| Filename | Latest commit message | Latest commit date |
|---|---|---|
741b1d3925* refactor(basic-host): use SDK types for ModelContext and AppMessage - Import McpUiUpdateModelContextRequest and McpUiMessageRequest from SDK - Replace custom ModelContext with McpUiUpdateModelContextRequest['params'] - Replace custom AppMessage with McpUiMessageRequest['params'] - Pass full message params instead of extracting text - Format messages by extracting text from content blocks in display * feat(basic-host): handle non-text content blocks in display - Add formatContentBlock helper for text, image, audio, resource types - Show placeholders like <image: image/png> for non-text content - Apply to both messages and model context display * test: update shadertoy screenshot * test: update screenshots from CI (linux x64) |
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| .. | ||
| src | ||
| 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.