How do I prevent Vim from automatically resizing a window when others open or close?

Explanation

Setting winfixwidth on a window tells Vim not to adjust its width when other windows are created, closed, or resized with <C-w>=. This is essential for keeping sidebar-style panels — like a file explorer or a terminal — at a stable width while the main editing area freely resizes around them.

How it works

• :set winfixwidth marks the current window's width as fixed
• Vim will not touch that window's width during layout adjustments (e.g., :vsplit, <C-w>=, or closing another vertical split)
• The complementary option winfixheight protects horizontal height instead
• :set nowinfixwidth or :setlocal nowinfixwidth removes the lock

Example

You have a narrow file browser open on the left (20 columns wide) and a main code window on the right. Without winfixwidth, opening a new vertical split redistributes width equally:

Before split:         After :vsplit (no winfixwidth):
+------+----------+   +------+------+------+
| tree |   code   |   | tree | code | code |
| 20c  |   80c    |   | 33c  | 33c  | 33c  |  ← tree grew!
+------+----------+   +------+------+------+

With winfixwidth set in the tree window:

After :vsplit (with winfixwidth on tree):
+------+------+------+
| tree | code | code |
|  20c |  40c |  40c |  ← tree stays fixed
+------+------+------+

Tips

• Set it in a FileType autocommand to apply automatically to file explorer buffers: autocmd FileType netrw setlocal winfixwidth
• Pair with :vertical resize 20 to first set the desired width before locking it
• winfixbuf (Vim 9.0+) additionally prevents the buffer in the window from being changed