Thanks for the info.
I was browsing tagmanager folder in Geany source at the same time and now it doesn't seem like great idea to convert what I have to Tagmanager format, which is perhaps used by symbol browser and some Geany internals probably, and doesn't fit calltips usage

OTOH, pipe-separated format can show Description (which docs state that is "currently unused and should be left empty.") if simply pipe isn't entered before description text.

Now my problem is how to tell Geany to parse function name that has . (dot) in the name. For example I'm creating .tags file for Geany Lua plugin and in filetypes.lua file I added:

    whitespace_chars=\s\t!\"#$%&'()*+,-/:;<=>?@[\\]^`{|}~

(taken from "filetypes.common" without . (dot) in it). My idea was to tell Geany to treat . (dot) like word character.
Unfortunately this didn't work, and I guess there must be some way to do it.

BTW I noticed that Geany displays drop-down autocomplete list with max 30 entries, and does not reduce entries as I type, which is no good