How it works
Inspect the complete boundary.
A tool can be valid MCP but still fail to render when its resource URI is absent, misspelled or served with the wrong content type. MCP App HTML uses text/html;profile=mcp-app and content supplies exactly one text or blob payload.
Use nested _meta.ui.resourceUri, verify exact URI equality and include only model or app in visibility. Keep a useful text result so unsupported hosts still provide a functional fallback.
Continue debugging
- Run the browser validator.
- Review sandbox CSP metadata.
- Resolve resource and metadata errors.
- Finish with the official conformance tooling and a supported MCP host.
MCP App Ready is independent and is not affiliated with the Model Context Protocol project.