What is the difference between system, User, and Assistant roles in ChatGPT ?

When you use API for OpenAI ChatGPT, Claude, Perplexity or many different AI models you will stand before the decision to make, which role should I use for a prompt? System, User or Assistant?

The answer is pretty straightforward, here is a breakdown:

System Role

You can use the System role to set the context and provide general pieces of information on how the model should behave. You can put here the tone of voice, steps to follow, standard behaviour etc.

When to use it:
Usually, you use it at the beginning of the conversation to set further interaction principles. For example, if you need the model to respond as some specialist.

Example:
System: You are experienced SEO specialist. You use your extended knowledge and any content you create is SEO optimised. If you are missing some information you should ask additional questions.

User Role

This role represents you as a user, the human in the conversation. Here you give commands and ask questions, that the model should respond to.

When to use:
This is the default role you should use. Whenever you need to ask questions or make the model to generate something you should use this role.

Example:
User: For main keyword "Artificial Intelligence" generate 5 complementary keywords

Assistant Role

This role represents the model itself responding to any question or command sent by the User.

When to use:
You should use it when you need to give examples, of how the answers should look like.

Example:
Assistant: machine learning, neural networks, automation, deep learning ai ethics