How to make a window transparent in Gnome?

I am not sure about Gnomw itself, but in Compiz, there is a plugin called "Opacity, Brightness and Saturation adjustments", which allows you control transparency of windows any way I can imagine, including Alt + {sroll} as Andrea Lazzarotto said.

For newer versions of Gnome (Gnome 3/Gnome Shell), you can use this extension to make windows transparent:

EDIT: To install in Gnome 3.14+

Gnome extensions have a file containing which version of Gnome they are compatible with - this is not always correct as the extension may work for other versions not specified in the file, so you need to get the extension from outside the gnome extension site, and modify the file and install it manually - this works a lot of the time with other extensions.

1. Go the the extension page, and download the extension zip file.

2. Extract it, and modify the shell-version line in the /transparentwindows-master/transparentwindows@ellen/metadata.json file to make sure it includes your shell version (e.g. 3.14):

    "shell-version": ["3.10", "3.12", "3.14"], 
   

   ^{You can find your shell version if needed using gnome-shell --version}

3. Move the extracted files to ~/.local/share/gnome-shell/extensions, so it looks like this:
4. The extension should now work, though you may need to restart the shell with Alt+F2+r+Enter, and enable it in Gnome Tweak Tool or similar.

Also note that you can do a issue/bug report to the developer to ask for the extension the Gnome Extension site to be updated - in this case there is one here. You can also make your own commit to the extension to include 3.14+ versions.

Gnome extensions are OK, but if someone want use opacity/transparency occasionally - it is better use xprop command.

Run:

xprop -format _NET_WM_WINDOW_OPACITY 32c -set _NET_WM_WINDOW_OPACITY 0x7FFFFFFF

and then click on window to set it to 50% opacity.

• 0x7FFFFFFF - 50% opacity
• 0xFFFFFFFF - 100% opacity

Set opacity via providing window id (obtained from xwininfo):

xprop -id 0x3a00006 -format _NET_WM_WINDOW_OPACITY 32c -set _NET_WM_WINDOW_OPACITY 0x7FFFFFFF