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
ifpatternisNone:
returnNone
matches=find_matching_components(pattern)
matches=find_matching_components(pattern) ifpatternelseNone

This one was actually necessary for the linter too.

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
"""Attachaconcretevaluetoacallbackdependencytoproduceavalidcallbackinput.
"""
Attachaconcretevaluetoacallbackdependencytoproduceavalidcallbackinput.

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?

It cannot be None since find_matching_components only returns pattern-matching components (i.e. id is a dict), so getattr(comp, "id") is always a dict.

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?

This is because the decorator supports optional arguments:
func is None when used with arguments (@mcp_enabled(name="foo"))
It's not None when used bare (@mcp_enabled)

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.

This is now addressed in dadc63d

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 43c15b2Compare 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 f9b05daCompare April 21, 2026 17:28

KoolADE85 force-pushed the feature/mcp-server-integration branch from 43c15b2 to f03c72fCompare April 21, 2026 17:50

KoolADE85 force-pushed the feature/mcp-get-dash-component-tool branch from f9b05da to bc340e6Compare April 22, 2026 21:37

KoolADE85 force-pushed the feature/mcp-server-integration branch 2 times, most recently from d3e1e19 to 976e0dfCompare April 23, 2026 15:29

KoolADE85 force-pushed the feature/mcp-get-dash-component-tool branch from bc340e6 to b3d4015Compare April 23, 2026 20:24

KoolADE85 force-pushed the feature/mcp-server-integration branch from 20d3ee7 to bb25991Compare April 23, 2026 20:49

KoolADE85 force-pushed the feature/mcp-get-dash-component-tool branch from b3d4015 to e407569Compare April 30, 2026 15:24

KoolADE85 force-pushed the feature/mcp-server-integration branch from bb25991 to 9cc9959Compare April 30, 2026 15:39

KoolADE85 force-pushed the feature/mcp-get-dash-component-tool branch from e407569 to 37e92f0Compare April 30, 2026 16:02

KoolADE85 force-pushed the feature/mcp-server-integration branch from 9cc9959 to e84d208Compare April 30, 2026 16:03

KoolADE85 force-pushed the feature/mcp-get-dash-component-tool branch from 37e92f0 to 28d5fedCompare April 30, 2026 16:45

KoolADE85 force-pushed the feature/mcp-server-integration branch from e84d208 to 943d9b2Compare April 30, 2026 16:48

KoolADE85 force-pushed the feature/mcp-get-dash-component-tool branch from 28d5fed to f098f88Compare May 6, 2026 21:35

KoolADE85 force-pushed the feature/mcp-server-integration branch from ac43cd0 to 8d7b8baCompare May 6, 2026 21:37

KoolADE85 force-pushed the feature/mcp-get-dash-component-tool branch from f098f88 to 79df12eCompare May 8, 2026 15:40

KoolADE85 force-pushed the feature/mcp-server-integration branch 2 times, most recently from e0662fc to 3c39eacCompare May 8, 2026 21:56

KoolADE85 force-pushed the feature/mcp-get-dash-component-tool branch from f1b6cc2 to d25123bCompare May 8, 2026 22:04

KoolADE85 force-pushed the feature/mcp-server-integration branch from 3c39eac to a1ca057Compare May 8, 2026 22:10

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

KoolADE85 force-pushed the feature/mcp-server-integration branch from a1ca057 to 409be55Compare 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 f5d408bCompare May 13, 2026 18:02

KoolADE85 force-pushed the feature/mcp-server-integration branch from 409be55 to b788678Compare May 13, 2026 18:04

camdecoster reviewed May 13, 2026
View reviewed changes

KoolADE85 added 3 commits May 13, 2026 15:17

Fix async (Quart) route registration
be418d7

Fix session management with multiple workers
dadc63d

Fix CI errors after rebase
7f06fd7

KoolADE85 force-pushed the feature/mcp-server-integration branch from 5df8628 to 7f06fd7Compare May 14, 2026 15:06

code review feedback
ca9146e

KoolADE85 force-pushed the feature/mcp-server-integration branch from 750c20e to ca9146eCompare May 14, 2026 16:11

camdecoster approved these changes May 18, 2026
View reviewed changes

KoolADE85 merged commit 465a368 into mcpMay 19, 2026
29 checks passed

-ifpatternisNone:
-returnNone
-matches=find_matching_components(pattern)
+matches=find_matching_components(pattern) ifpatternelseNone

	"""Attachaconcretevaluetoacallbackdependencytoproduceavalidcallbackinput.
	"""
	Attachaconcretevaluetoacallbackdependencytoproduceavalidcallbackinput.

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chgiesse commented Apr 20, 2026

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KoolADE85 commented Apr 16, 2026•
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chgiesse commented May 5, 2026•
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