Ruff Jupyter Extension Does Not work in Cursor

Support Bug Reports
1

Where does the bug appear (feature/product)?

Cursor IDE

Describe the Bug

Ruff Jupyter Extension does not work in Cursor. With the same configuration (settings.json), the formater does work in VS Code. I started noticing this like a week ago.

Version: 2.1.47
VSCode Version: 1.105.1
Commit: 2d3ce3499c15efd55b6b8538ea255eb7ba4266b0
Date: 2025-12-04T02:31:50.567Z
Electron: 37.7.0
Chromium: 138.0.7204.251
Node.js: 22.20.0
V8: 13.8.258.32-electron.0
OS: Darwin arm64 24.6.0

Steps to Reproduce

Try formatting on save notebook with the ruff extension.

Expected Behavior

It should autoformat on safe.

Operating System

MacOS

Current Cursor Version (Menu → About Cursor → Copy)

Version: 2.1.47
VSCode Version: 1.105.1
Commit: 2d3ce3499c15efd55b6b8538ea255eb7ba4266b0
Date: 2025-12-04T02:31:50.567Z
Electron: 37.7.0
Chromium: 138.0.7204.251
Node.js: 22.20.0
V8: 13.8.258.32-electron.0
OS: Darwin arm64 24.6.0
`

Does this stop you from using Cursor

Yes - Cursor is unusable

2

Hey, thanks for the report.

It seems like this could be exactly the incompatibility between Ruff Jupyter and Jupyter in Cursor (our docs mention that not all VS Code extensions work identically: Extensions | Cursor Docs).

To help us reproduce and pass this to the engineers, these details would be very helpful:

  1. Checks in Cursor:

    • Does Ruff work as a formatter in regular .py files (Format Document / formatting on save)?
    • If you press Format Document With... in a notebook cell - is Ruff in the list of formatters or does it not appear at all?

  2. Logs/screenshots:

    • Open the Output panel and check the Ruff and Jupyter channels during formatting attempts - are there errors? If yes, send the text.
    • Open Help → Toggle Developer Tools → Console and check for errors when saving the notebook.
    • Screenshots of notebook formatting settings in Cursor (Format on Save / Notebook-specific settings).

Once we have this data and a minimal repro, I’ll try to reproduce it myself and, if confirmed, raise it as a bug with the engineering team.

3

Thanks! Regarding your points:

  • Does Ruff work as a formatter in regular .py files (Format Document / formatting on save)? Yes, it works as expected

One key aspect is the following: In VS Code the code has the correct highlight and I can press fn + 12 to go to the function definition

image
image1324×1376 139 KB

(look nice orange and purple colors)

Whereas in Cursor I just get the white format (it is of course the same theme) and no function is clickable and I get no doctrings. Nothing. It is like is not properly recognized as Python code (also, not even type hints!):

image
image1172×1340 134 KB

Please, I am a heavy Jupyter User and this is blocking my workflow :confused:

6

ok! I just discovered this was a side effect of installing the Marimo VS Code extension. It works now :slight_smile: