Default configuration in tags. How do I know?

[pturmel]

It isn't a table, but a model.

Parse a JSON Tag?

The closest you can get right now is to retrieve the tag configuration model from a tag provider (via context's .tagManager then .getTagConfigModelAsync(provider)). You can interrogate the model with .getApplicableProperties(propertyset) for a given configuration (turned into a PropertySet). Not particularly simple.