The orange bar on the left of a cell in JupyterLab indicates that the cell has been modified since it was last executed.

Quick Scoop

In recent JupyterLab versions (3.1+), a visual “dirty cell” indicator was added so you can quickly see which cells have changed after you last ran them. This appears as an orange-colored bar (the cell “collapser” area), often together with an orange execution counter and a small orange dot.

In other words: if you see the orange bar, JupyterLab is telling you: “This code isn’t the same as what you last ran.”

Once you re-run that cell successfully, the orange bar disappears because the edited state now matches the last execution.

Why this was added

  • Helps you track which cells you edited but forgot to run.
  • Useful in longer notebooks where you might scroll around and lose track of changes.
  • It is part of the broader “dirty cell indicator” feature introduced in the JupyterLab 3.1 changelog.

This is especially handy when debugging: if output looks wrong, you can check whether the cell feeding it still has that orange mark, meaning the current output might be stale.

Can you turn it off?

Yes, there are related experimental settings around document-wide undo/redo and notebook behavior. One common tweak people use is:

  1. Open Settings → Advanced Settings Editor in JupyterLab.
  1. Select Notebook on the left.
  1. Search for “undo” in the JSON editor and look for the experimental document-wide undo/redo setting.
  1. Toggle that option, then close and reopen JupyterLab.

Depending on your exact JupyterLab version, the precise setting name and effect can vary, but the orange bar itself is the “cell changed since last run” indicator.

Related visual cues (so you don’t mix them up)

  • In [*] to the left of a cell: means the cell is currently running or queued; when it finishes, the * becomes a number.
  • In [number]: the number is the order of execution in the current kernel session (1, 2, 3, …).

These are separate from the orange bar: the orange bar is about “edited after last run”, while the * or numbers are about execution status and order.

TL;DR

The orange bar on the left of a JupyterLab cell is a dirty cell indicator : it means the code in that cell has changed since the last time you executed it, and it clears once you run the cell again.

Information gathered from public forums or data available on the internet and portrayed here.