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[BUG] MCP errors in get_dash_component tool #4113
Description
When the get_dash_component MCP tool queries a container whose children contains Dash components, an error is raised:
MCP error: Unable to serialize unknown type: <class 'dash.html.H1.H1'>
Traceback (most recent call last):
File "/home/aborrmann/projects/dash/dash/mcp/_server.py", line 337, in _dispatch_mcp_message
result=result.model_dump(exclude_none=True, mode="json"),
~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/aborrmann/projects/dash-user/.venv-editable/lib64/python3.14/site-packages/pydantic/main.py", line 475, in model_dump
return self.__pydantic_serializer__.to_python(
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
self,
^^^^^
...<13 lines>...
polymorphic_serialization=polymorphic_serialization,
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
)
^
pydantic_core._pydantic_core.PydanticSerializationError: Unable to serialize unknown type: <class 'dash.html.H1.H1'>
Activity
fix(mcp): serialize Dash component values before emitting tool result (…
test(mcp): cover nested Dash children in JSON-RPC tool output (plotly…