It is a tool to convert the conversation history (json) of Hangouts to CSV.
I made it because there was no similar thing and I was in trouble. Please use all means.

(1) Download the Hangouts conversation history from https://takeout.google.com/settings/takeout in advance.
(2) Select [Hangouts.json] in the downloaded archive.
(3) If the preview is displayed without any problem, you can convert it to CSV.