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AI 101

System prompt

Sketch: a director hands an actor a role card (role, rules, tone); someone asks; the actor answers in role on stage.

A system prompt is a set of instructions the app gives the model before your message, setting its role, rules and tone.

Think of it like this: It is the rules card clipped to the dashboard before the trip starts: you steer, but the car already knows its limits.

Source:

https://platform.claude.com/docs/en/build-with-claude/prompt-engineering/system-prompts (checked Oct 15, 2026)

RelatedPrompt Harness Agent file (AGENTS.md)Context window

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