For SillyTavern and some other 3rd party software, they are using https://github.com/malfoyslastname/character-card-spec-v2, which has many similarities in character, but lacks support for game and module.
Highly recommend to use L-GOS Spec which has more flexibility for extension. But if you already have legacy assets in character-card-spec-v2, this project offers you the tool to convert between L-GOS and character-card-spec-v2.