If we can only go with a single favicon (which rules out SVG thanks to Safari being backwards as usual), PNG support is essentially universal, so I recommend a 192 px PNG.

Updated to 192px PNG!

Sphinx says "It should be a Windows-style icon file (.ico), which is 16x16 or 32x32 pixels large" but it doesn't seem to matter.

Also "The image file will be copied to the _static directory of the output HTML, but only if the file does not already exist there", so let's put it there already. Keeps the root tidier too.

If we wanted to cover a lot of the possible options (to see them, go to https://realfavicongenerator.net/ and "Demo with a random image"), we could look at https://pypi.org/project/sphinx-favicon/

If we wanted to cover a lot of the possible options (to see them, go to https://realfavicongenerator.net/ and "Demo with a random image"), we could look at https://pypi.org/project/sphinx-favicon/

Yeah, I thought about that, I just figured it wasn't worth it for now just for the devguide