System Prompt

Definition

Hidden instructions that set an AI assistant's behaviour, tone and rules before it sees the user's question.

A system prompt is the behind-the-scenes directive that configures how a model responds - its persona, formatting, safety rules and how it should treat and cite sources. In AI answer engines it governs whether and how citations are shown, how many sources are used and how cautiously claims are made, all of which shape a brand's chance of visible attribution. While you cannot edit an engine's system prompt, knowing it exists explains why the same underlying model behaves very differently across products like ChatGPT, Perplexity and Copilot.