PromptSharp › Glossary › System Prompt
What is System Prompt?
A system prompt is a persistent instruction that sets the model's role, rules, and behavior for the whole conversation.
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.
Frequently asked
What is the difference between a system prompt and a user prompt?
The system prompt sets persistent behavior — role, rules, tone — for the whole conversation. The user prompt is each individual request. System instructions take priority and don't need repeating each turn.
Can I set a system prompt in ChatGPT?
In the ChatGPT app, 'Custom Instructions' act like a lightweight system prompt. Via the API, you set an explicit system message. Claude and Gemini expose similar system-level instructions.
Related terms
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