What the Roblox page says
The official experience description is the current source for this guide. It does not document controls, prompts, named NPCs, or build limits.
For NPC Builders Demo NPC builders, the creator says players can ask NPCs to create objects in the world. The description says the NPCs use a creator-made structured toolbox algorithm and mimic the use of F3X Builder tools. It also says the system is not generative AI.
Searches for F3X NPC Builders Demo lead to the same creator-stated relationship: the listing says the NPCs mimic F3X Builder tools, but it does not publish commands, limits, or implementation details.
This NPC Builders Demo mechanics summary is limited to that creator-published description; it is not a control guide or an undocumented systems list.