Phase 1 · Building with LLMs · Prompting
System prompts and roles
Set behavior once, separately from the conversation.
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Why it matters
Every LLM feature in a real product has a system prompt: the support bot, the copy assistant, the review tagger. It's where the developer sets behavior once, so each request only has to carry the task at hand. Getting that split right keeps prompts short, keeps thousands of replies consistent, and means a change to the brand voice is one edit instead of fifty.
What you'll be able to do
- Decide whether an instruction belongs in the system prompt or in a user message
- Write a system prompt that sets the audience, facts, rules and output style for an app
- Explain what the user and assistant roles hold, and the rules for ordering messages
- Reuse one system prompt across many requests in code
Before this lesson
Next in this phase: Examples in prompts