What Is the System Prompt?
Part of the Fundamentals section of Coddy's AI Prompts journey — lesson 17 of 23.
So far, every instruction you've given the AI has been through your messages—the user prompt. But there's another place where instructions live, and it runs quietly in the background: the system prompt.
Look at the chat panel. You'll see a field labeled "system prompt."
This is a special set of instructions that gets sent to the AI before your conversation even begins. It shapes how the AI behaves for the entire conversation.
Think of it this way: the user prompt is what you ask. The system prompt is who the AI is while answering.
A system prompt might say:
You are a helpful assistant that always responds in French.
Now, no matter what you ask, the AI will respond in French—without you having to request it each time. The system prompt sets the baseline behavior.
The system prompt is one of those hidden costs. It gets sent with every message, consuming input tokens even though you don't type it repeatedly.
Challenge
Use the system prompt field to change the AI's baseline behavior. Set a system prompt that makes the AI always end every response with the phrase “Have a great day!”
The AI's response must:
- End with
Have a great day!
Cheat sheet
The system prompt is a special set of instructions sent to the AI before the conversation begins. It shapes how the AI behaves for the entire conversation.
While the user prompt is what you ask, the system prompt defines who the AI is while answering.
Example system prompt:
You are a helpful assistant that always responds in French.
With this system prompt, the AI will respond in French to all messages without needing to request it each time.
The system prompt gets sent with every message, consuming input tokens even though you don't type it repeatedly.
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All lessons in Fundamentals
1Welcome to the AI Era
What Even Is AI?AI Is Not GoogleAI Is Not a HumanYour First Real TaskThe AI Can Be WrongWhat Is a "Model"?4The System Prompt
What Is the System Prompt?Setting Personality and RoleSetting Rules and ConstraintsSystem Prompt vs. User PromptSystem Prompt ConflictsCrafting a System PromptSystem Prompt Injection3Writing Your First Prompts
AI Talks Markdown (By Default)Controlling the Output FormatControlling Tone and StyleWhen the AI Ignores You