To add any Substack data sources to your app, just add the main base url as the source and set the data_type to substack.

from embedchain import App

app = App()

# source: for any substack just add the root URL
app.add('', data_type='substack')
app.query("Who is Brian Chesky?")
# Answer: Brian Chesky is the co-founder and CEO of Airbnb.