Hey! I would love to. I seriously considered adding my own key into the app, and implementing some rate limiting to e.g. allow you to send 3 messages for free. But unfortunately that would require me to store some backend data on you that I do not want: I want this to be a completely "private" / FE-only application that stores no data on anyone.
Testing YakGPT right now, excellent work! I would recommend adding some screenshots to the GitHub README so that people can get an idea of how it looks before entering their API key.
Before you comment something like this, ask yourself "How would I make this easier to try?" The only reasonable answer is providing the OP's own API key, which is undesirable.