MCP Server Part 8: MCP server routes by KoolADE85 · Pull Request #3750 · plotly/dash

KoolADE85 · 2026-04-16T23:38:28Z

Summary

This PR pulls together everything from the previous PRs into a working MCP server you can connect to from any MCP-compatible LLM agent. Example:

claude mcp add dash-app --transport http http://localhost:8050/_mcp

Routes are added per MCP spec
Dash integration: control the feature with enable_mcp and mcp_path constructor params, (or DASH_MCP_ENABLED / DASH_MCP_PATH env vars)
E2E test suite: all the previous PRs have E2E coverage via the actual MCP server endpoints.
A number of one-liner type fixes since the mypy tests are now running in this PR.

github-actions · 2026-04-16T23:38:37Z

Thank you for your contribution to Dash! 🎉

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

chgiesse · 2026-04-20T07:31:19Z

Hi Plotly team!

First of all, thanks for integrating MCP into Dash - this looks really exciting!
But I would like to address/discuss some concerns:

this PR looks like its not compatible with the new bring your own Backend architecture by directly importing components like Response from Flask and not the response adapter - thus the mcp doesn't work with FastApi or Quart
the same seems to apply for the SSE streaming. Which I think should be integrated into the server adapter classes and be provided for the other backends too
and regarding the SSE implementation - I think the this version has some serious security implications - for synchronous Flask. With the current endless loop, session wise handling and Gunicorns default synchronous workers, the life time per session per sse stream blocks a complete worker! For example, google Chrome doesn't really provide a tab limit, so I could open a 1000 tabs and block a 1000 workers in your application. Although I think there is not a direct solutions to this (besides not providing endless stream capabilities to a synchronous backend) - a way to handle this would be to provide a DashQueueAdapter where a user can use a Gevent Queue instead of the default one. With this, the problem can be smoothed out in production. I also created a blog post ones - comparing server performance with SSE streams between Flask and Quart. https://community.plotly.com/t/flash-1-2-0-streaming-ui-updates-via-server-sent-events/93890/2

Let me know what you think - if you see it the same way or if I overlooked something! Would also love to contribute these changes :)

Best regards,
Christian

KoolADE85 · 2026-04-22T15:20:23Z

Hey @chgiesse

Thanks for the comments, and happy to see the excitement around the feature!

I'll be adjusting this to be compatible with the "bring your own backend" initiative. As you can see, the two projects have been happening independently so I'll make the appropriate code adjustments here.
As for SSE streaming, I'm thinking to remove that for the initial release. Early on, I thought it would be useful to have some server-driven messaging, and this would represent the start of that. But since the core functionality is all achieved with basic, well-described tools/resources, it's probably wise to remove SSE until we think through the security and performance considerations.

And absolutely, I'd welcome any contributions you have towards this effort - there's tons of potential to make Dash apps even more LLM friendly!

Adrian

chgiesse · 2026-05-05T09:48:55Z

Hi @KoolADE85

Thanks for the response and making it compatible! Looking forward to use it!

Yes I also think that the functionality without sse is already a good starting point. Maybe providing it together with a native sse callback? :)

…0 for missing session)

…n reload

camdecoster · 2026-05-12T15:25:20Z

            [
                {
-                    "id": str(comp.id),
+                    "id": str(getattr(comp, "id", None)),


Doesn't line 49 guarantee that id exists?

camdecoster · 2026-05-12T15:31:11Z

+    if pattern is None:
+        return None
+    matches = find_matching_components(pattern)


Suggested change

if pattern is None:

return None

matches = find_matching_components(pattern)

matches = find_matching_components(pattern) if pattern else None

camdecoster · 2026-05-12T15:36:26Z

-    dep: CallbackDependency, value: Any
-) -> CallbackInput | list[CallbackInput]:
+def _expand_dep(dep: CallbackDependency, value: Any) -> CallbackInputs:
    """Attach a concrete value to a callback dependency to produce a valid callback input.


Claude 😠!

Suggested change

"""Attach a concrete value to a callback dependency to produce a valid callback input.

"""

Attach a concrete value to a callback dependency to produce a valid callback input.

camdecoster · 2026-05-12T15:38:57Z

-                concrete_ids = [comp.id for comp in find_matching_components(pattern)]
-            expanded = [{"id": cid, "property": prop} for cid in concrete_ids]
+                concrete_ids = [
+                    getattr(comp, "id") for comp in find_matching_components(pattern)


Could comp be None here?

camdecoster · 2026-05-13T18:53:23Z

+    if func is not None:
+        return _wrap(func)
+    return _wrap


Do you need to return the wrapping function here?

camdecoster · 2026-05-13T19:14:35Z

+    app.mcp_decorated_functions = dict(MCP_DECORATED_FUNCTIONS)
+    MCP_DECORATED_FUNCTIONS.clear()
+
+    _session_id: str | None = None


Could you look into what would happen to this value if multiple users attempt to connect at the same time? Would some users end up with the wrong session id? It's a classic TOCTOU race condition 🙄.

Could multiple gunicorn works get there own session id? You mentioned this during our review.

