WebSocket is not defined

[Arkhemis]

Hi,

I'm currently facing an issue with Jupyter in VSC. When I try to run a cell, I encounter the following error:

category: 'unknown',
isJupyterError: true,
originalException: [ReferenceError: WebSocket is not defined
at c:\Users~.vscode\extensions\ms-toolsai.jupyter-2025.2.0-win32-x64\dist\node_modules@jupyterlab\services\index.js:11:375
at c:\Users~.vscode\extensions\ms-toolsai.jupyter-2025.2.0-win32-x64\dist\node_modules@jupyterlab\services\index.js:1:35
at c:\Users~.vscode\extensions\ms-toolsai.jupyter-2025.2.0-win32-x64\dist\node_modules@jupyterlab\services\index.js:11:2662
at c:\Users~.vscode\extensions\ms-toolsai.jupyter-2025.2.0-win32-x64\dist\node_modules@jupyterlab\services\index.js:1:35
at c:\Users~.vscode\extensions\ms-toolsai.jupyter-2025.2.0-win32-x64\dist\node_modules@jupyterlab\services\index.js:17:18524
at c:\Users~.vscode\extensions\ms-toolsai.jupyter-2025.2.0-win32-x64\dist\node_modules@jupyterlab\services\index.js:1:35
at Object. (c:\Users~.vscode\extensions\ms-toolsai.jupyter-2025.2.0-win32-x64\dist\node_modules@jupyterlab\services\index.js:17:18706)
at Module._compile (node:internal/modules/cjs/loader:1484:14)
at Module._extensions..js (node:internal/modules/cjs/loader:1564:10)
at Module.load (node:internal/modules/cjs/loader:1295:32)
at Module.load (node:internal/modules/cjs/loader:1111:12)
at c.load (node:electron/js2c/node_init:2:16955)
at e.load (file:///c:/Users//AppData/Local/Programs/Microsoft%20VS%20Code/resources/app/out/vs/workbench/api/node/extensionHostProcess.js:190:10924)
at t._load (file:///c:/Users//AppData/Local/Programs/Microsoft%20VS%20Code/resources/app/out/vs/workbench/api/node/extensionHostProcess.js:182:22404)
at i.load (file:///c:/Users/~/AppData/Local/Programs/Microsoft%20VS%20Code/resources/app/out/vs/workbench/api/node/extensionHostProcess.js:174:21729)
at Module.require (node:internal/modules/cjs/loader:1318:19)
at require (node:internal/modules/helpers:179:18)
at Vpe (c:\Users~.vscode\extensions\ms-toolsai.jupyter-2025.2.0-win32-x64\dist\extension.node.js:301:18787)
at Z.start (c:\Users~.vscode\extensions\ms-toolsai.jupyter-2025.2.0-win32-x64\dist\extension.node.js:301:11486)
at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
at async eT.startKernel (c:\Users~.vscode\extensions\ms-toolsai.jupyter-2025.2.0-win32-x64\dist\extension.node.js:301:21741)
at async Wy.create (c:\Users~.vscode\extensions\ms-toolsai.jupyter-2025.2.0-win32-x64\dist\extension.node.js:301:24048)
at async y.createJupyterSession (c:\Users~.vscode\extensions\ms-toolsai.jupyter-2025.2.0-win32-x64\dist\extension.node.js:282:36917)
at async y.startJupyterSession (c:\Users~.vscode\extensions\ms-toolsai.jupyter-2025.2.0-win32-x64\dist\extension.node.js:282:34694)
at async y.start (c:\Users~.vscode\extensions\ms-toolsai.jupyter-2025.2.0-win32-x64\dist\extension.node.js:282:30778)
at async n.wrapKernelMethodImpl (c:\Users~.vscode\extensions\ms-toolsai.jupyter-2025.2.0-win32-x64\dist\extension.node.js:301:84148)]
}

I reinstalled VSC, reinstalled Python, deleted all requirements and reinstalled them and the issue persists. The strange thing is that jupyter is working outside VSC!

[benstager]

How does this have no answers? This is a massive issue that people have been facing

[thisiswhereitype]

There is also an issue here #16558

[mchlong]

same issue here

[sagar-roy-mulberri]

I downgraded from v2025.3.0 to v2025.2.0 and the issue went away

[Tomtunn]

here my jupyter log from v2025.3.0

17:14:50.014 [error] Error in notebook cell execution Error: Failed to start the Kernel 'base (Python 3.12.9)'. View Jupyter [log](command:jupyter.viewOutput) for further details. WebSocket is not defined > at new n (c:\Users\~\.vscode\extensions\ms-toolsai.jupyter-2025.3.2025032101-win32-x64\dist\extension.node.js:98:4480) > originalException = ReferenceError: WebSocket is not defined 17:14:50.014 [error] Error in execution (get message for cell) Error: Failed to start the Kernel 'base (Python 3.12.9)'. View Jupyter [log](command:jupyter.viewOutput) for further details. WebSocket is not defined > at new n (c:\Users\~\.vscode\extensions\ms-toolsai.jupyter-2025.3.2025032101-win32-x64\dist\extension.node.js:98:4480) > originalException = ReferenceError: WebSocket is not defined

[natalieintveld]

I have the same error, downgrade no use. My jupyter extension runtime status shows the uncaught error: 'WebSocket is not defined'.

