A system prompt contains application-level instructions for the model, such as its role, allowed tools, safety boundaries, and response style. A user message contains the person's current request or data.
Model APIs usually give system or developer instructions higher priority than user content. That helps the application keep stable rules across many turns. However, a system prompt is not a security boundary. A determined user may still expose weaknesses, and the model cannot enforce database permissions or approval policies by itself.
Keep stable rules in the higher-priority message and request-specific details in the user message. Enforce hard constraints in code, then test conflicts such as a user asking the model to ignore its original instructions.
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