MCP Server Part 7: get_dash_component tool and callback tool execution

[KoolADE85]

Summary

• Wires up the full tool pipeline following the same pattern as resources:

  • list_tools() builds the tool list from all registered tool providers
  • call_tool(name, args) routes LLM calls to the appropriate callback function

• Adds a static tool get_dash_component which allows LLMs to query a specific prop for a given ID.

Manual verification:

fromdashimportDash, html, dcc, Input, Outputimportjsonapp=Dash(__name__)
app.layout=html.Div([
dcc.Dropdown(id="city", options=["NYC", "LA"], value="NYC"),
dcc.Graph(id="chart"),
html.Div(id="summary"),
])
@app.callback(Output("chart", "figure"), Input("city", "value"))defupdate_chart(city):
return {"data": [], "layout": {"title": city}}
@app.callback(Output("summary", "children"), Input("city", "value"))defupdate_summary(city):
returnf"Showing data for {city}"withapp.server.app_context():
fromdash.mcp.primitives.toolsimportlist_tools, call_tool# List all tools — should include update_chart, update_summary, get_dash_componenttools=list_tools()
fortoolintools.tools:
print(f"- {tool.name}")
# Inspect a component — shows it's input to both callbacksresult=call_tool("get_dash_component", {"component_id": "city"})
print(json.dumps(json.loads(result.content[0].text), indent=2))
# "value" property should list both `update_chart` and `update_summary` in input_to_tool# Execute a callback via its toolresult=call_tool("update_summary", {"city": "LA"})
print(result.content[0].text) # Shows "Showing data for LA"

[github-actions]

Thank you for your contribution to Dash! 🎉

This PR is exempt from requiring a linked issue due to its labels.

[camdecoster]

I made a few suggestions. The one to pay attention to is the loop going through callbacks/inputs/outputs. Let me know what you think.

[camdecoster]

Suggested change

	value=callback_map.get_initial_value(f"{comp_id}.{prop_name}")
	id_and_prop=f"{comp_id}.{prop_name}"
	value=callback_map.get_initial_value(id_and_prop)

[camdecoster]

Suggested change

id_and_prop = f"{comp_id}.{prop_name}"

[camdecoster]

Suggested change

	raiseValueError("component_id is required")
	returnCallToolResult(
	content=[TextContent(type="text", text="component_id is required")],
	isError=True,
	)

[camdecoster]

Suggested change

	ifcomponentisNone:
	callback_map=get_app().mcp_callback_map
	callback_map=get_app().mcp_callback_map
	ifcomponentisNone:

[camdecoster]

Suggested change

callback_map = get_app().mcp_callback_map

[camdecoster]

This could get expensive for apps with a lot of callbacks, inputs, outputs. Is there a way to create and use an index for looking this up?

[KoolADE85]

Great point! The dash renderer actually implements such a mapping (but in JS obviously). I'll do the same on the python side.