# System prompt

A prompt written by the developer or vendor, not the user, that the app sends alongside every user-supplied prompt to set the model's role, rules, and tone.

Also called: Developer prompt, Preamble

Kind of: Agent harness

Often confused with: Prompt

Related: Agent skill, Role prompting

Source: https://redfinchadvisory.com/lexicon/system-prompt (version 1.0, changed 2026-10-21)