KoolADE85 requested review from T4rk1n, camdecoster and ndrezn as code owners April 16, 2026 23:38

KoolADE85 added the no-issue-needed label Apr 16, 2026

KoolADE85 force-pushed the feature/mcp-server-integration branch from 876285b to 43c15b2 Compare April 17, 2026 00:32

camdecoster assigned KoolADE85 Apr 17, 2026

KoolADE85 force-pushed the feature/mcp-get-dash-component-tool branch from 8c1f392 to f9b05da Compare April 21, 2026 17:28

KoolADE85 force-pushed the feature/mcp-server-integration branch from 43c15b2 to f03c72f Compare April 21, 2026 17:50

KoolADE85 force-pushed the feature/mcp-get-dash-component-tool branch from f9b05da to bc340e6 Compare April 22, 2026 21:37

KoolADE85 force-pushed the feature/mcp-server-integration branch 2 times, most recently from d3e1e19 to 976e0df Compare April 23, 2026 15:29

KoolADE85 force-pushed the feature/mcp-get-dash-component-tool branch from bc340e6 to b3d4015 Compare April 23, 2026 20:24

KoolADE85 force-pushed the feature/mcp-server-integration branch from 20d3ee7 to bb25991 Compare April 23, 2026 20:49

KoolADE85 force-pushed the feature/mcp-get-dash-component-tool branch from b3d4015 to e407569 Compare April 30, 2026 15:24

KoolADE85 force-pushed the feature/mcp-server-integration branch from bb25991 to 9cc9959 Compare April 30, 2026 15:39

KoolADE85 force-pushed the feature/mcp-get-dash-component-tool branch from e407569 to 37e92f0 Compare April 30, 2026 16:02

KoolADE85 force-pushed the feature/mcp-server-integration branch from 9cc9959 to e84d208 Compare April 30, 2026 16:03

KoolADE85 force-pushed the feature/mcp-get-dash-component-tool branch from 37e92f0 to 28d5fed Compare April 30, 2026 16:45

KoolADE85 force-pushed the feature/mcp-server-integration branch from e84d208 to 943d9b2 Compare April 30, 2026 16:48

KoolADE85 force-pushed the feature/mcp-get-dash-component-tool branch from 28d5fed to f098f88 Compare May 6, 2026 21:35

KoolADE85 force-pushed the feature/mcp-server-integration branch from ac43cd0 to 8d7b8ba Compare May 6, 2026 21:37

KoolADE85 force-pushed the feature/mcp-get-dash-component-tool branch from f098f88 to 79df12e Compare May 8, 2026 15:40

KoolADE85 force-pushed the feature/mcp-server-integration branch 2 times, most recently from e0662fc to 3c39eac Compare May 8, 2026 21:56

KoolADE85 force-pushed the feature/mcp-get-dash-component-tool branch from f1b6cc2 to d25123b Compare May 8, 2026 22:04

KoolADE85 force-pushed the feature/mcp-server-integration branch from 3c39eac to a1ca057 Compare May 8, 2026 22:10

KoolADE85 changed the base branch from feature/mcp-get-dash-component-tool to mcp May 11, 2026 23:18

KoolADE85 force-pushed the feature/mcp-server-integration branch from a1ca057 to 409be55 Compare May 11, 2026 23:19

KoolADE85 added 13 commits May 12, 2026 17:25

Wire MCP server, SSE transport, and Dash app integration

4567a33

Enforce session management per MCP spec (404 for unknown sessions, 40…

7178c77

…0 for missing session)

remove unused code

78e0eec

Fix types for mypy

8199552

Remove unused SSE code for initial MCP implementation

bee8b21

add app-level config for exposing callback docstrings in MCP tools

b047e60

Disable MCP server by default

cf73ee3

lint

e943e97

fix leaky state in tests

fcc3546

Refactor unit tests to conform to existing test patterns

e2cd76d

Add decorator to make any function mcp-enabled

a2762e4

Notify connected agents of server restarts and hot-reloads so they ca…

2fc32c1

…n reload

Migrate MCP server to use v4.2.0 backend abstractions

b788678

KoolADE85 force-pushed the mcp branch from 3c340d1 to f5d408b Compare May 13, 2026 18:02

KoolADE85 force-pushed the feature/mcp-server-integration branch from 409be55 to b788678 Compare May 13, 2026 18:04

camdecoster reviewed May 13, 2026

View reviewed changes

Fix async (Quart) route registration

be418d7

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

MCP Server Part 8: MCP server routes#3750

MCP Server Part 8: MCP server routes#3750
KoolADE85 wants to merge 14 commits into
mcpfrom
feature/mcp-server-integration

KoolADE85 commented Apr 16, 2026 •

edited

Loading

Uh oh!

github-actions Bot commented Apr 16, 2026 •

edited

Loading

Uh oh!

chgiesse commented Apr 20, 2026

Uh oh!

KoolADE85 commented Apr 22, 2026

Uh oh!

chgiesse commented May 5, 2026 •

edited

Loading

Uh oh!

camdecoster May 12, 2026

Uh oh!

camdecoster May 12, 2026

Uh oh!

camdecoster May 12, 2026

Uh oh!

camdecoster May 12, 2026

Uh oh!

camdecoster May 13, 2026

Uh oh!

camdecoster May 13, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

	"""Attach a concrete value to a callback dependency to produce a valid callback input.
	"""
	Attach a concrete value to a callback dependency to produce a valid callback input.

Uh oh!

Conversation

KoolADE85 commented Apr 16, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Summary

Uh oh!

github-actions Bot commented Apr 16, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

chgiesse commented Apr 20, 2026

Uh oh!

KoolADE85 commented Apr 22, 2026

Uh oh!

chgiesse commented May 5, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

camdecoster May 12, 2026

Choose a reason for hiding this comment

Uh oh!

camdecoster May 12, 2026

Choose a reason for hiding this comment

Uh oh!

camdecoster May 12, 2026

Choose a reason for hiding this comment

Uh oh!

camdecoster May 12, 2026

Choose a reason for hiding this comment

Uh oh!

camdecoster May 13, 2026

Choose a reason for hiding this comment

Uh oh!

camdecoster May 13, 2026

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

KoolADE85 commented Apr 16, 2026 •

edited

Loading

github-actions Bot commented Apr 16, 2026 •

edited

Loading

chgiesse commented May 5, 2026 •

edited

Loading