Connect Retell Voice Agents to Custom Functions

Overview

• This workflow allows you to trigger custom logic in n8n directly from Retell's Voice Agent using Custom Functions.
• It captures a POST webhook from Retell every time a Voice Agent reaches a Custom Function node.
• You can plug in any logic—call an external API, book a meeting, update a CRM, or even return a dynamic response back to the agent.

Who is it for

For builders using Retell who want to extend Voice Agent functionality with real-time custom workflows or AI-generated responses.

Prerequisites

• Have a Retell AI Account
• A Retell agent with a Custom Function node in its conversation flow (see template below)
• Set your n8n webhook URL in the Custom Function configuration (see "How to use it" below)
• (Optional) Familiarity with Retell's Custom Function docs
• Start a conversation with the agent (text or voice)

Retell Agent Example

To get you started, we've prepared a Retell Agent ready to be imported, that includes the call to this template.

• Import the agent to your Retell workspace (top-right button on your agent's page)
• You will need to modify the function URL in order to call your own instance.
• This template is a simple hotel agent that calls the custom function to confirm a booking, passing basic formatted data.

How it works

• Retell sends a webhook to n8n whenever a Custom Function is triggered during a call (or test chat).
• The webhook includes:
  • Full call context (transcript, call ID, etc.)
  • Parameters defined in the Retell function node
• You can process this data and return a response string back to the Voice Agent in real-time.

How to use it

1. Copy the webhook URL (e.g. https://your-instance.app.n8n.cloud/webhook/hotel-retell-template)
2. Modify the Retell Custom Function webhook URL (see template description for screenshots)
   • Edit the function
     
   • Modify the URL
     
3. Modify the logic in the Set node or replace it with your own custom flow
4. Deploy and test: Retell will hit your n8n workflow during the conversation

Extension Ideas

• Call a third-party API to fetch data (e.g. hotel availability, CRM records)
• Use an LLM node to generate dynamic responses
• Trigger a parallel automation (Slack message, calendar invite, etc.)

👉 Reach out to us if you're interested in analyzing your Retell Agent conversations.