Thanks! The basic (default) version for the sentiment analysis is based on TextBlob library, but you can choose to activate deep learning to analyze sentiment with Google AI's BERT (trained on Twitter messages), though it is quite slow at the moment because inferences are made on a CPU and not a GPU.
The back-end is just Python/Flask and I use the free Algolia and Pushshift.io APIs to source the messages from HN and Reddit (big thanks to them!)