Is there a list of supported variables for each site?

[Doksha]

I've looked everywhere and basically the only resource for what values work is answers to issues and some common sense names {chapter} {page} and {extension} are about all I could figure out on my own.
is there a list, preferably one that shows what values work for each site?

Maybe I am just overlooking something obvious but finding anything is way too hard.

If there is it should probably be linked somewhere within the string formatting doc

[mikf]

  -K, --list-keywords         Print a list of available keywords and example
                              values for the given URLs

So for example gallery-dl -K https://danbooru.donmai.us/posts?tags=bonocho