AI Glossary
System prompt
system prompt, system instruction
A system prompt is a fixed instruction set before a conversation that defines the model's role, rules, and boundaries. It holds for the entire session, regardless of the user's subsequent questions.
- Sets the role, tone, and rules that hold for the whole conversation.
- Separates fixed rules from the user's variable instructions.
- It is part of guardrails, but on its own does not guarantee the model will honor them.
A system prompt addresses the need for an AI assistant to behave consistently no matter what the user types. It holds the fixed rules: the role, tone, scope of topics, and what is off-limits, and the model treats them with higher priority than any single question raised during the conversation.
In practice it separates the fixed rules from the variable instructions, which brings order to working with prompts and forms part of guardrails. On its own, though, a system prompt offers no hard guarantee: well-crafted user instructions can work around it, so critical constraints are worth enforcing outside the model as well.
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