System Prompt
1 min read · Reviewed 17 Oct 2026
In short
Standing instructions that apply to every message in a conversation.
In plain English
Separate from what you type each turn, a system prompt sets the rules up front: who the assistant is, how it should behave, what it must never do. Many tools let you set one in settings or custom instructions.
A real example
Putting your brand voice guide in a system prompt means you stop pasting it into every message — and the model applies it consistently instead of drifting back to its default after a few turns.
Why it matters
It is the highest-leverage prompting move most people never use. Anything you find yourself repeating belongs there.
