---

name: retellai-hello-world description: "Retell AI hello world \u2014 AI voice agent and phone call automation.\n
Use when working with Retell AI for voice agents, phone calls, or telephony.\nTrigger
\ with phrases like "retell hello world", "retellai-hello-world", "voice agent"
.\n" allowed-tools: Read, Write, Edit, Bash(npm:), Bash(curl:), Grep version: 1.9.0 license: MIT author: Jeremy Longshore jeremy@intentsolutions.io tags:

• saas
• retellai
• voice
• telephony
• ai-agents compatibility: Designed for Claude Code

---

Retell AI Hello World

Overview

Create your first Retell AI voice agent and make a test phone call.

Prerequisites

• Completed retellai-install-auth
• A phone number registered in Retell AI Dashboard (or use web call for testing)

Instructions

Step 1: Create an LLM Configuration

import Retell from 'retell-sdk';
const retell = new Retell({ apiKey: process.env.RETELL_API_KEY! });

// Create LLM configuration (what the agent says)
const llm = await retell.llm.create({
  model: 'gpt-4o',
  general_prompt: `You are a friendly receptionist for Acme Corp.
    - Greet callers warmly
    - Ask how you can help
    - Take messages if needed
    - Be concise and professional`,
});
console.log(`LLM created: ${llm.llm_id}`);

Step 2: Create a Voice Agent

const agent = await retell.agent.create({
  response_engine: {
    type: 'retell-llm',
    llm_id: llm.llm_id,
  },
  voice_id: '11labs-Adrian',  // Choose from available voices
  agent_name: 'Acme Receptionist',
});
console.log(`Agent created: ${agent.agent_id}`);

Step 3: Make a Test Phone Call

// Outbound call (requires a registered phone number)
const call = await retell.call.createPhoneCall({
  from_number: '+14155551234',  // Your Retell number
  to_number: '+14155555678',    // Destination
  override_agent_id: agent.agent_id,
});
console.log(`Call initiated: ${call.call_id}`);

Step 4: Or Test with Web Call

// Web call (no phone number needed — great for testing)
const webCall = await retell.call.createWebCall({
  agent_id: agent.agent_id,
});
console.log(`Web call URL: ${webCall.call_id}`);
// Use retell-client-js-sdk to connect from browser

Step 5: Check Call Status

const callDetail = await retell.call.retrieve(call.call_id);
console.log(`Status: ${callDetail.call_status}`);
console.log(`Duration: ${callDetail.end_timestamp - callDetail.start_timestamp}ms`);
if (callDetail.transcript) {
  console.log(`Transcript: ${callDetail.transcript}`);
}

Output

• LLM configuration with custom prompt
• Voice agent with selected voice
• Test call initiated (phone or web)
• Call status and transcript retrieved

Error Handling

Error	Cause	Solution
422 Invalid voice_id	Unknown voice	List available voices in Dashboard
400 No phone number	Number not registered	Register number in Dashboard first
Call not connecting	Destination unreachable	Try web call for testing

Examples

Validate a first agent with a web call before using a phone number

Create a development agent with a short greeting and no external tools, then exercise it through the web-call interface using synthetic inputs. Confirm the selected voice, expected greeting, disconnect behavior, and redacted transcript. Only after this evidence is reviewed should a team attach a test phone number; production routing remains separate until the agent has a versioned preview and a documented fallback path.

Resources

• Retell AI Documentation
• Create Phone Call

Next Steps

Configure agent behavior: retellai-core-workflow-a