I had the same issue (at least it seemed the same), however it is possible to work around it if you are using the Python extension in conjunction with Remote Debugging.

You can ignore the extension's activation failure if that is your primary use, since VSCode is still able to debug remotely using Python Remote Attach.


After some more work on this, I found that updating the Python Extension to the pre-release version cleared up the various errors that came with the recent updates.

Answer from Zachary Barnett on Stack Overflow
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GitHub
github.com › microsoft › vscode-python › issues › 18109
Extension Activation failed · Issue #18109 · microsoft/vscode-python
December 3, 2021 - " Sorry, something went wrong activating IntelliCode support for Python. Please check the "Python" and "VS IntelliCode" output windows for details." And when I try running any python code, I get: "Couldn't start client Java Language Server" The python extension keeps loading as well. Open any python code in VSC.
Author   sherxyar
Discussions

VSCode-Python Extension Activation Failed
Type: Bug Environment Information Extension Version: 1.8.0 Python Extension Version: 2025.15.2025092201 Registered Environment Managers (3): - ms-python.python:system (Global) - ms-python.python:ve... More on github.com
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3
September 28, 2025
Visual studio code python extension error - Stack Overflow
Activating extension 'ms-python.python' failed: command 'python.viewOutput' already exists. workbench.desktop.main.js:2350 Cannot activate the 'Pylance' extension because its dependency 'Python' failed to activate · I tried to edit a python file with vscode and it shows extension activation failed More on stackoverflow.com
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visual studio code - How would I fix the issue of the python extension loading and Extension activation failed messages appearing? - Stack Overflow
Uninstall Python extension (if you have pylance uninstall it first). Uninstall any other extension that is failing. Close all instances of VS Code. Go to, %USERPROFILE%/.vscode/extensions (on windows) or ~/.vscode/extensions on Linux/Mac. More on stackoverflow.com
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Activating extension 'ms-python.python' failed: command 'python.setInterpreter' already exists.
Environment data Version: 1.41.1 Commit: 26076a4de974ead31f97692a0d32f90d735645c0 Date: 2019-12-18T14:57:51.166Z Electron: 6.1.5 Chrome: 76.0.3809.146 Node.js: 12.4.0 V8: 7.6.303.31-electron.0 OS: Darwin x64 19.2.0 VS Code version: 1.41.... More on github.com
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3
January 15, 2020
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Arch Linux Forums
bbs.archlinux.org › viewtopic.php
[SOLVED] VS Code, after upgrading: Python extension fails to load...? / Applications & Desktop Environments / Arch Linux Forums
UPDATE: I found https://github.com/microsoft/vscode-python/issues/15445 and now understand that I should use the CONSOLE-stuff from Help > Toggle Developer Tools. This reveals: *** Extension activation failed, run the 'Developer: Toggle Developer Tools' command for more information.
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GitHub
github.com › microsoft › vscode-python › issues › 25489
VSCode-Python Extension Activation Failed · Issue #25489 · microsoft/vscode-python
September 28, 2025 - SCode/resources/app/out/vs/workbench/api/node/extensionHostProcess.js:114:13345) at Vb.l (file:///c:/MyPrograms/Tools/VSCode/resources/app/out/vs/workbench/api/node/extensionHostProcess.js:114:12801) 2025-09-29 00:26:16.851 [info] Experiment 'pythonSurveyNotification' is active 2025-09-29 00:26:16.851 [error] extension activation failed Error: command 'python.viewOutput' already exists at ey.registerCommand (file:///c:/MyPrograms/Tools/VSCode/resources/app/out/vs/workbench/api/node/extensionHostProcess.js:114:40314) at Object.registerCommand (file:///c:/MyPrograms/Tools/VSCode/resources/app/ou
Author   duytrung
🌐
GitHub
github.com › microsoft › vscode-python › issues › 9578
Activating extension 'ms-python.python' failed: command 'python.setInterpreter' already exists. · Issue #9578 · microsoft/vscode-python
January 15, 2020 - Open a python file, python extension failed to load. Output for Python in the Output panel (View→Output, change the drop-down the upper-right of the Output panel to Python)
Author   shaozi
Find elsewhere
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GitHub
github.com › microsoft › vscode-python › issues › 24018
Python Extension Activation Failures and Inconsistent Behavior · Issue #24018 · microsoft/vscode-python
August 28, 2024 - Additionally, I have experienced similar issues with the Python extension for the past two years. However, during a period when I used GitHub Copilot for about five months, these issues did not occur. After discontinuing GitHub Copilot, the problems with the Python extension resumed.
Author   bzmarkovits
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GitHub
github.com › microsoft › vscode-python › issues › 24272
python extension activation failed · Issue #24272 · microsoft/vscode-python
October 8, 2024 - Python extension activation failed Message: run the Developer toggle developer tools command for more information Developer: Toggle Developer Tools command missing Version: 1.89.1 Commit: cf213cd39...
Author   CorneliuPopescu
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GitHub
github.com › microsoft › vscode-python › issues › 20456
Extension activation failed under latest insiders build · Issue #20456 · microsoft/vscode-python
January 4, 2023 - A few hours ago VSC was updated to the latest insiders build and upon restart the Python extension fails to load with the following error message being shown in the Developer Tools console: Activating extension 'ms-python.python' failed: this.a.sendEventData is not a function.
Author   ghylander
Top answer
1 of 3
19

