System Prompt

What it is

A system prompt is hidden instruction text that defines how an AI assistant should behave. It's set by developers before users interact with the AI and establishes the assistant's personality, capabilities, restrictions, and default behaviours. Users don't see the system prompt but experience its effects.

Why it matters

System prompts explain why different AI products built on the same underlying model behave differently. When building AI applications, your system prompt shapes the entire user experience. Understanding system prompts also helps you work with AI more effectively—you're interacting within constraints set by someone else.