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System prompt

How models work Last reviewed 2026-06-11

Definition Standing instructions given to an AI model before any user input, defining its role, rules, tone, and limits. Users of a product usually never see the system prompt steering their conversation.

In more depth

Product builders use system prompts to make a general-purpose model behave like a specific assistant—telling it, for example, to answer only from provided documents or to decline to give legal advice. System prompts shape output significantly but are not unbreakable; crafted user input can sometimes override them, a technique known as prompt injection. When evaluating an AI tool, it is reasonable to ask the vendor how its instructions constrain the model and what safeguards back them up.

Related terms

PromptPrompt engineeringContext window

About the editor: MHSB Solutions, Research desk. MHSB Solutions is not a law firm. This glossary is educational information, not legal advice.

Educational information, not legal advice. AI terminology and tools change quickly; definitions reflect usage as of the last-updated date. For what bar associations and courts actually require of lawyers using AI, see legalaicompliance.help and consult a licensed attorney in your jurisdiction.