System Prompt
Initial instructions that define an LLM's behavior, personality, and constraints for a conversation.
Overview
A system prompt is a special instruction provided at the beginning of an LLM conversation that sets the model's behavior, role, constraints, and output format for the entire interaction. Unlike user messages, system prompts are typically hidden from the end user and persist across all turns of a conversation.
Key Details
Effective system prompts define the model's persona, specify response format and length, establish safety boundaries, provide domain context, and set the tone. They are a primary tool for customizing LLM behavior in applications without fine-tuning. Best practices include being specific and explicit, providing examples, defining what the model should and shouldn't do, and testing extensively. System prompt engineering is a key skill for building LLM-powered applications.
Related Concepts
system prompt • prompt engineering lexicon • prompt template