Used a 10-page system prompt for a chatbot that just needed to say "store hours are 9-5"

Client wanted a chatbot for their bakery website. Simple use case: answer questions about opening hours, location, and the menu.

I went full enterprise mode. I wrote a 2,000-word system prompt. I included the full history of the bakery (founded 1987). I added detailed instructions for tone ("warm but professional, like a trusted neighborhood friend"). I specified exact response lengths. I added a whole section about what NOT to say. I included sample dialogues.

Every single user message — including "what time do you open?" — was preceded by this 2,000-word monolith.

After a month, the client sent me a screenshot of their OpenAI bill. 90% of their token spend was the system prompt. The actual conversations were like 50 tokens each.

I rewrote the system prompt. It is now 40 words.

The bot performs identically.