System message
A special up-front instruction that sets the model’s role and rules for the whole conversation.
Think of it like
The job description you give a new hire on day one — it colors everything they do afterward.
Example
“You are a terse assistant that only answers in bullet points” as a system message shapes every reply that follows.
How it actually works
The system message sits above the back-and-forth and defines persona, constraints, and priorities. Models are trained to weight it heavily, so it’s your main steering wheel for tone and behavior. It’s not bulletproof, though — clever user input can sometimes override it.
For product teams
Your primary control surface for consistent behavior — but don’t treat it as a hard security boundary.
For engineers
A high-priority role message prepended to the conversation, weighted above user turns in training.
Related
- User message — Sits alongside the user message.
- Prompt injection — Can be undermined by prompt injection.
Read anything AI without the jargon
Look up any term in plain English, or save terms as you read with the free Chrome extension.
Open DecoderAdd to Chrome