prompt-engineering
System Instruction
System instructions (also called system prompt or meta-prompt) define the core behavioral constraints, goals, and persona of an AI model, set at the start of a session before any user input is processed.
System instructions are the primary mechanism for aligning a model with its operational goals. They define what the agent *is*, what it *does*, and what its *boundaries* are. In robust agent design, system instructions are often treated as immutable configuration rather than dynamic prompt input, and they are typically the first tokens cached in a prompt-caching pipeline.