AI2026-05-17

System Prompt

Also known as: System Prompt / システムプロンプト / システム指示

An initial instruction sent to an LLM before user conversation begins, defining the model's role, tone, constraints, and output format — the primary control surface for application-level behavior.

Overview

A System Prompt is provided to the LLM API in a dedicated slot separate from user messages. It sets the model's persona ('You are a customer support agent'), response language and format, prohibited topics, and any injected company knowledge. It is the most impactful single element for controlling chatbot or AI-agent behavior.

Security considerations

System Prompt content is typically hidden from end users, but prompt-injection attacks can leak or override it. Avoid embedding secrets in the System Prompt; implement critical access controls at the application layer rather than relying on prompt-level restrictions.