How to Build Structured LLM Prompts
Learn how to use the Prompt Builder to craft well-structured prompts for any LLM API call.
Tool Used
Prompt Builder
Understand the three sections
Open the tool and note the three sections — System sets the AI persona/behavior, User is the human turn, Assistant pre-fills the model's response start. Each maps directly to a message role in the Chat Completions API.
Write your System prompt
Describe the role, constraints, and output format you want. Keep it focused: a clear persona (e.g. 'You are a concise JSON API') produces more predictable outputs than a vague one.
Add your User message
Enter the actual instruction or question the user would send. This is the main driver of the response, so be specific about the task and any relevant context.
Optionally add an Assistant prefix
An Assistant prefix pre-fills the start of the model's reply, which is useful for forcing a specific format such as '{' to begin a JSON response or 'Sure, here is the' to steer tone.
Copy the output
Click Copy as Text for simple use in playgrounds, or Copy as JSON Array to get a ready-to-paste messages array for direct API calls.
All done!
You are ready to use Prompt Builder like a pro.