Imported from jeremylongshore/tons-of-skills-marketplace (skills/.curated/retellai-webhooks-events/SKILL.md). Install upstream with npx skills add jeremylongshore/tons-of-skills-marketplace --skill retellai-webhooks-events. Copyright stays with the author (MIT).

Retell AI Webhooks Events

Overview

Handle Retell AI webhook events for call lifecycle, transcripts, and function execution.

Prerequisites

• HTTPS webhook endpoint
• Agent configured with webhook URL

Instructions

Step 1: Configure Webhook URL

// Set webhook URL in agent configuration
await retell.agent.update(agentId, {
  webhook_url: 'https://your-app.com/webhooks/retell',
});

Step 2: Webhook Endpoint

import express from 'express';

const app = express();
app.post('/webhooks/retell', express.json(), async (req, res) => {
  const { event, call } = req.body;

  switch (event) {
    case 'call_started':
      console.log(`Call started: ${call.call_id} from ${call.from_number}`);
      break;

    case 'call_ended':
      console.log(`Call ended: ${call.call_id}`);
      console.log(`  Duration: ${call.duration_ms}ms`);
      console.log(`  Status: ${call.call_status}`);
      if (call.transcript) {
        await saveTranscript(call.call_id, call.transcript);
      }
      break;

    case 'call_analyzed':
      console.log(`Analysis ready: ${call.call_id}`);
      console.log(`  Summary: ${call.call_analysis?.call_summary}`);
      break;

    default:
      console.log(`Unhandled event: ${event}`);
  }

  res.status(200).json({ received: true });
});

Step 3: Handle Function Calls During Conversation

// When agent triggers a function, Retell calls your URL
app.post('/functions/book-appointment', express.json(), async (req, res) => {
  const { patient_name, phone, date, time } = req.body.args;

  // Process the booking
  const booking = await bookAppointment(patient_name, phone, date, time);

  // Return response for agent to speak
  res.json({
    result: `Appointment booked for ${patient_name} on ${date} at ${time}. Confirmation number: ${booking.id}`,
  });
});

Output

• Webhook handling for call lifecycle events
• Transcript storage on call completion
• Function execution during live calls

Error Handling

Examples

Process a duplicate webhook delivery safely

Verify the webhook signature, derive a stable event identifier, and record the event before invoking any downstream side effect. When the same identifier is received again, acknowledge it without re-sending a notification, creating a booking, or storing another transcript copy. Send only redacted event metadata to observability systems, and alert on sustained signature failures or delivery latency rather than logging the raw call payload.

Resources

• Retell AI Documentation
• retell-sdk npm

Next Steps

Common errors: retellai-common-errors