How to create a counter in Excel online (Excel 365)

Solution 1:

There are two possible ways for O365 on the web:

  • Create a web add-in where you can develop a custom UI (it can be a task pane) with a counter, see Build an Excel task pane add-in.
  • Use Office scripts, see https://docs.microsoft.com/en-us/office/dev/scripts/resources/vba-differences for more information.

I suppose web add-ins is the right choice for a custom UI (a task pane).