I cut Claude API costs by 90% with prompt caching. Here's what I learned before I had to shut it down.

867 Discord servers. 1,000+ active users. $10–11 every time someone played a one-hour D&D session. I was the only engineer. There was no revenue. And that number wasn't going down on its own. I want to be upfront before we go any further: Scrollbook is no longer running. I built it because I was always the Dungeon Master. My wife, my son, and I had a standing D&D night, and I wanted to actually play for once instead of running the whole session. So I built an AI dungeon master to take my seat. It worked well enough that I shared it. I did not expect anyone else to care. They did. 867 servers and 1,000+ users later, I was looking at $10-11 every time someone played a one-hour session with no revenue, no paywall, and no plan for either. (Scrollbook is one of three production projects I break down in my case studies . The other two are live and generating revenue. The contrast is instructive.) I shut it down because the cost of operating it solo, without a monetization model that kept pac