voice-agent-builder

Voice Agent Builder

Build, configure, and manage Voice AI agents. Supports Vapi (primary), Bland.ai, and Retell platforms.

Quick Start

export VAPI_API_KEY="your-vapi-api-key"

# Create a voice agent
python3 {baseDir}/scripts/vapi_agent.py create-agent '{"name":"Sales Agent","firstMessage":"Hi! How can I help you today?","systemPrompt":"You are a helpful sales assistant for Acme Corp."}'

# Make an outbound call
python3 {baseDir}/scripts/vapi_agent.py call '{"assistantId":"asst_xxx","phoneNumberId":"pn_xxx","customer":{"number":"+15551234567"}}'

# List agents
python3 {baseDir}/scripts/vapi_agent.py list-agents

# List calls
python3 {baseDir}/scripts/vapi_agent.py list-calls

Platform Comparison

Feature	Vapi	Bland.ai	Retell
Best For	Custom agents, dev-friendly	Simple outbound campaigns	Enterprise, low latency
Latency	~800ms	~500ms	~500ms
Languages	100+	30+	30+
Custom LLM	✅ Any OpenAI-compatible	✅ Limited	✅ Via API
Phone Numbers	Buy/import	Buy/import	Buy/import
Pricing	$0.05/min + provider costs	$0.09/min all-in	$0.07-0.15/min
WebSocket	✅	❌	✅
Knowledge Base	✅ Built-in	✅	✅
Transfers	✅	✅	✅

Recommendation: Start with Vapi — most flexible, best docs, largest community. Use Bland for simple high-volume outbound. Use Retell for enterprise low-latency needs.

See {baseDir}/scripts/voice_comparison.md for detailed breakdown.

Agent Creation Workflow

1. Choose a Voice

Vapi supports multiple TTS providers:

• ElevenLabs — Best quality, most natural (recommended)
• PlayHT — Good quality, lower cost
• Deepgram — Fast, good for real-time
• Azure — Enterprise, many languages

2. Configure the Agent

{
  "name": "Appointment Setter",
  "firstMessage": "Hi! This is Sarah from Dr. Smith's office. I'm calling to help you schedule your appointment.",
  "systemPrompt": "You are Sarah, a friendly appointment scheduler...",
  "voice": {
    "provider": "11labs",
    "voiceId": "21m00Tcm4TlvDq8ikWAM"
  },
  "model": {
    "provider": "openai",
    "model": "gpt-4o",
    "temperature": 0.7
  },
  "endCallFunctionEnabled": true,
  "maxDurationSeconds": 300,
  "silenceTimeoutSeconds": 30
}

3. Prompt Engineering for Voice

Voice prompts differ from text. Key principles:

• Keep responses SHORT — 1-2 sentences max per turn
• Be conversational — use filler words naturally ("Sure thing!", "Got it!")
• Handle interruptions — voice agents get cut off, design for it
• Confirm understanding — repeat back key info (names, numbers, dates)
• Include fallback — "I didn't catch that, could you repeat?"

4. Phone Number Setup

# List available phone numbers
python3 {baseDir}/scripts/vapi_agent.py list-phones

# Buy a number (via Vapi dashboard or API)
# Import existing number (Twilio, Vonage)
python3 {baseDir}/scripts/vapi_agent.py import-phone '{"provider":"twilio","number":"+15551234567","twilioAccountSid":"AC...","twilioAuthToken":"..."}'

5. Call Handling

Outbound calls:

python3 {baseDir}/scripts/vapi_agent.py call '{"assistantId":"asst_xxx","phoneNumberId":"pn_xxx","customer":{"number":"+15551234567"}}'

Inbound: Assign agent to phone number in Vapi dashboard, or via API:

python3 {baseDir}/scripts/vapi_agent.py update-phone '{"id":"pn_xxx","assistantId":"asst_xxx"}'

Integration Patterns

Voice + CRM (GHL)

1. Voice agent qualifies lead on call
2. Use Vapi's serverUrl webhook to capture call data
3. On call end → create/update GHL contact
4. Move opportunity to appropriate pipeline stage
5. Schedule follow-up if needed

Voice + Calendar Booking

1. Agent checks availability via calendar API
2. Uses function calling to book appointment
3. Confirms date/time verbally
4. Sends SMS confirmation after call

Voice + Knowledge Base

Upload documents to Vapi's knowledge base for RAG:

python3 {baseDir}/scripts/vapi_agent.py create-kb '{"name":"Product FAQ","files":["faq.pdf"]}'

Available Commands

python3 {baseDir}/scripts/vapi_agent.py create-agent '{...}'     # Create new agent
python3 {baseDir}/scripts/vapi_agent.py get-agent <id>            # Get agent details
python3 {baseDir}/scripts/vapi_agent.py list-agents               # List all agents
python3 {baseDir}/scripts/vapi_agent.py update-agent <id> '{...}' # Update agent
python3 {baseDir}/scripts/vapi_agent.py delete-agent <id>         # Delete agent
python3 {baseDir}/scripts/vapi_agent.py call '{...}'              # Make outbound call
python3 {baseDir}/scripts/vapi_agent.py get-call <id>             # Get call details
python3 {baseDir}/scripts/vapi_agent.py list-calls                # List all calls
python3 {baseDir}/scripts/vapi_agent.py list-phones               # List phone numbers
python3 {baseDir}/scripts/vapi_agent.py import-phone '{...}'      # Import phone number
python3 {baseDir}/scripts/vapi_agent.py update-phone '{...}'      # Update phone config

Credits

Built by M. Abidi | agxntsix.ai YouTube | GitHub Part of the AgxntSix Skill Suite for OpenClaw agents.

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