punchlines.ai is an AI joke generation tool built on top of a large language model (GPT-3.5 Turbo). It was fine-tuned on thousands of late night comedy monologue jokes (https://github.com/brendansudol/joke-gpt).
In terms of where it's incorporated in the code, the fine-tuned model id is stored in an environmental variable called `process.env.OPENAI_MODEL_ID` which then gets passed to the completion endpoint
web app is open-source, too: https://github.com/brendansudol/punchlines-ai