Hi Francois:

There isn't an easy way to add it to the description of the slot, but here's one way you can do it.

You can configure a new Window Action for "By Task" and add it to the Planning > Schedule or Project > Planning menu.

​To do this:

1. Activate developer mode

2. Go to Settings > Technical > Window Actions, search for Planning Schedule. There are 3 window actions configured by default - By Project, By Employee and By Role.

3. Duplicate any one of these window actions, give it a custom name (for example, Custom: Planning Schedule) and change the value in the context field to {'search_default_group_by_task': 1, 'planning_expand_task': 1}​

4. Add this window action to a menu item. For example, if you want to add it to Planning > Schedule, go to Settings > Technical > Menu Items and edit the Planning/Schedule menu and add a sub menu called By Task that invokes this window action.

5. Refresh the browser window and access the new window action by going to Planning > Schedule > By Task 

6. You will now see the Gantt chart with the planned activities grouped by Task.