# Cell execution "flash"

**URL:** <https://talk.observablehq.com/t/cell-execution-flash/10919>\
**Category:** Feedback\
**Created:** [October 15, 2026, 11:51pm UTC](https://talk.observablehq.com/t/cell-execution-flash/10919 "2026-10-15T23:51:49Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![akrawitz](https://yyz2.discourse-cdn.com/flex030/user_avatar/talk.observablehq.com/akrawitz/32/4375_2.png) [@akrawitz](https://talk.observablehq.com/u/akrawitz)\
**Post date:** [October 15, 2026, 11:51pm UTC](https://talk.observablehq.com/t/cell-execution-flash/10919/1 "2026-10-15T23:51:49Z")

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In old Observable, cells always had the “sidebar flash” when re-executed (I think?).

In new Observable, it seems to depend on the editing mode (not sure about my terminology).

For example, consider the boss’ Game of Life notebook:

Old Observable: [Patterns in Conway’s Game of Life / Mike Bostock | Observable](https://old.observablehq.com/@mbostock/patterns-in-conways-game-of-life)  
The oscillators, which keep re-executing, get the flashing sidebar.

Same notebook in new Observable: [https://observablehq.com/@mbostock/patterns-in-conways-game-of-life](https://observablehq.com/@mbostock/patterns-in-conways-game-of-life)  
No flashing sidebars. Unless you activate “Tinker mode” and then the flashing is there.

Is this intended? When exactly is it there versus not there?

Maybe I’m just a creature of habit, but I find the flash a nice visual indicator of re-execution, which aids in understanding how the notebook functions, and can distinguish between a cell that is not running versus a cell that is running, but whose output isn’t changing. (But perhaps it is considered a distraction in a published notebook that isn’t about “how notebooks work”?)

Thanks,  
Adam