I had this same issue and finally got it fixed!


If you are on an Linux and are using an Arch-based distro with AUR support, simply install the code-features package using:

yay -S code-features

or any AUR helper of your choosing.


On other operating systems, you should do the following:

Open your VSCode's product.json. I do not know where this file is on your operating system, so please do some research.

Look for the following line:

"extensionAllowedProposedApi": [ ...

Add the following entry to that array:

"ms-toolsai.jupyter": ["notebookConcatTextDocument", 
    "notebookControllerKind", "notebookDebugOptions", "notebookDeprecated", 
    "notebookEditor", "notebookEditorDecorationType", "notebookEditorEdit", 
    "notebookMessaging", "notebookMime", "notebookCellExecutionState", 
    "portsAttributes", "textDocumentNotebook", "quickPickSortByLabel"]

For example, if the line was originally:

"extensionAllowedProposedApi": [ "extension1", "extension2" ]

Then change it to:

"extensionAllowedProposedApi": [ "extension1", "extension2", 
    "ms-toolsai.jupyter": ["notebookConcatTextDocument", 
    "notebookControllerKind", "notebookDebugOptions", "notebookDeprecated", 
    "notebookEditor", "notebookEditorDecorationType", "notebookEditorEdit", 
    "notebookMessaging", "notebookMime", "notebookCellExecutionState", 
    "portsAttributes", "textDocumentNotebook", "quickPickSortByLabel"] ]

Note that with the second method, you will need to edit product.json every time you update VSCode.

2 of 3
6

Just ran into this today (I'm on MacOS for my work computer). In my case, upgrading to the pre-release version of the Jupyter extension (v2022.5.1001281006) solved it right away.

If you're not an experienced programmer/software engineer, as is the case for me, I suggest trying to upgrade (or roll back) either VS code or the plugin itself before going with your own dev code for the plugin, as with @CAG2 pt2 answer. (Personally, I had trouble finding a 'product.json' file; perhaps you need an insider's build of VS code for that kind of thing [edit]: https://code.visualstudio.com/api/advanced-topics/using-proposed-api, in which case I think you'd be editing 'package.json').

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GitHub
github.com › microsoft › vscode-python › issues › 24023
Extension activation failed when the notebook was opened and switched to restricted mode. · Issue #24023 · microsoft/vscode-python
August 29, 2024 - Extension activation failed when the notebook was opened and switched to restricted mode. Output for Python Language Server in the Output panel · 2024-08-29 09:42:33.180 [info] (Client) Pylance async client (2024.8.104) started with python extension (2024.13.2024082701) 2024-08-29 09:42:33.698 [info] [Info - 9:42:33 AM] (12876) Server root directory: file:///c:/Users/vting/.vscode-insiders/extensions/ms-python.vscode-pylance-2024.8.104/dist 2024-08-29 09:42:33.698 [info] [Info - 9:42:33 AM] (12876) Pylance language server 2024.8.104 (pyright version 1.1.378, commit ce64adc1) starting 2024-08-
Author   ttSpace
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Reddit
reddit.com › r/vscode › having an issue with the python extension
r/vscode on Reddit: Having an issue with the Python Extension
February 23, 2023 -

Hello, I am trying to download the Python extension from Microsoft and it's not working, I am getting this error:

Extension activation failed, run the 'Developer: Toggle Developer Tools' command for more information.

