Using SlormancerSaveParserService class :

const parsedSaveFile = this.slormancerSaveParserService.parseSaveFile(saveContent);

The parsed save file will be of type GameSave which contain the save raw data

Using SlormancerCharacterBuilderService class :

const character = this.slormancerCharacterBuilderService.getCharacterFromSave(parsedSaveFile, HeroClass.Mage);

The character result will be of type Character which is used by most build modifier classes