what is a system prompt?
A system prompt is a short note the AI reads before your message, setting its tone, format, and what to do first. You can write one, but it can't hand the model facts or abilities it doesn't have.
It’s set once, by whoever built the app you’re using — not by you, typing in the box. That’s the real distinction from a regular prompt: a system prompt is instructions layered in before your first word ever arrives, and it can’t teach the model a fact or a skill it doesn’t already have.