System Prompt

Also known as: System Message, System Instructions

In one sentence

Initial instructions given to an AI model that set its behaviour, personality, and constraints for an entire conversation.

Explain like I'm 12

Like telling a friend the rules before you start a game — it sets how the AI should act, what it should know, and what it shouldn't do, and those rules stay in place the whole time.

In context

A system prompt might say 'You are a helpful customer service agent for Acme Corp. Be polite, concise, and never share internal pricing. Always recommend contacting sales for custom quotes.' Every user message in that conversation follows these rules. Developers use system prompts to build focused AI products — a coding assistant, a legal advisor, or a children's tutor — all using the same underlying model but behaving very differently.

Related Guides

Learn more about System Prompt in these guides:

System Prompt Design: Building AI Products That Behave

Intermediate

Design production system prompts for AI-powered products. Covers instruction hierarchy, persona definition, output constraints, safety guardrails, and testing strategies.

13 min read

Prompt Injection Attacks and Defenses

Advanced

Adversaries manipulate AI behavior through prompt injection. Learn attack vectors, detection, and defense strategies.

8 min read

Context Engineering: Beyond Prompt Engineering