Technique Updated 2026-04

System Prompt

Definition

The System Prompt is the invisible instruction that defines an LLM's behavior, role and constraints before any user interaction.

See also in the glossary

P
Prompt
A prompt is the instruction or question you give an AI to get a response. It's the interface between you and the model.
P
Prompt Engineering
Prompt engineering is the art of crafting precise instructions to get the best results from an AI model.
L
LLM (Large Language Model)
An LLM is an AI model trained on billions of texts, capable of understanding and generating human language.
A
AI Agent
An AI agent is an autonomous system that uses an LLM to plan, decide and execute real tasks without human intervention at each step.

Tools that use system prompt

C
ChatGPT
The world's most used conversational AI assistant
4.6/5
C
Claude
The AI that understands nuance, by Anthropic
4.7/5
G
Gemini
Google's AI assistant with 1M token context
4.5/5
O
OpenClaw
The open source AI agent that turns your LLMs into autonomous workers
4.5/5

Frequently Asked Questions

Is the System Prompt visible to users?
No, in principle. It's sent behind the scenes by the developer. But 'prompt injection' techniques can sometimes reveal it.
What makes a good System Prompt?
It defines tone, role, boundaries and response format. A customer support chatbot will have a very different system prompt from a coding assistant.