Voice Agents are conversational AIs that can be called or embedded. Lumen wraps ElevenAgents so you can build one without writing code.
The four levers
- System prompt — defines who the agent is and what it should do. Most important.
- Voice — defines how the agent sounds. Pick one your callers will want to listen to.
- Knowledge base — what the agent knows. Paste in product docs, FAQs, or your bio.
- Temperature — how creative vs focused. Lower for support agents, higher for creative companions.
Writing a system prompt
The best system prompts have four parts:
- Identity — who you are. (“You are a calm receptionist for an indie design studio.”)
- Goal — what you're trying to accomplish. (“Help callers schedule consultations.”)
- Rules — what you must and must not do. (“Always offer to email a confirmation. Never quote prices.”)
- Style — how you talk. (“Use short, warm sentences. Never use jargon.”)
Greeting
The greeting is the first line the agent says when a conversation starts. Make it short, warm, and end with a clear question that prompts the user to speak. Bad: “Hello, I am the AI assistant. How may I help you today?” Good: “Hi, thanks for calling. What can I help you with?”
Knowledge base
Paste documents directly. The agent will retrieve from them when relevant. Don't dump everything — quality beats quantity. A focused 5-page brief outperforms a 200-page dump.
Temperature
0.2-0.4 for support and FAQ agents (stay on-script).
0.5-0.7 for sales and onboarding (be flexible but reliable).
0.8-1.0 for creative companions and storytellers (be inventive).
After you train
Lumen gives you three deployment options: call (phone number), embed (web widget), or API (your own app). Start with embed — it's the fastest to test and the cheapest to run.