AI Glossary
What is System Prompt?
A special set of instructions given to an AI model before a conversation starts, used to define its behavior, role, tone, and constraints.
System Prompt explained
System prompts are the foundation of AI persona and skill design. Unlike regular user messages, system prompts are processed by the AI as background context that shapes every response in the conversation. In ChatGPT, this appears in "Custom Instructions". In Claude, it's the "System" field in the API. In most AI tools, it's the first thing the model reads before any user input. A good system prompt can transform a generic AI into a specialized expert.
Frequently asked questions
What is a system prompt?
A system prompt is a set of instructions provided to an AI model before the conversation begins. It defines the AI's role, personality, knowledge scope, and behavioral rules.
Where do I enter a system prompt?
In ChatGPT, use "Custom Instructions". In Claude, use the System field. In the API, it's the "system" parameter. In Cursor, it's the .cursorrules file or system prompt field.
How long should a system prompt be?
It depends on the complexity of the task. Simple personas may need 100-300 words. Complex skills with many rules and examples can be 1000+ words. Quality matters more than length.
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