A comprehensive testing/debugging tool for the MCP Apps SDK that exercises every capability, callback, and result format combination.
Configurable tool for testing all result variations:
| Parameter | Type | Default | Description |
|---|---|---|---|
contentType |
"text" | "image" | "audio" | "resource" | "resourceLink" | "mixed" |
"text" |
Content block type to return |
multipleBlocks |
boolean | false |
Return 3 content blocks |
includeStructuredContent |
boolean | true |
Include structuredContent in result |
includeMeta |
boolean | false |
Include _meta in result |
largeInput |
string | - | Large text input (tests tool-input-partial) |
simulateError |
boolean | false |
Return isError: true |
delayMs |
number | - | Delay before response (ms) |
App-only tool (hidden from model) for polling server state. Returns current timestamp and call counter.
The debug app provides a dashboard with:
- Event Log: Real-time log of all SDK events with filtering
- Host Info: Context, capabilities, container dimensions, styles
- Callback Status: Table of all callbacks with call counts
- Actions: Buttons to test every SDK method:
- Send messages (text/image)
- Logging (debug/info/warning/error)
- Model context updates
- Display mode requests
- Link opening
- Resize controls
- Server tool calls
- File operations
# Build
npm run --workspace examples/debug-server build
# Run standalone
npm run --workspace examples/debug-server serve
# Run with all examples
npm startThen open http://localhost:8080/basic-host/ and select "Debug MCP App Server" from the dropdown.