Word of the Day

System Prompt

A system prompt is a persistent instruction that sets the model's role, rules, and behavior for the whole conversation.

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A system prompt is a special, higher-priority instruction that defines who the model is and how it should behave — its role, tone, boundaries, and output rules — before the user's message. In chat apps it's often hidden; in APIs it's an explicit 'system' role separate from 'user' turns.

The user prompt is the specific request; the system prompt is the standing context that applies to every request in that session. Putting durable rules ('always answer in British English,' 'never give legal advice') in the system prompt keeps them in force without repeating them each turn.

Related: role prompting · prompt injection · prompt engineering · context window

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