# Introduction: Understanding System Prompts

In the previous lesson, you learned how to make your prompts more effective by using clear instructions and positive reinforcement. Now, let's take a step further and talk about a special type of prompt called a **system prompt**.

A _system prompt_ is a message that sets the rules or context for how a language model should behave during a conversation. Unlike regular prompts, which are usually questions or requests from the user, `system prompts` act as instructions for the model itself. They help define the model's role, tone, or personality for the entire session.

For example, if you want the model to act like a helpful assistant, you can set a `system prompt` that tells it to do so. This is especially useful in chat platforms like _LibreChat_, where you might want the model to stay in character or follow specific guidelines throughout the conversation.

## Why Use System Prompts?

`System prompts` are necessary because they guide the model's behavior from the very beginning. They help you:

- Set the model's role (e.g., a teacher, a cat, an IT specialist)
- Control the tone and style of responses
- Limit or expand what the model can talk about

By using system prompts, you can ensure the model consistently follows your desired guidelines throughout the entire conversation.

## Example

Let's look at a real-world example. Imagine you are building a customer support chatbot. You want the chatbot to always be polite and only answer questions related to your product. By setting a `system prompt` like:

```text
You are a polite customer support agent. Only answer questions about our product.
```

The model will try to follow these instructions in every response.

`System prompts` are also helpful for creative tasks. For example, if you want the model to write stories as if it were a pirate, you can set a `system prompt` to make it talk like one.

## System Prompts in LibreChat

In the practices on our platform, you can set the system prompt in the following way.

Open the parameters section in the right sidebar:

Enter your system prompt in the "Custom Instructions" input field.

That's it! You don't have to click any "save" button; the system prompt is already here and will be applied to your next prompt.

## More Examples of System Prompts

Here are three different ways you can use system prompts to guide a language model's behavior:

1. **Limiting the Scope of Conversation**

```text
    Only answer questions related to healthy eating and nutrition. Politely decline to discuss any other topics.
    ```

2. **Enforcing a Specific Output Format**

```text
    When answering, always provide your response in a numbered list, with each point being one sentence long.
    ```

3. **Controlling the Level of Detail**

```text
    Give concise, one-sentence answers suitable for young children, avoiding technical jargon or complex explanations.
    ```

## Summary And What's Next

In this lesson, you learned what `system prompts` are and why they are essential. You saw how to write clear and effective `system prompts` and how to use them in _LibreChat_ to control the model's behavior.

Next, you'll get a chance to practice writing your own `system prompts` and see how they affect the model's responses. This hands-on practice will help you become more confident in guiding language models to behave precisely as you want.