i3session remembers what's running in your i3 workspaces by saving a session file (in ~/.i3/session). It is then able to restore the running processes (and their simple orientation) to one or more workspaces.

Since i3session executes i3 commands sequentially (tree traversal), changing focus during restore will affect where clients open. By default, the i3-nagbar will appear during restore with a message to remind you of this.

Note: The restore command does not remove the current contents of a workspace, so you'll want to (manually) clear a workspace before restoring to it.

% i3session save
Saving...
Session saved to ~/.i3/session

% i3session restore 1
Restoring...
Session restored from ~/.i3/session

% i3session restore
Restoring...
Session restored from ~/.i3/session

• Python
• i3-py (https://github.com/ziberna/i3-py)
• i3-nagbar
• xprop
• PyXDG