System Prompt
Also called system message, developer message, system instruction.
A system prompt is a privileged instruction block, placed before the conversation, that sets a model's role, rules, tone, and constraints for every subsequent turn.
Description
Chat APIs typically expose the system prompt as a separate message role. Models trained with an instruction hierarchy are taught to give system instructions precedence over conflicting user or tool content, which makes the system prompt the main lever for operator control and a frequent target of prompt-leaking attacks.
Sources
- Ouyang et al. (2022). Training language models to follow instructions with human feedback.
- Wallace et al. (2024). The Instruction Hierarchy: Training LLMs to Prioritize Privileged Instructions.
Cite this entry
Protologue. (2026). System Prompt. In Protologue: A Taxonomy of Prompting and LLM Techniques (v1.0.0, PTL-0003). https://protologue.com/t/system-prompt/
BibTeX
@misc{protologue_system_prompt,
title = {System Prompt},
author = {{Protologue}},
year = {2026},
howpublished = {Protologue: A Taxonomy of Prompting and LLM Techniques, v1.0.0},
note = {Entry PTL-0003},
url = {https://protologue.com/t/system-prompt/}
}