Writing System Prompts That Work

What the system prompt is for

The system prompt sets persistent rules: who the assistant is, what it should and shouldn't do, and how to format answers. It applies to every turn, so it's where you encode policy.

A solid structure

You are {role} for {audience}.
Always: {non-negotiables, tone, format}.
Never: {hard limits}.
If unsure or out of scope, say so instead of guessing.

Tips

• Put the most important rules first and last.
• Be concrete ("answer in ≤3 sentences") rather than vague ("be concise").
• Don't stuff knowledge here — use retrieval for facts and keep the system prompt about behavior.