[Bug] Flask Debug Toolbar unexpectedly appears in GitHub Jupyter Notebook previews

[ycahning]

🏷️ Discussion Type

Bug

Body

Description

I noticed that a Flask Debug Toolbar is unexpectedly displayed as a dark, floating sidebar on the right side of Jupyter Notebook (.ipynb) previews on GitHub.

This behavior was not present when I viewed the same notebooks previously. It now occurs across multiple unrelated public repositories, including older notebooks that previously rendered normally.

Steps to reproduce

Open a public .ipynb file on GitHub, such as the Jupyter Notebook example.

Select the Preview tab if necessary.

Observe the right side of the rendered notebook.

Repeat in a Chrome Incognito window.

Expected behavior

The notebook should render normally without an unrelated developer debugging toolbar overlapping the content.

Actual behavior

A Flask Debug Toolbar appears on the right side of the notebook preview. It includes panels labeled Versions, Time, HTTP Headers, Request Vars, Config, Templates, SQLAlchemy, and Logging.

The issue persists in Chrome Incognito mode and can be reproduced across at least two unrelated public repositories.

Environment

Platform: GitHub.com

Browser: Google Chrome, including Incognito mode

Operating system: macOS

First observed: November 2, 2026

Affected file type: .ipynb

Additional information

Because this behavior appears across unrelated repositories, I suspect it may originate from a shared notebook rendering or preview component rather than the notebook files themselves.

I'm reporting this in case it represents an unintended exposure of developer debugging UI.

Screenshot

[vivianamarquez]

I'm seeing the same

[raulcarlomagno]

same here