[zhongjian-ls]

the same here. switched versions of jupyter extension/vscode, reinstall vscode, restart computer, nothing changed, still showing "no websocket"
env info:
macOS intel chip, vscode v1.99.3, jupyter ext v2025.3.0

[mchlong]

same issue for me

[sripadmini]

same issue here, downgraded and tried but no luck. Any updates on this?

[Gusnaud]

Same issue here just started happening today while I was busy working.

Im using Jupyter in WSL. I cant use windows unfortunately as many of the packages I need only support linux. So WSL is my only real option.

[DatasoftSolutionsNet]

Just started out of the blue for me also.... I changed nothing. One minute it was working fine, then the next I started getting the error.

I'm wondering if it's a server issue?

[nehaprabhu11]

My suspicion too. Are you using VS code using a remote connection? I am, and it's working just fine when I ssh to a different remote server, but not the one I need to work on right now. Very annoying!

[Gusnaud]

I am personally just "remoting" into my local WSL on my machine. The same error comes up on windows too, outside of WSL.

Im not sure if anything is remoting to anything outside of my local machine. I dont think so.

[jnelly79]

Its reassuring to see others are experiencing this error. @Gusnaud I am using wsl also and am experiencing the same problem. I am going to try and roll back my jupyter extenion first and if that doesn't work, then I will try rolling back my vscode version.

[Gusnaud]

I just tried this.
I went through all my packages and extensions, and I rolled back every version newer than 1 month where applicable.
No change, still get the same issue

[jnelly79]

@Gusnaud Nothing yet for me either.

[jnelly79]

@Gusnaud Okay, I don't know why this works, but after troubleshooting with Gemini for an hour, running this command within my wsl rm -rf ~/.vscode-server and starting vscode from within the directory.

[DatasoftSolutionsNet]

I just created a new workspace, and executed (ctrl-shift - P) Jupyter: Run in Dedicated Extension Host.
Now it seems to be working fine

[rayees05]

Thank you

[mohomayoun]

worked for me too after 5 hours of Chatgpt agent troubleshooting!

[zeedevio]

works!

[WilliamSMendes]

Thanks

[mlopez6132]

Thank you!

[janosspaits]

I have no idea why these things would interact, but uninstalling atlassian.atlascode extension from my devcontainer fixed the issue for me. The only difference between a working and not working dev container is choosing to not install atlassian.atlascode (horrendous extension for dev containers anyway).

[samarthinani1]

Can't thank you enough for sharing this.

[notuntoward]

This worked for me. Thanks.

[Linh-nk]

You just saved my day!!!

[RichardMairembam]

Thanks!! This also worked for me.

[quanguyen]

can't thank you enough. This trick works!

[bitadmiral]

Thanks for the fast resolution, @janosspaits. Simply reverting the Jira and Bitbucket (Atlassian Labs) extension from 3.6.0 back to the previous version (3.4.25) allowed my Jupyter notebooks to work again. Maybe wait for 3.6.1? 😛

Identifier: atlassian.atlascode
Version: 3.4.25
Last Updated: 2025-04-17, 10:56:10

[kelvinkrisna]

Super cool Atlassian Labs broke all Jupyters env hahah

[akashjn]

Uninstalled the Jira and Bitbucket (Atlassian Labs) extension v3.6.0 and switched back to the v3.4.25 and now the error is gone.

Installation
Identifier
atlassian.atlascode
Version
3.4.25
Last Updated
2025-04-17, 16:58:36
Size
6.65MB

[chaffeechenyefei]

Thank you and version 3.5.90 works too.

[HybridShivam]

Always the most random fixes!
Thanks

[zwei25]

Remove Jira and Bitbucket (Atlassian Labs) extension. We need to pay much attention to those extension in vs code. Two things we could prepare for the future problems:

• remove all the unnessary extensions in VS code
• uncheck the "Auto Update" for the extension we would like to keep.

[DonJayamanne]

Closing this discussion, as the problem had been identifed, and the problem would require a fix in the atlassian extension(s)

[Kugeleis]

@DonJayamanne Can it be somehow prevented that an extension not (visible to the user) involved in an action cripples vscode?

[DonJayamanne]

Unfortunately its not that simple.
In this case, its upto the user to figure out the faulty extension and report the issue to the extension.
As others have pointed out, you can run extension in separate ext host or just disable/uninstall the extensions causing these issues.