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

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