AI

System prompt

The top-level instructions that set an LLM's role, rules, and behavior for the whole session.

The system prompt is the standing brief the model reads before every user message — it defines persona, tone, boundaries, and output format. Unlike a one-off user prompt, it persists across the entire conversation, so it's where you put things like 'You are a support agent for Acme; never discuss competitors; always answer in JSON.' Think of it as the employee handbook versus a single task assignment. When you're building an AI feature, this is usually the highest-leverage knob you control.