What is a system prompt?

Understanding how ChatGPT works and how custom system prompts dictate an AI's behavior.

Written by Sohan Choudhury
January 15, 2025

Introduction to System Prompts

System prompts, also known as initial prompts, serve as the initial input to start a conversation with an AI like ChatGPT. They help set the context for the conversation, providing the AI with a "hint" about the type of response expected.

For example, ChatGPT's default system prompt is "You are ChatGPT, a large language model..." which helps set the context for its assistant-like behavior.

How does a system prompt work with ChatGPT?

When interacting with ChatGPT, the conversation starts with a system prompt. This prompt could be as simple as "You are ChatGPT, a helpful assistant." or more specific, like "You are an assistant that speaks like Shakespeare." In the latter case, the AI will generate responses in a Shakespearean style.

The AI, however, doesn't have any understanding of the context beyond what has been provided in the conversation. It doesn't have access to prior conversations unless those are included in the current conversation input.

Changing AI Use Case with Custom System Prompts

Custom system prompts provide an excellent way to adapt ChatGPT to a wide variety of specific applications. By tailoring the initial prompt, users can guide the AI's responses to fit particular scenarios.

Here are some examples of custom system prompts:

• Historical character: "You are Albert Einstein, explain the theory of relativity."
• Fictional character: "You are Harry Potter explaining Quidditch."
• Subject matter expert: "You are a professional biologist, explain the process of photosynthesis."

Remember, while the AI can mimic these roles, it doesn't truly understand them or have the real-life experiences or expertise of these characters or professionals.

Key Points to Remember

• System prompts guide the context of the AI's responses.
• The AI does not retain information between different conversations.
• Custom prompts can be used to adapt the AI to a wide variety of scenarios, but the AI doesn't truly understand or have the experiences or expertise of the roles it's asked to play.