Fundamentals

System Prompt

A system prompt is a special message that appears before the user's input, setting instructions and context for how the model should behave. It's separate from user prompts and typically not visible in the conversation. System prompts are used to define the model's role ('You are an expert doctor'), establish constraints ('Never recommend illegal activities'), or provide context ('This conversation is about physics'). A well-designed system prompt can dramatically improve consistency and alignment. Most API providers give you explicit control over the system prompt.