A separate channel for rules
Chat models accept a system prompt that sits above the user turns. It is the place for durable behavior, the identity, tone, scope, and rules that should hold for every reply, not just the next one.
What belongs there
Good system prompts carry:
- Identity and role so the model knows what it is acting as.
- Standing rules such as what to refuse or always include.
- Tone and format defaults that shape every answer.
- Scope limits that say what is out of bounds.
What does not belong
Keep the specific task and the one off input in the user turn. The system prompt should stay stable so it can be cached and reused. Stuffing it with per request details makes it brittle and bloated.
Precedence
When a user request conflicts with a system rule, well aligned models favor the system prompt for safety and policy. This lets a developer set guardrails the end user cannot easily override mid chat.
Key idea
The system prompt is the stable top level channel for identity, rules, tone, and scope, kept free of per request detail so behavior holds across the whole conversation.