System Prompt
LLM & Language ModelsHidden instructions given to an AI model by the application developer that define the AI's behavior, personality, knowledge boundaries, and rules — invisible to the end user.
A system prompt is the behind-the-scenes instruction set that shapes how an AI behaves in a specific application. When you use a customer service chatbot and it stays on-topic about that company's products, that's the system prompt at work.
System prompts typically define: the AI's role ('You are a helpful customer service agent for Acme Corp'), behavioral constraints ('Never discuss competitors,' 'Always be polite'), knowledge scope ('Only answer questions about our products'), response format ('Keep answers under 200 words'), and safety rules ('Never provide legal or medical advice').
Every AI-powered tool you use has a system prompt, even if you can't see it. ChatGPT has a default system prompt. Claude has one. Every custom GPT, every AI chatbot, every AI-powered feature has hidden instructions guiding the model's behavior.
Real-World Example
A system prompt sets the standing rules — the role, the constraints, the output shape — and applies to every turn, where a user prompt applies to one.
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What is System Prompt?
Hidden instructions given to an AI model by the application developer that define the AI's behavior, personality, knowledge boundaries, and rules — invisible to the end user.
How is System Prompt used in practice?
A system prompt sets the standing rules — the role, the constraints, the output shape — and applies to every turn, where a user prompt applies to one.
What concepts are related to System Prompt?
Key related concepts include Prompt, Prompt Engineering, Guardrails, Prompt Injection. Understanding these together gives a more complete picture of how System Prompt fits into the AI landscape.