QML SceneGraph MCP Bridge

A MCP server that bridges GammaRay probe introspection data into MCP tools, enabling LLMs to inspect and debug Qt Quick / QML scene graphs, items, geometry, and materials.

Architecture

Target Qt/QML App  ──TCP──►  GammaRay MCP Bridge  ──stdio──►  LLM / AI Agent
  (GammaRay probe                (GammaRay client +               (opencode,
   injected)                      qtmcp MCP server)                Claude Desktop, etc.)

The bridge is a GammaRay client: it connects to a probe injected into a target Qt/QML app, reads the same models the GammaRay GUI uses, and translates them into MCP JSON-RPC tool calls over stdio.

Prerequisites

Qt 6.8+ (system)
C++20 compiler (GCC 12+, Clang 16+)
GammaRay 3.4.0+ built from source (see build instructions)
qtmcp (consumed via FetchContent — no manual install)
Python 3.10+ with pytest (for running the test suite)

Building

1. Build and install GammaRay

cmake -S /path/to/GammaRay -B /path/to/GammaRay/build \
  -DCMAKE_INSTALL_PREFIX=$(pwd)/install-prefix
cmake --build /path/to/GammaRay/build
cmake --install /path/to/GammaRay/build --prefix $(pwd)/install-prefix

2. Build the bridge

cd bridge
cmake -S . -B build -G Ninja -DCMAKE_PREFIX_PATH=$(pwd)/../install-prefix
cmake --build build

3. Run

# Start a probe (inject into a QML app)
install-prefix/bin/gammaray --inject-only --listen tcp://127.0.0.1:11732 \
  --injector preload /usr/lib/qt6/bin/qml /path/to/app.qml -platform offscreen

# Start the bridge (stdio MCP server)
bridge/run.sh

The bridge starts in lazy-connect mode. Call connectProbe("127.0.0.1", 11732) from your MCP client once the probe is up.

MCP Tools

Connection management

Tool	Description
`connectProbe(host, port)`	Connect to a GammaRay probe (defaults: 127.0.0.1:11732)
`connectProbeDefault()`	Convenience: connect to 127.0.0.1:11732
`disconnectProbe()`	Drop connection and forget URL
`probeStatus()`	Report connection state

Tool	Description
`listQuickWindows()`	List QQuickWindows in the target app
`selectQuickWindow(index)`	Select a window for scene graph introspection
`listQuickItems()`	Recursive QQuickItem tree with types and flags
`listScenegraphNodes()`	Recursive QSGNode tree (all node types)

QML Item inspection

Tool	Description
`selectQuickItem(address)`	Select a QML item by address, populating its properties model
`getItemProperties(address)`	Get all Q_PROPERTY values (x, y, width, height, opacity, visible, z, anchors, text, font, etc.)

SG Node inspection

Tool	Description
`selectScenegraphNode(address)`	Select a SG node, populating geometry/material sub-models
`getNodeVertices(address)`	Read vertex data of a GeometryNode
`getNodeAdjacency(address)`	Read adjacency/drawing mode of a GeometryNode
`getMaterialShaders(address)`	List shader stages for a node's material
`getShaderSource(row)`	Get shader source code (async via MaterialExtensionInterface)
`getMaterialProperties(address)`	Get material property name/value pairs

Rendering visualization

Tool	Description
`setRenderMode(mode)`	Set render mode (NormalRendering, VisualizeOverdraw, etc.)
`setSlowMode(enabled)`	Toggle continuous rendering

Testing

# Unit tests only (no probe needed):
./tests/run_tests.sh --no-probe

# Full integration test suite (probe required):
./tests/run_tests.sh --no-probe  # skips probe-dependent tests
./tests/run_tests.sh -v          # verbose

See tests/README.md for details.

License

GPL-2.0-or-later. The bridge links GammaRay libraries (GPL-2.0-or-later) and uses qtmcp (available under GPL-2.0-only).

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