What is System Prompt?

System Prompt is a high-priority instruction layer used to define how an AI assistant should behave, including role, constraints, and safety rules. System Prompt typically has higher precedence than user prompts.

Quick definition

System Prompt is the rule-setting instruction that guides an AI assistant’s behavior.

How System Prompt works

• System Prompt provides global instructions such as formatting and refusal rules.
• System Prompt can restrict which tools or actions are allowed.
• System Prompt influences how the model interprets user prompts.
• System Prompt can be targeted by prompt injection attempts.

Why System Prompt matters

System Prompt matters because System Prompt affects reliability, safety, and consistency.

System Prompt also affects measurement because changes to system behavior can change prompt performance.

Example use cases

• Defining that responses must be concise and include citations when available.
• Restricting the assistant from executing untrusted instructions from retrieved text.
• Standardizing output format for a prompt monitoring workflow.

Related terms

• User Prompt
• Prompt Engineering
• Prompt Injection
• Large Language Models (LLMs)
• Token Limit