps dependency to the repository root instead of a registry copy. This drops the stale 1.x tarball (and its sdk 1.x peer) from the lockfile and makes scripts/link-self.mjs a no-op. |
||
| .. | ||
| src | ||
| .gitignore | ||
| index.html | ||
| package.json | ||
| README.md | ||
| sandbox.html | ||
| serve.ts | ||
| tsconfig.json | ||
| vite.config.ts | ||
Example: Basic Host
A reference implementation showing how to build an MCP host application that connects to MCP servers and renders tool UIs in a secure sandbox.
This basic host can also be used to test MCP Apps during local development.
Key Files
index.html/src/index.tsx- React UI host with tool selection, parameter input, and iframe managementsandbox.html/src/sandbox.ts- Outer iframe proxy with security validation and bidirectional message relaysrc/implementation.ts- Core logic: server connection, tool calling, and AppBridge setup
Getting Started
npm install
npm run start
# Open http://localhost:8080
By default, the host application will try to connect to an MCP server at http://localhost:3001/mcp. You can configure this behavior by setting the SERVERS environment variable with a JSON array of server URLs:
SERVERS='["http://localhost:1234/mcp", "http://localhost:5678/mcp"]' npm run start
Architecture
This example uses a double-iframe sandbox pattern for secure UI isolation:
Host (port 8080)
└── Outer iframe (port 8081) - sandbox proxy
└── Inner iframe (srcdoc) - untrusted tool UI
Why two iframes?
- The outer iframe runs on a separate origin (port 8081) preventing direct access to the host
- The inner iframe receives HTML via
srcdocand is restricted by sandbox attributes - Messages flow through the outer iframe which validates and relays them bidirectionally
This architecture ensures that even if tool UI code is malicious, it cannot access the host application's DOM, cookies, or JavaScript context.