All terms
Prompting
System Prompt
A high-level instruction, separate from the user's message, that sets the model's behavior.
Definition
A system prompt is a high-level instruction, separate from the user's message, that defines a model's persona, constraints, and overall behavior for a session. It is where developers encode tone, safety rules, output formatting, and available tools. The model treats it as privileged — users generally cannot see or override it — making it a primary way to customize behavior without fine-tuning.