Additionally at the bottom, the spinning "Python extension loading..." just never finishes loading. I'm trying to debug my code and can't, can anyone help? Thank you !

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GitHub
github.com › microsoft › vscode-python › issues › 15972
Cannot activate the 'Python' extension because it depends on the 'Jupyter' extension, which is not loaded. Would you like to reload the window to load the extension? · Issue #15972 · microsoft/vscode-python
April 15, 2021 - Deleting the extension following file and reinstalling the extensions fix the issue for the current session: ~/vscode-server/extensions/ms-python.python-2021.3.680753044 ~/vscode-server/extensions/ms-toolsai.jupyter-2021.5.702919634
Author   20v100
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Reddit
reddit.com › r/vscode › stuck at vscode issue: "cannot activate the 'xxxx' extension because it depends on the 'python' extension, which is not loaded. "
r/vscode on Reddit: Stuck at VSCode issue: "Cannot activate the 'XXXX' extension because it depends on the 'Python' extension, which is not loaded. "
February 16, 2024 -

Does anyone else have this issue: I am running into a problem with VSCode complaining "Cannot activate the 'XXXX' extension because it depends on the 'Python' extension, which is not loaded. Would you like to reload the window to load the extension?"
The affected extensions appear to be:
- "ms-python.flake8"
- "charliermarsh.ruff"
- "eeyore.yapf"
As well as "ms-python.vscode-pylance" which also has the issue discussed in https://github.com/microsoft/pylance-release/issues/5019 - but the others have their issue even without pylance.
This is VS Code 1.86.1 with a remote devcontainer setup with the extensions installed via devcontainer.json.
After the Window Reload offered by the pop-up, the problem is resolved (until the next container restart).

A curious issue with Pylance is, that if it is not installed explicitly via devcontainer.json, it still gets pulled in but without a complaint.

Any ideas?

🌐
GitHub
github.com › microsoft › vscode-python › issues › 8632
Extension failed to activate due to error: Cannot read property 'length' of undefined · Issue #8632 · microsoft/vscode-python
November 17, 2019 - After installing the Python extension in VSCode, I'm getting the following error message. Error Python Extension: 2019-11-17 07:49:10: extension activation failed [TypeError: Cannot read property 'length' of undefined at m.update (c:\Users\[redacted]\.vscode\extensions\ms-python.python-2019.10.44104\out\client\extension.js:75
Author   wmeints
🌐
GitHub
github.com › microsoft › vscode-python › issues › 23131
Extension activation failed, run the 'Developer: Toggle Developer Tools' command for more information. · Issue #23131 · microsoft/vscode-python
March 26, 2024 - Extension activation failed, run the 'Developer: Toggle Developer Tools' command for more information.#23131 ... info-neededIssue requires more information from posterIssue requires more information from postertriage-neededNeeds assignment to ...
Author   datrine
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GitHub
github.com › microsoft › vscode-python › issues › 22995
Python extension loading issue · Issue #22995 · microsoft/vscode-python
February 28, 2024 - Type: Bug Extension activation failed, run the 'Developer: Toggle Developer Tools' command for more information. Extension version: 2024.3.10581547 VS Code version: Code 1.86.2 (903b1e9d899...
Author   krrishna2001
🌐
GitHub
github.com › microsoft › vscode-python › issues › 20354
Unable to load python extension · Issue #20354 · microsoft/vscode-python
December 9, 2022 - Type: Performance Issue Why do keep getting below error message ? Extension activation failed, run the 'Developer: Toggle Developer Tools' command for more information. Also 'Python ext...
Author   JanHof