Move the current pane left
panes
// what it does
Ctrl+b { runs swap-pane -U, exchanging the active pane with the previous pane in index order. The two panes trade places while your focus follows its original pane content. Use it to reposition a pane without breaking and rebuilding the split.
// shortcut
Ctrl + b{
// gotcha
It swaps by pane index (previous/next), not by on-screen direction, so { won't always move a pane visually leftward in an irregular or nested layout.