MCP Server Part 2: Represent callback-related data with a CallbackAdapter

[KoolADE85]

Summary

• Add CallbackAdapter: wraps a Dash callback and exposes MCP-related metadata (computed lazily)
  • It combines Dash's own callback map, layout, and user docstrings/types into 1 interface that the MCP server will use to present a complete picture of the app to LLMs.
• Add CallbackAdapterCollection for working with collections of adapters
• Add mcp_enabled parameter to @app.callback() for opting callbacks out of MCP
• Add mcp>=1.0.0 to dependencies

Manual testing

• You can inspect what kind of data the CallbackAdapter exposes
• you can run callbacks directly with run_callback (which is what MCP will do)

from dash import Dash, html, dcc, Input, Output
from dash._get_app import app_context

app = Dash(__name__)
app.layout = html.Div([
    dcc.Input(id="name", value="World"),
    html.Div(id="greeting"),
])
@app.callback(Output("greeting", "children"), Input("name", "value"))
def greet(name):
    """Greet the user by name."""
    return f"Hello, {name}!"

with app.server.app_context():
    app_context.set(app)
    from dash.mcp.primitives.tools.callback_adapter_collection import CallbackAdapterCollection
    from dash.mcp.primitives.tools.callback_utils import run_callback
    collection = CallbackAdapterCollection(app)
    for adapter in collection:
        print(f"Tool: {adapter.tool_name}")
        print(f"  Docstring: {adapter._docstring}")
        print(f"  Outputs: {[o['id_and_prop'] for o in adapter.outputs]}")
        print(f"  Inputs:  {[i['name'] for i in adapter.inputs]}")

    # Execute the callback through the adapter
    adapter = collection[0]
    result = run_callback(adapter, {"name": "Alice"})
    print(f"Callback result: {result}")

[github-actions]

Thank you for your contribution to Dash! 🎉

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

[T4rk1n]

dash.mcp.types appears two times and there is a mix of absolute vs relative imports.

[T4rk1n]

Add a type to this return value.

[T4rk1n]

Add a type to this return value.

[T4rk1n]

I think returning the array and handling the results length at call site would be better since this makes the return value an union.

[T4rk1n]

Add type definition to the dict if possible.

[T4rk1n]

Could add a generic here [TInput, TOutput]

[T4rk1n]

What are these code? This one has the same code as the base MCPError